Introduce `refStorage` extension

Hi,

this patch series introduces a new refStorage extension and related tooling. While there is only a single user-visible ref backend for now, this extension will eventually allow us to determine which backend shall be used for a repository. Furthermore, the series introduces tooling so that the ref storage format becomes more accessible.

The series is structured as follows:

- Patches 1 - 3: preliminary refactorings that prepare for the introduction of the ref storage format.

- Patches 4 - 6: wire up the ref format when setting up the repository and creating a new one.

- Patches 7 - 8: introduction of envvars to control the ref format globally.

- Patches 9 - 11: amend our tooling to know how to access and set the ref storage format.

- Patch 12: small patch for t9500 to make it handle ref storage extensions in the future.

I've been kind of torn regarding how to name this in the user-facing parts. Even though the extension is called "refStorage", I rather opted to use "ref format" in the user-facing parts, which is similar in nature to the "object format". Changing the extension to be called "refFormat" would cause issues for JGit though, so it's likely not an option to change it now.

Anyway, I'd appreciate your thoughts and proposals and am happy to rename the user-facing parts if we get to a preferable agreement.

This series depends on 18c9cb7524 (builtin/clone: create the refdb with the correct object format, 2023-12-12) because it relies on the more careful setup of the repository's refdb during clones.

Thanks!

Patrick

Patrick Steinhardt (12):
t: introduce DEFAULT_REPO_FORMAT prereq
worktree: skip reading HEAD when repairing worktrees
refs: refactor logic to look up storage backends
setup: start tracking ref storage format when
setup: set repository's formats on init
setup: introduce "extensions.refStorage" extension
setup: introduce GIT_DEFAULT_REF_FORMAT envvar
t: introduce GIT_TEST_DEFAULT_REF_FORMAT envvar builtin/rev-parse: introduce --show-ref-format flag builtin/init: introduce --ref-format= value flag builtin/clone: introduce --ref-format= value flag
t9500: write "extensions.refstorage" into config

 Documentation/config/extensions.txt           | 11 +++
 Documentation/git-clone.txt                   |  6 ++
 Documentation/git-init.txt                    |  7 ++
 Documentation/git-rev-parse.txt               |  3 +
 Documentation/git.txt                         |  5 ++
 Documentation/ref-storage-format.txt          |  1 +
 .../technical/repository-version.txt          |  5 ++
 builtin/clone.c                               | 17 ++++-
 builtin/init-db.c                             | 15 +++-
 builtin/rev-parse.c                           |  4 ++
 refs.c                                        | 34 ++++++---
 refs.h                                        |  4 ++
 refs/debug.c                                  |  1 -
 refs/files-backend.c                          |  1 -
 refs/packed-backend.c                         |  1 -
 refs/refs-internal.h                          |  1 -
 repository.c                                  |  1 +
 repository.h                                  |  6 ++
 setup.c                                       | 63 +++++++++++++++--
 setup.h                                       |  9 ++-
 t/README                                      |  3 +
 t/t0001-init.sh                               | 70 +++++++++++++++++++
 t/t1500-rev-parse.sh                          | 17 +++++
 t/t3200-branch.sh                             |  2 +-
 t/t5601-clone.sh                              | 17 +++++
 t/t9500-gitweb-standalone-no-errors.sh        |  5 ++
 t/test-lib-functions.sh                       |  5 ++
 t/test-lib.sh                                 | 15 +++-
 worktree.c                                    | 24 ++++---
 29 files changed, 318 insertions(+), 35 deletions(-)
 create mode 100644 Documentation/ref-storage-format.txt

2.43.GIT

A limited number of tests require repositories to have the default repository format or otherwise they would fail to run, e.g. because they fail to detect the correct hash function. While the hash function is the only extension right now that creates problems like this, we are about to add a second extensions for the ref format.

Introduce a new DEFAULT_REPO_FORMAT prereq that can easily be amended whenever we add new format extensions. Next to making any such changes easier on us, the prerequisite's name should also help to clarify the intent better.

---
 t/t3200-branch.sh | 2 +-
 t/test-lib.sh     | 4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

index 6a316f081e..de7d3014e4 100755
@@ -519,7 +519,7 @@ EOF
 
 mv .git/config .git/config-saved
 
-test_expect_success SHA1 'git branch -m q q2 without config should succeed' '
+test_expect_success DEFAULT_REPO_FORMAT 'git branch -m q q2 without config should succeed' '
 	git branch -m q q2 &&
 	git branch -m q2 q
 '

index 876b99562a..dc03f06b8e 100644
@@ -1936,6 +1936,10 @@ test_lazy_prereq SHA1 '
 	esac
 '
 
+test_lazy_prereq DEFAULT_REPO_FORMAT '
+	test_have_prereq SHA1
+'
+
 # Ensure that no test accidentally triggers a Git command
 # that runs the actual maintenance scheduler, affecting a user's
 # system permanently.

2.43.GIT

Nit: s/extensions/extension

[snip]

Yeah, this is of course a possibility with this new prereq. I don't really know what to do about it though, and think that it does serve a sensible purpose. So... dunno.

Patrick

When calling git init --separate-git-dir=<new-path> on a preexisting repository, then we move the Git directory of that repository to the new path specified by the user. If there are worktrees present in the Git repository, we need to repair the worktrees so that their gitlinks point to the new location of the repository.

This repair logic will load repositories via get_worktrees(), which will enumerate up and initialize all worktrees. Part of initialization is logic that we resolve their respective worktree HEADs, even though that information may not actually be needed in the end by all callers.

In the context of git-init(1) this is about to become a problem, because we do not have a repository that was set up via setup_git_directory() or friends. Consequentially, it is not yet fully initialized at the time of calling repair_worktrees(), and properly setting up all parts of the repository in init_db() before we repair worktrees is not an easy thing to do. While this is okay right now where we only have a single reference backend in Git, once we gain a second one we would be trying to look up the worktree HEADs before we have figured out the reference format, which does not work.

We do not require the worktree HEADs at all to repair worktrees. So let's fix issue this by skipping over the step that reads them.

---
 worktree.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

index a56a6c2a3d..9702ed0308 100644
@@ -51,7 +51,7 @@ static void add_head_info(struct worktree *wt)
 /**
  * get the main worktree
  */
-static struct worktree *get_main_worktree(void)
+static struct worktree *get_main_worktree(int skip_reading_head)
 {
 	struct worktree *worktree = NULL;
 	struct strbuf worktree_path = STRBUF_INIT;

@@ -70,11 +70,13 @@ static struct worktree *get_main_worktree(void)
 	 */
 	worktree->is_bare = (is_bare_repository_cfg == 1) ||
 		is_bare_repository();
-	add_head_info(worktree);
+	if (!skip_reading_head)
+		add_head_info(worktree);
 	return worktree;
 }
 
-static struct worktree *get_linked_worktree(const char *id)
+static struct worktree *get_linked_worktree(const char *id,
+					    int skip_reading_head)
 {
 	struct worktree *worktree = NULL;
 	struct strbuf path = STRBUF_INIT;

@@ -93,7 +95,8 @@ static struct worktree *get_linked_worktree(const char *id)
 	CALLOC_ARRAY(worktree, 1);
 	worktree->path = strbuf_detach(&worktree_path, NULL);
 	worktree->id = xstrdup(id);
-	add_head_info(worktree);
+	if (!skip_reading_head)
+		add_head_info(worktree);
 
 done:
 	strbuf_release(&path);

@@ -118,7 +121,7 @@ static void mark_current_worktree(struct worktree **worktrees)
 	free(git_dir);
 }
 
-struct worktree **get_worktrees(void)
+static struct worktree **get_worktrees_internal(int skip_reading_head)
 {
 	struct worktree **list = NULL;
 	struct strbuf path = STRBUF_INIT;

@@ -128,7 +131,7 @@ struct worktree **get_worktrees(void)
 
 	ALLOC_ARRAY(list, alloc);
 
-	list[counter++] = get_main_worktree();
+	list[counter++] = get_main_worktree(skip_reading_head);
 
 	strbuf_addf(&path, "%s/worktrees", get_git_common_dir());
 	dir = opendir(path.buf);

@@ -137,7 +140,7 @@ struct worktree **get_worktrees(void)
 		while ((d = readdir_skip_dot_and_dotdot(dir)) != NULL) {
 			struct worktree *linked = NULL;
 
-			if ((linked = get_linked_worktree(d->d_name))) {
+			if ((linked = get_linked_worktree(d->d_name, skip_reading_head))) {
 				ALLOC_GROW(list, counter + 1, alloc);
 				list[counter++] = linked;
 			}

@@ -151,6 +154,11 @@ struct worktree **get_worktrees(void)
 	return list;
 }
 
+struct worktree **get_worktrees(void)
+{
+	return get_worktrees_internal(0);
+}
+
 const char *get_worktree_git_dir(const struct worktree *wt)
 {
 	if (!wt)

@@ -591,7 +599,7 @@ static void repair_noop(int iserr UNUSED,
 
 void repair_worktrees(worktree_repair_fn fn, void *cb_data)
 {
-	struct worktree **worktrees = get_worktrees();
+	struct worktree **worktrees = get_worktrees_internal(1);
 	struct worktree **wt = worktrees + 1; /* +1 skips main worktree */
 
 	if (!fn)

2.43.GIT

Nit: s/then we/we

In order to look up ref storage backends, we're currently using a linked list of backends, where each backend is expected to set up its next pointer to the next ref storage backend. This is kind of a weird setup as backends need to be aware of other backends without much of a reason.

Refactor the code so that the array of backends is centrally defined in "refs.c", where each backend is now identified by an integer constant. Expose functions to translate from those integer constants to the name and vice versa, which will be required by subsequent patches.

---
 refs.c                | 34 +++++++++++++++++++++++++---------
 refs.h                |  3 +++
 refs/debug.c          |  1 -
 refs/files-backend.c  |  1 -
 refs/packed-backend.c |  1 -
 refs/refs-internal.h  |  1 -
 repository.h          |  3 +++
 7 files changed, 31 insertions(+), 13 deletions(-)

index 16bfa21df7..e87c85897d 100644
@@ -33,17 +33,33 @@
 /*
  * List of all available backends
  */
-static struct ref_storage_be *refs_backends = &refs_be_files;
+static const struct ref_storage_be *refs_backends[] = {
+	[REF_STORAGE_FORMAT_FILES] = &refs_be_files,
+};
 
-static struct ref_storage_be *find_ref_storage_backend(const char *name)
+static const struct ref_storage_be *find_ref_storage_backend(int ref_storage_format)
 {
-	struct ref_storage_be *be;
-	for (be = refs_backends; be; be = be->next)
-		if (!strcmp(be->name, name))
-			return be;
+	if (ref_storage_format && ref_storage_format < ARRAY_SIZE(refs_backends))
+		return refs_backends[ref_storage_format];
 	return NULL;
 }
 
+int ref_storage_format_by_name(const char *name)
+{
+	for (int i = 0; i < ARRAY_SIZE(refs_backends); i++)
+		if (refs_backends[i] && !strcmp(refs_backends[i]->name, name))
+			return i;
+	return REF_STORAGE_FORMAT_UNKNOWN;
+}
+
+const char *ref_storage_format_to_name(int ref_storage_format)
+{
+	const struct ref_storage_be *be = find_ref_storage_backend(ref_storage_format);
+	if (!be)
+		return "unknown";
+	return be->name;
+}
+
 /*
  * How to handle various characters in refnames:
  * 0: An acceptable character for refs

@@ -2029,12 +2045,12 @@ static struct ref_store *ref_store_init(struct repository *repo,
 					const char *gitdir,
 					unsigned int flags)
 {
-	const char *be_name = "files";
-	struct ref_storage_be *be = find_ref_storage_backend(be_name);
+	int format = REF_STORAGE_FORMAT_FILES;
+	const struct ref_storage_be *be = find_ref_storage_backend(format);
 	struct ref_store *refs;
 
 	if (!be)
-		BUG("reference backend %s is unknown", be_name);
+		BUG("reference backend %s is unknown", ref_storage_format_to_name(format));
 
 	refs = be->init(repo, gitdir, flags);
 	return refs;

index 23211a5ea1..c6571bcf6c 100644
@@ -11,6 +11,9 @@ struct string_list;
 struct string_list_item;
 struct worktree;
 
+int ref_storage_format_by_name(const char *name);
+const char *ref_storage_format_to_name(int ref_storage_format);
+
 /*
  * Resolve a reference, recursively following symbolic refererences.
  *

index 83b7a0ba65..b9775f2c37 100644
@@ -426,7 +426,6 @@ static int debug_reflog_expire(struct ref_store *ref_store, const char *refname,
 }
 
 struct ref_storage_be refs_be_debug = {
-	.next = NULL,
 	.name = "debug",
 	.init = NULL,
 	.init_db = debug_init_db,

index ad8b1d143f..43fd0ac760 100644
@@ -3241,7 +3241,6 @@ static int files_init_db(struct ref_store *ref_store, struct strbuf *err UNUSED)
 }
 
 struct ref_storage_be refs_be_files = {
-	.next = NULL,
 	.name = "files",
 	.init = files_ref_store_create,
 	.init_db = files_init_db,

index b9fa097a29..8d1090e284 100644
@@ -1705,7 +1705,6 @@ static struct ref_iterator *packed_reflog_iterator_begin(struct ref_store *ref_s
 }
 
 struct ref_storage_be refs_be_packed = {
-	.next = NULL,
 	.name = "packed",
 	.init = packed_ref_store_create,
 	.init_db = packed_init_db,

index 4af83bf9a5..8e9f04cc67 100644
@@ -663,7 +663,6 @@ typedef int read_symbolic_ref_fn(struct ref_store *ref_store, const char *refnam
 				 struct strbuf *referent);
 
 struct ref_storage_be {
-	struct ref_storage_be *next;
 	const char *name;
 	ref_store_init_fn *init;
 	ref_init_db_fn *init_db;

index 5f18486f64..ea4c488b81 100644
@@ -24,6 +24,9 @@ enum fetch_negotiation_setting {
 	FETCH_NEGOTIATION_NOOP,
 };
 
+#define REF_STORAGE_FORMAT_UNKNOWN 0
+#define REF_STORAGE_FORMAT_FILES   1
+
 struct repo_settings {
 	int initialized;
 

2.43.GIT

The only purpose of this function will be to print error messages, so "unknown" seems like the better choice.

Good point, will change.

Patrick

In order to discern which ref storage format a repository is supposed to use we need to start setting up and/or discovering the format. This needs to happen in two separate code paths.

- The first path is when we create a repository via init_db(). When we are re-initializing a preexisting repository we need to retain the previously used ref storage format -- if the user asked for a different format then this indicates an erorr and we error out. Otherwise we either initialize the repository with the format asked for by the user or the default format, which currently is the "files" backend.

- The second path is when discovering repositories, where we need to read the config of that repository. There is not yet any way to configure something other than the "files" backend, so we can just blindly set the ref storage format to this backend.

Wire up this logic so that we have the ref storage format always readily available when needed. As there is only a single backend and because it is not configurable we cannot yet verify that this tracking works as expected via tests, but tests will be added in subsequent commits. To countermand this ommission now though, raise a BUG() in case the ref storage format is not set up properly in ref_store_init().

---
 builtin/clone.c   |  5 +++--
 builtin/init-db.c |  4 +++-
 refs.c            |  6 +++---
 refs.h            |  1 +
 repository.c      |  1 +
 repository.h      |  3 +++
 setup.c           | 26 +++++++++++++++++++++++---
 setup.h           |  6 +++++-
 8 files changed, 42 insertions(+), 10 deletions(-)

index 339af10c10..6840064b59 100644
@@ -1105,7 +1105,8 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	 * repository, and reference backends may persist that information into
 	 * their on-disk data structures.
 	 */
-	init_db(git_dir, real_git_dir, option_template, GIT_HASH_UNKNOWN, NULL,
+	init_db(git_dir, real_git_dir, option_template, GIT_HASH_UNKNOWN,
+		REF_STORAGE_FORMAT_UNKNOWN, NULL,
 		do_not_override_repo_unix_permissions, INIT_DB_QUIET | INIT_DB_SKIP_REFDB);
 
 	if (real_git_dir) {

@@ -1290,7 +1291,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	hash_algo = hash_algo_by_ptr(transport_get_hash_algo(transport));
 	initialize_repository_version(hash_algo, 1);
 	repo_set_hash_algo(the_repository, hash_algo);
-	create_reference_database(NULL, 1);
+	create_reference_database(the_repository->ref_storage_format, NULL, 1);
 
 	/*
 	 * Before fetching from the remote, download and install bundle

index cb727c826f..b6e80feab6 100644
@@ -11,6 +11,7 @@
 #include "object-file.h"
 #include "parse-options.h"
 #include "path.h"
+#include "refs.h"
 #include "setup.h"
 #include "strbuf.h"
 

@@ -236,5 +237,6 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 
 	flags |= INIT_DB_EXIST_OK;
 	return init_db(git_dir, real_git_dir, template_dir, hash_algo,
-		       initial_branch, init_shared_repository, flags);
+		       REF_STORAGE_FORMAT_UNKNOWN, initial_branch,
+		       init_shared_repository, flags);
 }

index e87c85897d..d289a5e175 100644
@@ -2045,12 +2045,12 @@ static struct ref_store *ref_store_init(struct repository *repo,
 					const char *gitdir,
 					unsigned int flags)
 {
-	int format = REF_STORAGE_FORMAT_FILES;
-	const struct ref_storage_be *be = find_ref_storage_backend(format);
+	const struct ref_storage_be *be;
 	struct ref_store *refs;
 
+	be = find_ref_storage_backend(repo->ref_storage_format);
 	if (!be)
-		BUG("reference backend %s is unknown", ref_storage_format_to_name(format));
+		BUG("reference backend is unknown");
 
 	refs = be->init(repo, gitdir, flags);
 	return refs;

index c6571bcf6c..944a67ac1b 100644
@@ -11,6 +11,7 @@ struct string_list;
 struct string_list_item;
 struct worktree;
 
+int default_ref_storage_format(void);
 int ref_storage_format_by_name(const char *name);
 const char *ref_storage_format_to_name(int ref_storage_format);
 

index a7679ceeaa..a75c1598b0 100644
@@ -184,6 +184,7 @@ int repo_init(struct repository *repo,
 		goto error;
 
 	repo_set_hash_algo(repo, format.hash_algo);
+	repo->ref_storage_format = format.ref_storage_format;
 	repo->repository_format_worktree_config = format.worktree_config;
 
 	/* take ownership of format.partial_clone */

index ea4c488b81..22c30cdbc9 100644
@@ -163,6 +163,9 @@ struct repository {
 	/* Repository's current hash algorithm, as serialized on disk. */
 	const struct git_hash_algo *hash_algo;
 
+	/* Repository's reference storage format, as serialized on disk. */
+	int ref_storage_format;
+
 	/* A unique-id for tracing purposes. */
 	int trace2_repo_id;
 

index 155fe13f70..c1bf106379 100644
@@ -1564,6 +1564,8 @@ const char *setup_git_directory_gently(int *nongit_ok)
 		}
 		if (startup_info->have_repository) {
 			repo_set_hash_algo(the_repository, repo_fmt.hash_algo);
+			the_repository->ref_storage_format =
+				repo_fmt.ref_storage_format;
 			the_repository->repository_format_worktree_config =
 				repo_fmt.worktree_config;
 			/* take ownership of repo_fmt.partial_clone */

@@ -1657,6 +1659,8 @@ void check_repository_format(struct repository_format *fmt)
 	check_repository_format_gently(get_git_dir(), fmt, NULL);
 	startup_info->have_repository = 1;
 	repo_set_hash_algo(the_repository, fmt->hash_algo);
+	the_repository->ref_storage_format =
+		fmt->ref_storage_format;
 	the_repository->repository_format_worktree_config =
 		fmt->worktree_config;
 	the_repository->repository_format_partial_clone =

@@ -1897,7 +1901,8 @@ static int is_reinit(void)
 	return ret;
 }
 
-void create_reference_database(const char *initial_branch, int quiet)
+void create_reference_database(int ref_storage_format,
+			       const char *initial_branch, int quiet)
 {
 	struct strbuf err = STRBUF_INIT;
 	int reinit = is_reinit();

@@ -1917,6 +1922,7 @@ void create_reference_database(const char *initial_branch, int quiet)
 	safe_create_dir(git_path("refs"), 1);
 	adjust_shared_perm(git_path("refs"));
 
+	the_repository->ref_storage_format = ref_storage_format;
 	if (refs_init_db(&err))
 		die("failed to set up refs db: %s", err.buf);
 

@@ -2135,8 +2141,20 @@ static void validate_hash_algorithm(struct repository_format *repo_fmt, int hash
 	}
 }
 
+static void validate_ref_storage_format(struct repository_format *repo_fmt, int format)
+{
+	if (repo_fmt->version >= 0 &&
+	    format != REF_STORAGE_FORMAT_UNKNOWN &&
+	    format != repo_fmt->ref_storage_format) {
+		die(_("attempt to reinitialize repository with different reference storage format"));
+	} else if (format != REF_STORAGE_FORMAT_UNKNOWN) {
+		repo_fmt->ref_storage_format = format;
+	}
+}
+
 int init_db(const char *git_dir, const char *real_git_dir,
-	    const char *template_dir, int hash, const char *initial_branch,
+	    const char *template_dir, int hash,
+	    int ref_storage_format, const char *initial_branch,
 	    int init_shared_repository, unsigned int flags)
 {
 	int reinit;

@@ -2179,13 +2197,15 @@ int init_db(const char *git_dir, const char *real_git_dir,
 	check_repository_format(&repo_fmt);
 
 	validate_hash_algorithm(&repo_fmt, hash);
+	validate_ref_storage_format(&repo_fmt, ref_storage_format);
 
 	reinit = create_default_files(template_dir, original_git_dir,
 				      &repo_fmt, prev_bare_repository,
 				      init_shared_repository);
 
 	if (!(flags & INIT_DB_SKIP_REFDB))
-		create_reference_database(initial_branch, flags & INIT_DB_QUIET);
+		create_reference_database(repo_fmt.ref_storage_format,
+					  initial_branch, flags & INIT_DB_QUIET);
 	create_object_directory();
 
 	if (get_shared_repository()) {

index 3f0f17c351..4927abf2cf 100644
@@ -115,6 +115,7 @@ struct repository_format {
 	int worktree_config;
 	int is_bare;
 	int hash_algo;
+	int ref_storage_format;
 	int sparse_index;
 	char *work_tree;
 	struct string_list unknown_extensions;

@@ -131,6 +132,7 @@ struct repository_format {
 	.version = -1, \
 	.is_bare = -1, \
 	.hash_algo = GIT_HASH_SHA1, \
+	.ref_storage_format = REF_STORAGE_FORMAT_FILES, \
 	.unknown_extensions = STRING_LIST_INIT_DUP, \
 	.v1_only_extensions = STRING_LIST_INIT_DUP, \
 }

@@ -175,10 +177,12 @@ void check_repository_format(struct repository_format *fmt);
 
 int init_db(const char *git_dir, const char *real_git_dir,
 	    const char *template_dir, int hash_algo,
+	    int ref_storage_format,
 	    const char *initial_branch, int init_shared_repository,
 	    unsigned int flags);
 void initialize_repository_version(int hash_algo, int reinit);
-void create_reference_database(const char *initial_branch, int quiet);
+void create_reference_database(int ref_storage_format,
+			       const char *initial_branch, int quiet);
 
 /*
  * NOTE NOTE NOTE!!

2.43.GIT

There is a topic in-flight that introduces the .compat_hash_algo member to the repo_fmt structure. Seeing a conflict resolution like the attached (there are many others that are similar in spirit), I have to wonder if we want to add repo_set_ref_storage_format() helper function. There are many assignments to .ref_storage_format member after this series is applied.

Note that I haven't read the series in full, so take the above with a grain of salt---it might turn out to be that direct assignment is more desirable, I dunno.

Thanks.

diff --cc setup.c
index 2f4571c12a,5038e78cdd..0000000000
@@@ ...
@@@ -1584,8 -1577,8 +1595,10 @@@ const char *setup_git_directory_gently(
  		}
  		if (startup_info->have_repository) {
  			repo_set_hash_algo(the_repository, repo_fmt.hash_algo);
 +			repo_set_compat_hash_algo(the_repository,
 +						  repo_fmt.compat_hash_algo);
+ 			the_repository->ref_storage_format =
+ 				repo_fmt.ref_storage_format;
  			the_repository->repository_format_worktree_config =
  				repo_fmt.worktree_config;
  			/* take ownership of repo_fmt.partial_clone */

Wrapping this in a repo_set_ref_storage_format() doesn't add much for now, but on the other hand it also doesn't hurt and is more in line with how we set the other formats. This could also be useful in the future to have a central place for additional sanity checks, if required. So yeah, let's do it.

Makes me wonder whether we should then also add the following diff to "setup: set repository's format on init" when both topics are being merged together:

index 3d980814bc..3d35c78c68 100644
@@ -2210,6 +2210,7 @@ int init_db(const char *git_dir, const char *real_git_dir,
 	 * format we can update the repository's settings accordingly.
 	 */
 	repo_set_hash_algo(the_repository, repo_fmt.hash_algo);
+	repo_set_compat_hash_algo(the_repository, repo_fmt.compat_hash_algo);
 	repo_set_ref_storage_format(the_repository, repo_fmt.ref_storage_format);
 
 	if (!(flags & INIT_DB_SKIP_REFDB))

Patrick

Well, the above code is newly added by my series to ensure that init_db() results in a properly initialized repo upon return. So the compat hash algo series cannot yet call repo_set_compat_hash_algo() because the code site doesn't exist, whereas my series cannot yet add the call because there is no compat hash algo yet.

So depending on which series lands first we'll either have to adapt the respective other series or do an evil merge.

Patrick

Nit: s/erorr/error

No, it's a leftover from a previous iteration. Will drop.

Patrick

The proper hash algorithm and ref storage format that will be used for a newly initialized repository will be figured out in init_db() via validate_hash_algorithm() and validate_ref_storage_format(). Until now though, we never set up the hash algorithm or ref storage format of the_repository accordingly.

There are only two callsites of init_db(), one in git-init(1) and one in git-clone(1). The former function doesn't care for the formats to be set up properly because it never access the repository after calling the function in the first place.

For git-clone(1) it's a different story though, as we call init_db() before listing remote refs. While we do indeed have the wrong hash function in the_repository when init_db() sets up a non-default object format for the repository, it never mattered because we adjust the hash after learning about the remote's hash function via the listed refs.

So the current state is correct for the hash algo, but it's not for the ref storage format because git-clone(1) wouldn't know to set it up properly. But instead of adjusting only the ref_storage_format, set both the hash algo and the ref storage format so that the_repository is in the correct state when init_db() exits. This is fine as we will adjust the hash later on anyway and makes it easier to reason about the end state of the_repository.

---
 setup.c | 7 +++++++
 1 file changed, 7 insertions(+)

index c1bf106379..5dffea6e2f 100644
@@ -2203,6 +2203,13 @@ int init_db(const char *git_dir, const char *real_git_dir,
 				      &repo_fmt, prev_bare_repository,
 				      init_shared_repository);
 
+	/*
+	 * Now that we have set up both the hash algorithm and the ref storage
+	 * format we can update the repository's settings accordingly.
+	 */
+	the_repository->hash_algo = &hash_algos[repo_fmt.hash_algo];
+	the_repository->ref_storage_format = repo_fmt.ref_storage_format;
+
 	if (!(flags & INIT_DB_SKIP_REFDB))
 		create_reference_database(repo_fmt.ref_storage_format,
 					  initial_branch, flags & INIT_DB_QUIET);

2.43.GIT

Introduce a new "extensions.refStorage" extension that allows us to specify the ref storage format used by a repository. For now, the only supported format is the "files" format, but this list will likely soon be extended to also support the upcoming "reftable" format.

There have been discussions on the Git mailing list in the past around how exactly this extension should look like. One alternative [1] that was discussed was whether it would make sense to model the extension in such a way that backends are arbitrarily stackable. This would allow for a combined value of e.g. "loose,packed-refs" or "loose,reftable", which indicates that new refs would be written via "loose" files backend and compressed into "packed-refs" or "reftable" backends, respectively.

It is arguable though whether this flexibility and the complexity that it brings with it is really required for now. It is not foreseeable that there will be a proliferation of backends in the near-term future, and the current set of existing formats and formats which are on the horizon can easily be configured with the much simpler proposal where we have a single value, only.

Furthermore, if we ever see that we indeed want to gain the ability to arbitrarily stack the ref formats, then we can adapt the current extension rather easily. Given that Git clients will refuse any unknown value for the "extensions.refStorage" extension they would also know to ignore a stacked "loose,packed-refs" in the future.

So let's stick with the easy proposal for the time being and wire up the extension.

[1]: <[email protected]>

---
 Documentation/config/extensions.txt           | 11 ++++++++
 Documentation/ref-storage-format.txt          |  1 +
 .../technical/repository-version.txt          |  5 ++++
 builtin/clone.c                               |  2 +-
 setup.c                                       | 23 +++++++++++++---
 setup.h                                       |  3 ++-
 t/t0001-init.sh                               | 26 +++++++++++++++++++
 t/test-lib.sh                                 |  2 +-
 8 files changed, 67 insertions(+), 6 deletions(-)
 create mode 100644 Documentation/ref-storage-format.txt

index bccaec7a96..66db0e15da 100644
@@ -7,6 +7,17 @@ Note that this setting should only be set by linkgit:git-init[1] or
 linkgit:git-clone[1].  Trying to change it after initialization will not
 work and will produce hard-to-diagnose issues.
 
+extensions.refStorage::
+	Specify the ref storage format to use. The acceptable values are:
++
+include::../ref-storage-format.txt[]
++
+It is an error to specify this key unless `core.repositoryFormatVersion` is 1.
++
+Note that this setting should only be set by linkgit:git-init[1] or
+linkgit:git-clone[1]. Trying to change it after initialization will not
+work and will produce hard-to-diagnose issues.
+
 extensions.worktreeConfig::
 	If enabled, then worktrees will load config settings from the
 	`$GIT_DIR/config.worktree` file in addition to the

new file mode 100644
index 0000000000..1a65cac468
@@ -0,0 +1 @@
+* `files` for loose files with packed-refs. This is the default.

index 045a76756f..27be3741e6 100644
@@ -100,3 +100,8 @@ If set, by default "git config" reads from both "config" and
 multiple working directory mode, "config" file is shared while
 "config.worktree" is per-working directory (i.e., it's in
 GIT_COMMON_DIR/worktrees/<id>/config.worktree)
+
+==== `refStorage`
+
+Specifies the file format for the ref database. The only valid value
+is `files` (loose references with a packed-refs file).

index 6840064b59..20c161e94a 100644
@@ -1289,7 +1289,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	 * ours to the same thing.
 	 */
 	hash_algo = hash_algo_by_ptr(transport_get_hash_algo(transport));
-	initialize_repository_version(hash_algo, 1);
+	initialize_repository_version(hash_algo, the_repository->ref_storage_format, 1);
 	repo_set_hash_algo(the_repository, hash_algo);
 	create_reference_database(the_repository->ref_storage_format, NULL, 1);
 

index 5dffea6e2f..7eb4ae8ea0 100644
@@ -590,6 +590,17 @@ static enum extension_result handle_extension(const char *var,
 				     "extensions.objectformat", value);
 		data->hash_algo = format;
 		return EXTENSION_OK;
+	} else if (!strcmp(ext, "refstorage")) {
+		int format;
+
+		if (!value)
+			return config_error_nonbool(var);
+		format = ref_storage_format_by_name(value);
+		if (format == REF_STORAGE_FORMAT_UNKNOWN)
+			return error(_("invalid value for '%s': '%s'"),
+				     "extensions.refstorage", value);
+		data->ref_storage_format = format;
+		return EXTENSION_OK;
 	}
 	return EXTENSION_UNKNOWN;
 }

@@ -1869,12 +1880,14 @@ static int needs_work_tree_config(const char *git_dir, const char *work_tree)
 	return 1;
 }
 
-void initialize_repository_version(int hash_algo, int reinit)
+void initialize_repository_version(int hash_algo, int ref_storage_format,
+				   int reinit)
 {
 	char repo_version_string[10];
 	int repo_version = GIT_REPO_VERSION;
 
-	if (hash_algo != GIT_HASH_SHA1)
+	if (hash_algo != GIT_HASH_SHA1 ||
+	    ref_storage_format != REF_STORAGE_FORMAT_FILES)
 		repo_version = GIT_REPO_VERSION_READ;
 
 	/* This forces creation of new config file */

@@ -1887,6 +1900,10 @@ void initialize_repository_version(int hash_algo, int reinit)
 			       hash_algos[hash_algo].name);
 	else if (reinit)
 		git_config_set_gently("extensions.objectformat", NULL);
+
+	if (ref_storage_format != REF_STORAGE_FORMAT_FILES)
+		git_config_set("extensions.refstorage",
+			       ref_storage_format_to_name(ref_storage_format));
 }
 
 static int is_reinit(void)

@@ -2028,7 +2045,7 @@ static int create_default_files(const char *template_path,
 		adjust_shared_perm(get_git_dir());
 	}
 
-	initialize_repository_version(fmt->hash_algo, 0);
+	initialize_repository_version(fmt->hash_algo, fmt->ref_storage_format, 0);
 
 	/* Check filemode trustability */
 	path = git_path_buf(&buf, "config");

index 4927abf2cf..89033ae1d9 100644
@@ -180,7 +180,8 @@ int init_db(const char *git_dir, const char *real_git_dir,
 	    int ref_storage_format,
 	    const char *initial_branch, int init_shared_repository,
 	    unsigned int flags);
-void initialize_repository_version(int hash_algo, int reinit);
+void initialize_repository_version(int hash_algo, int ref_storage_format,
+				   int reinit);
 void create_reference_database(int ref_storage_format,
 			       const char *initial_branch, int quiet);
 

index 2b78e3be47..38b3e4c39e 100755
@@ -532,6 +532,32 @@ test_expect_success 'init rejects attempts to initialize with different hash' '
 	test_must_fail git -C sha256 init --object-format=sha1
 '
 
+test_expect_success DEFAULT_REPO_FORMAT 'extensions.refStorage is not allowed with repo version 0' '
+	test_when_finished "rm -rf refstorage" &&
+	git init refstorage &&
+	git -C refstorage config extensions.refStorage files &&
+	test_must_fail git -C refstorage rev-parse 2>err &&
+	grep "repo version is 0, but v1-only extension found" err
+'
+
+test_expect_success DEFAULT_REPO_FORMAT 'extensions.refStorage with files backend' '
+	test_when_finished "rm -rf refstorage" &&
+	git init refstorage &&
+	git -C refstorage config core.repositoryformatversion 1 &&
+	git -C refstorage config extensions.refStorage files &&
+	test_commit -C refstorage A &&
+	git -C refstorage rev-parse --verify HEAD
+'
+
+test_expect_success DEFAULT_REPO_FORMAT 'extensions.refStorage with unknown backend' '
+	test_when_finished "rm -rf refstorage" &&
+	git init refstorage &&
+	git -C refstorage config core.repositoryformatversion 1 &&
+	git -C refstorage config extensions.refStorage garbage &&
+	test_must_fail git -C refstorage rev-parse 2>err &&
+	grep "invalid value for ${SQ}extensions.refstorage${SQ}: ${SQ}garbage${SQ}" err
+'
+
 test_expect_success MINGW 'core.hidedotfiles = false' '
 	git config --global core.hidedotfiles false &&
 	rm -rf newdir &&

index dc03f06b8e..4685cc3d48 100644
@@ -1937,7 +1937,7 @@ test_lazy_prereq SHA1 '
 '
 
 test_lazy_prereq DEFAULT_REPO_FORMAT '
-	test_have_prereq SHA1
+	test_have_prereq SHA1,REFFILES
 '
 
 # Ensure that no test accidentally triggers a Git command

2.43.GIT

Introduce a new GIT_DEFAULT_REF_FORMAT environment variable that lets users control the default ref format used by both git-init(1) and git-clone(1). This is modeled after GIT_DEFAULT_OBJECT_FORMAT, which does the same thing for the repository's object format.

---
 Documentation/git.txt |  5 +++++
 setup.c               |  7 +++++++
 t/t0001-init.sh       | 18 ++++++++++++++++++
 3 files changed, 30 insertions(+)

index 4698d7a42b..0ab19eef3b 100644
@@ -556,6 +556,11 @@ double-quotes and respecting backslash escapes. E.g., the value
 	is always used. The default is "sha1".
 	See `--object-format` in linkgit:git-init[1].
 
+`GIT_DEFAULT_REF_FORMAT`::
+	If this variable is set, the default reference backend format for new
+	repositories will be set to this value. The default is "files".
+	See `--ref-format` in linkgit:git-init[1].
+
 Git Commits
 ~~~~~~~~~~~
 `GIT_AUTHOR_NAME`::

index 7eb4ae8ea0..8913e30974 100644
@@ -2160,12 +2160,19 @@ static void validate_hash_algorithm(struct repository_format *repo_fmt, int hash
 
 static void validate_ref_storage_format(struct repository_format *repo_fmt, int format)
 {
+	const char *name = getenv("GIT_DEFAULT_REF_FORMAT");
+
 	if (repo_fmt->version >= 0 &&
 	    format != REF_STORAGE_FORMAT_UNKNOWN &&
 	    format != repo_fmt->ref_storage_format) {
 		die(_("attempt to reinitialize repository with different reference storage format"));
 	} else if (format != REF_STORAGE_FORMAT_UNKNOWN) {
 		repo_fmt->ref_storage_format = format;
+	} else if (name) {
+		format = ref_storage_format_by_name(name);
+		if (format == REF_STORAGE_FORMAT_UNKNOWN)
+			die(_("unknown ref storage format '%s'"), name);
+		repo_fmt->ref_storage_format = format;
 	}
 }
 

index 38b3e4c39e..30ce752cc1 100755
@@ -558,6 +558,24 @@ test_expect_success DEFAULT_REPO_FORMAT 'extensions.refStorage with unknown back
 	grep "invalid value for ${SQ}extensions.refstorage${SQ}: ${SQ}garbage${SQ}" err
 '
 
+test_expect_success DEFAULT_REPO_FORMAT 'init with GIT_DEFAULT_REF_FORMAT=files' '
+	test_when_finished "rm -rf refformat" &&
+	GIT_DEFAULT_REF_FORMAT=files git init refformat &&
+	echo 0 >expect &&
+	git -C refformat config core.repositoryformatversion >actual &&
+	test_cmp expect actual &&
+	test_must_fail git -C refformat config extensions.refstorage
+'
+
+test_expect_success 'init with GIT_DEFAULT_REF_FORMAT=garbage' '
+	test_when_finished "rm -rf refformat" &&
+	cat >expect <<-EOF &&
+	fatal: unknown ref storage format ${SQ}garbage${SQ}
+	EOF
+	test_must_fail env GIT_DEFAULT_REF_FORMAT=garbage git init refformat 2>err &&
+	test_cmp expect err
+'
+
 test_expect_success MINGW 'core.hidedotfiles = false' '
 	git config --global core.hidedotfiles false &&
 	rm -rf newdir &&

2.43.GIT

Introduce a new GIT_TEST_DEFAULT_REF_FORMAT environment variable that lets developers run the test suite with a different default ref format without impacting the ref format used by non-test Git invocations. This is modeled after GIT_TEST_DEFAULT_OBJECT_FORMAT, which does the same thing for the repository's object format.

Adapt the setup of the REFFILES test prerequisite to be conditionally set based on the default ref format.

---
 t/README                |  3 +++
 t/test-lib-functions.sh |  5 +++++
 t/test-lib.sh           | 11 ++++++++++-
 3 files changed, 18 insertions(+), 1 deletion(-)

index 36463d0742..621d3b8c09 100644
@@ -479,6 +479,9 @@ GIT_TEST_DEFAULT_HASH=<hash-algo> specifies which hash algorithm to
 use in the test scripts. Recognized values for <hash-algo> are "sha1"
 and "sha256".
 
+GIT_TEST_DEFAULT_REF_FORMAT=<format> specifies which ref storage format
+to use in the test scripts. Recognized values for <format> are "files".
+
 GIT_TEST_NO_WRITE_REV_INDEX=<boolean>, when true disables the
 'pack.writeReverseIndex' setting.
 

index 03292602fb..61871b2a3b 100644
@@ -1659,6 +1659,11 @@ test_detect_hash () {
 	test_hash_algo="${GIT_TEST_DEFAULT_HASH:-sha1}"
 }
 
+# Detect the hash algorithm in use.
+test_detect_ref_format () {
+	echo "${GIT_TEST_DEFAULT_REF_FORMAT:-files}"
+}
+
 # Load common hash metadata and common placeholder object IDs for use with
 # test_oid.
 test_oid_init () {

index 4685cc3d48..fc93aa57e6 100644
@@ -542,6 +542,8 @@ export EDITOR
 
 GIT_DEFAULT_HASH="${GIT_TEST_DEFAULT_HASH:-sha1}"
 export GIT_DEFAULT_HASH
+GIT_DEFAULT_REF_FORMAT="${GIT_TEST_DEFAULT_REF_FORMAT:-files}"
+export GIT_DEFAULT_REF_FORMAT
 GIT_TEST_MERGE_ALGORITHM="${GIT_TEST_MERGE_ALGORITHM:-ort}"
 export GIT_TEST_MERGE_ALGORITHM
 

@@ -1745,7 +1747,14 @@ parisc* | hppa*)
 	;;
 esac
 
-test_set_prereq REFFILES
+case "$GIT_DEFAULT_REF_FORMAT" in
+files)
+	test_set_prereq REFFILES;;
+*)
+	echo 2>&1 "error: unknown ref format $GIT_DEFAULT_REF_FORMAT"
+	exit 1
+	;;
+esac
 
 ( COLUMNS=1 && test $COLUMNS = 1 ) && test_set_prereq COLUMNS_CAN_BE_1
 test -z "$NO_CURL" && test_set_prereq LIBCURL

2.43.GIT

Introduce a new --show-ref-format to git-rev-parse(1) that causes it to print the ref format used by a repository.

---
 Documentation/git-rev-parse.txt |  3 +++
 builtin/rev-parse.c             |  4 ++++
 t/t1500-rev-parse.sh            | 17 +++++++++++++++++
 3 files changed, 24 insertions(+)

index 912fab9f5e..546faf9017 100644
@@ -307,6 +307,9 @@ The following options are unaffected by `--path-format`:
 	input, multiple algorithms may be printed, space-separated.
 	If not specified, the default is "storage".
 
+--show-ref-format::
+	Show the reference storage format used for the repository.
+
 
 Other Options
 ~~~~~~~~~~~~~

index fde8861ca4..99725a6ff1 100644
@@ -1059,6 +1059,10 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 				puts(the_hash_algo->name);
 				continue;
 			}
+			if (!strcmp(arg, "--show-ref-format")) {
+				puts(ref_storage_format_to_name(the_repository->ref_storage_format));
+				continue;
+			}
 			if (!strcmp(arg, "--end-of-options")) {
 				seen_end_of_options = 1;
 				if (filter & (DO_FLAGS | DO_REVS))

index 3f9e7f62e4..a669e592f1 100755
@@ -208,6 +208,23 @@ test_expect_success 'rev-parse --show-object-format in repo' '
 	grep "unknown mode for --show-object-format: squeamish-ossifrage" err
 '
 
+test_expect_success 'rev-parse --show-ref-format' '
+	test_detect_ref_format >expect &&
+	git rev-parse --show-ref-format >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rev-parse --show-ref-format with invalid storage' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		git config extensions.refstorage broken &&
+		test_must_fail git rev-parse --show-ref-format 2>err &&
+		grep "error: invalid value for ${SQ}extensions.refstorage${SQ}: ${SQ}broken${SQ}" err
+	)
+'
+
 test_expect_success '--show-toplevel from subdir of working tree' '
 	pwd >expect &&
 	git -C sub/dir rev-parse --show-toplevel >actual &&

2.43.GIT

Introduce a new --ref-format value flag for git-init(1) that allows the user to specify the ref format that is to be used for a newly initialized repository.

---
 Documentation/git-init.txt |  7 +++++++
 builtin/init-db.c          | 13 ++++++++++++-
 t/t0001-init.sh            | 26 ++++++++++++++++++++++++++
 3 files changed, 45 insertions(+), 1 deletion(-)

index 6f0d2973bf..e8dc645bb5 100644
@@ -11,6 +11,7 @@ SYNOPSIS
 [verse]
 'git init' [-q | --quiet] [--bare] [--template=<template-directory>]
 	  [--separate-git-dir <git-dir>] [--object-format=<format>]
+	  [--ref-format=<format>]
 	  [-b <branch-name> | --initial-branch=<branch-name>]
 	  [--shared[=<permissions>]] [<directory>]
 

@@ -57,6 +58,12 @@ values are 'sha1' and (if enabled) 'sha256'.  'sha1' is the default.
 +
 include::object-format-disclaimer.txt[]
 
+--ref-format=<format>::
+
+Specify the given ref storage format for the repository. The valid values are:
++
+include::ref-storage-format.txt[]
+
 --template=<template-directory>::
 
 Specify the directory from which templates will be used.  (See the "TEMPLATE

index b6e80feab6..770b2822fe 100644
@@ -58,6 +58,7 @@ static int shared_callback(const struct option *opt, const char *arg, int unset)
 static const char *const init_db_usage[] = {
 	N_("git init [-q | --quiet] [--bare] [--template=<template-directory>]\n"
 	   "         [--separate-git-dir <git-dir>] [--object-format=<format>]\n"
+	   "         [--ref-format=<format>]\n"
 	   "         [-b <branch-name> | --initial-branch=<branch-name>]\n"
 	   "         [--shared[=<permissions>]] [<directory>]"),
 	NULL

@@ -77,8 +78,10 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 	const char *template_dir = NULL;
 	unsigned int flags = 0;
 	const char *object_format = NULL;
+	const char *ref_format = NULL;
 	const char *initial_branch = NULL;
 	int hash_algo = GIT_HASH_UNKNOWN;
+	int ref_storage_format = REF_STORAGE_FORMAT_UNKNOWN;
 	int init_shared_repository = -1;
 	const struct option init_db_options[] = {
 		OPT_STRING(0, "template", &template_dir, N_("template-directory"),

@@ -96,6 +99,8 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 			   N_("override the name of the initial branch")),
 		OPT_STRING(0, "object-format", &object_format, N_("hash"),
 			   N_("specify the hash algorithm to use")),
+		OPT_STRING(0, "ref-format", &ref_format, N_("format"),
+			   N_("specify the reference format to use")),
 		OPT_END()
 	};
 

@@ -159,6 +164,12 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 			die(_("unknown hash algorithm '%s'"), object_format);
 	}
 
+	if (ref_format) {
+		ref_storage_format = ref_storage_format_by_name(ref_format);
+		if (ref_storage_format == REF_STORAGE_FORMAT_UNKNOWN)
+			die(_("unknown ref storage format '%s'"), ref_format);
+	}
+
 	if (init_shared_repository != -1)
 		set_shared_repository(init_shared_repository);
 

@@ -237,6 +248,6 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 
 	flags |= INIT_DB_EXIST_OK;
 	return init_db(git_dir, real_git_dir, template_dir, hash_algo,
-		       REF_STORAGE_FORMAT_UNKNOWN, initial_branch,
+		       ref_storage_format, initial_branch,
 		       init_shared_repository, flags);
 }

index 30ce752cc1..b131d665db 100755
@@ -576,6 +576,32 @@ test_expect_success 'init with GIT_DEFAULT_REF_FORMAT=garbage' '
 	test_cmp expect err
 '
 
+test_expect_success 'init with --ref-format=files' '
+	test_when_finished "rm -rf refformat" &&
+	git init --ref-format=files refformat &&
+	echo files >expect &&
+	git -C refformat rev-parse --show-ref-format >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 're-init with same format' '
+	test_when_finished "rm -rf refformat" &&
+	git init --ref-format=files refformat &&
+	git init --ref-format=files refformat &&
+	echo files >expect &&
+	git -C refformat rev-parse --show-ref-format >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'init with --ref-format=garbage' '
+	test_when_finished "rm -rf refformat" &&
+	cat >expect <<-EOF &&
+	fatal: unknown ref storage format ${SQ}garbage${SQ}
+	EOF
+	test_must_fail git init --ref-format=garbage refformat 2>err &&
+	test_cmp expect err
+'
+
 test_expect_success MINGW 'core.hidedotfiles = false' '
 	git config --global core.hidedotfiles false &&
 	rm -rf newdir &&

2.43.GIT

Introduce a new --ref-format value flag for git-clone(1) that allows the user to specify the ref format that is to be used for a newly initialized repository.

---
 Documentation/git-clone.txt |  6 ++++++
 builtin/clone.c             | 12 +++++++++++-
 t/t5601-clone.sh            | 17 +++++++++++++++++
 3 files changed, 34 insertions(+), 1 deletion(-)

index c37c4a37f7..6e43eb9c20 100644
@@ -311,6 +311,12 @@ or `--mirror` is given)
 	The result is Git repository can be separated from working
 	tree.
 
+--ref-format=<ref-format::
+
+Specify the given ref storage format for the repository. The valid values are:
++
+include::ref-storage-format.txt[]
+
 -j <n>::
 --jobs <n>::
 	The number of submodules fetched at the same time.

index 20c161e94a..b635bbcb43 100644
@@ -72,6 +72,7 @@ static char *remote_name = NULL;
 static char *option_branch = NULL;
 static struct string_list option_not = STRING_LIST_INIT_NODUP;
 static const char *real_git_dir;
+static const char *ref_format;
 static char *option_upload_pack = "git-upload-pack";
 static int option_verbosity;
 static int option_progress = -1;

@@ -157,6 +158,8 @@ static struct option builtin_clone_options[] = {
 		    N_("any cloned submodules will be shallow")),
 	OPT_STRING(0, "separate-git-dir", &real_git_dir, N_("gitdir"),
 		   N_("separate git dir from working tree")),
+	OPT_STRING(0, "ref-format", &ref_format, N_("format"),
+		   N_("specify the reference format to use")),
 	OPT_STRING_LIST('c', "config", &option_config, N_("key=value"),
 			N_("set config inside the new repository")),
 	OPT_STRING_LIST(0, "server-option", &server_options,

@@ -930,6 +933,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	int submodule_progress;
 	int filter_submodules = 0;
 	int hash_algo;
+	int ref_storage_format = REF_STORAGE_FORMAT_UNKNOWN;
 	const int do_not_override_repo_unix_permissions = -1;
 
 	struct transport_ls_refs_options transport_ls_refs_options =

@@ -955,6 +959,12 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	if (option_single_branch == -1)
 		option_single_branch = deepen ? 1 : 0;
 
+	if (ref_format) {
+		ref_storage_format = ref_storage_format_by_name(ref_format);
+		if (ref_storage_format == REF_STORAGE_FORMAT_UNKNOWN)
+			die(_("unknown ref storage format '%s'"), ref_format);
+	}
+
 	if (option_mirror)
 		option_bare = 1;
 

@@ -1106,7 +1116,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	 * their on-disk data structures.
 	 */
 	init_db(git_dir, real_git_dir, option_template, GIT_HASH_UNKNOWN,
-		REF_STORAGE_FORMAT_UNKNOWN, NULL,
+		ref_storage_format, NULL,
 		do_not_override_repo_unix_permissions, INIT_DB_QUIET | INIT_DB_SKIP_REFDB);
 
 	if (real_git_dir) {

index 47eae641f0..fb1b9c686d 100755
@@ -157,6 +157,23 @@ test_expect_success 'clone --mirror does not repeat tags' '
 
 '
 
+test_expect_success 'clone with files ref format' '
+	test_when_finished "rm -rf ref-storage" &&
+	git clone --ref-format=files --mirror src ref-storage &&
+	echo files >expect &&
+	git -C ref-storage rev-parse --show-ref-format >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'clone with garbage ref format' '
+	cat >expect <<-EOF &&
+	fatal: unknown ref storage format ${SQ}garbage${SQ}
+	EOF
+	test_must_fail git clone --ref-format=garbage --mirror src ref-storage 2>err &&
+	test_cmp expect err &&
+	test_path_is_missing ref-storage
+'
+
 test_expect_success 'clone to destination with trailing /' '
 
 	git clone src target-1/ &&

2.43.GIT

In t9500 we're writing a custom configuration that sets up gitweb. This requires us manually ensure that the repository format is configured as required, including both the repository format version and extensions. With the introduction of the "extensions.refStorage" extension we need to update the test to also write this new one.

---
 t/t9500-gitweb-standalone-no-errors.sh | 5 +++++
 1 file changed, 5 insertions(+)

index 0333065d4d..7679780fb8 100755
@@ -627,6 +627,7 @@ test_expect_success \
 test_expect_success 'setup' '
 	version=$(git config core.repositoryformatversion) &&
 	algo=$(test_might_fail git config extensions.objectformat) &&
+	refstorage=$(test_might_fail git config extensions.refstorage) &&
 	cat >.git/config <<-\EOF &&
 	# testing noval and alternate separator
 	[gitweb]

@@ -637,6 +638,10 @@ test_expect_success 'setup' '
 	if test -n "$algo"
 	then
 		git config extensions.objectformat "$algo"
+	fi &&
+	if test -n "$refstorage"
+	then
+		git config extensions.refstorage "$refstorage"
 	fi
 '
 

2.43.GIT

Nit: s/requires us/requires us to/

Hello,

Apart from small nits, the series looks good to me, thanks!

Thanks. Hopefully we can merge it down after a quick, small, and final reroll?

Hi,

this is the second version of my patch series that introduces the new refStorage extension. This extension will be used for the upcoming reftable backend.

Changes compared to v2:

- Fixed various typos in commit messages.

- Fixed redundant information when the refstorage extension's value isn't understood.

- Introduced repo_set_ref_storage_format().

Thanks for the feedback so far!

Patrick

Patrick Steinhardt (12):
t: introduce DEFAULT_REPO_FORMAT prereq
worktree: skip reading HEAD when repairing worktrees
refs: refactor logic to look up storage backends
setup: start tracking ref storage format
setup: set repository's formats on init
setup: introduce "extensions.refStorage" extension
setup: introduce GIT_DEFAULT_REF_FORMAT envvar
t: introduce GIT_TEST_DEFAULT_REF_FORMAT envvar builtin/rev-parse: introduce --show-ref-format flag builtin/init: introduce --ref-format= value flag builtin/clone: introduce --ref-format= value flag
t9500: write "extensions.refstorage" into config

 Documentation/config/extensions.txt           | 11 +++
 Documentation/git-clone.txt                   |  6 ++
 Documentation/git-init.txt                    |  7 ++
 Documentation/git-rev-parse.txt               |  3 +
 Documentation/git.txt                         |  5 ++
 Documentation/ref-storage-format.txt          |  1 +
 .../technical/repository-version.txt          |  5 ++
 builtin/clone.c                               | 17 ++++-
 builtin/init-db.c                             | 15 +++-
 builtin/rev-parse.c                           |  4 ++
 refs.c                                        | 34 ++++++---
 refs.h                                        |  3 +
 refs/debug.c                                  |  1 -
 refs/files-backend.c                          |  1 -
 refs/packed-backend.c                         |  1 -
 refs/refs-internal.h                          |  1 -
 repository.c                                  |  6 ++
 repository.h                                  |  7 ++
 setup.c                                       | 63 +++++++++++++++--
 setup.h                                       |  9 ++-
 t/README                                      |  3 +
 t/t0001-init.sh                               | 70 +++++++++++++++++++
 t/t1500-rev-parse.sh                          | 17 +++++
 t/t3200-branch.sh                             |  2 +-
 t/t5601-clone.sh                              | 17 +++++
 t/t9500-gitweb-standalone-no-errors.sh        |  5 ++
 t/test-lib-functions.sh                       |  5 ++
 t/test-lib.sh                                 | 15 +++-
 worktree.c                                    | 24 ++++---
 29 files changed, 323 insertions(+), 35 deletions(-)
 create mode 100644 Documentation/ref-storage-format.txt

Range-diff against v1:
1: 239ca38efd ! 1: 3613439cb7 t: introduce DEFAULT_REPO_FORMAT prereq
@@ Commit message
repository format or otherwise they would fail to run, e.g. because they fail to detect the correct hash function. While the hash function is the only extension right now that creates problems like this, we are about
- to add a second extensions for the ref format.
+ to add a second extension for the ref format.

Introduce a new DEFAULT_REPO_FORMAT prereq that can easily be amended whenever we add new format extensions. Next to making any such changes
2: e895091025 ! 2: ecf4f1ddee worktree: skip reading HEAD when repairing worktrees
@@ Commit message
worktree: skip reading HEAD when repairing worktrees

When calling git init --separate-git-dir=<new-path> on a preexisting
- repository, then we move the Git directory of that repository to the new
- path specified by the user. If there are worktrees present in the Git
- repository, we need to repair the worktrees so that their gitlinks point
- to the new location of the repository.
+ repository, we move the Git directory of that repository to the new path
+ specified by the user. If there are worktrees present in the repository,
+ we need to repair the worktrees so that their gitlinks point to the new
+ location of the repository.

This repair logic will load repositories via get_worktrees(), which will enumerate up and initialize all worktrees. Part of initialization
@@ Commit message
format, which does not work.

We do not require the worktree HEADs at all to repair worktrees. So
- let's fix issue this by skipping over the step that reads them.
+ let's fix this issue by skipping over the step that reads them.

3: f712d5ef5b ! 3: 12329b99b7 refs: refactor logic to look up storage backends

    @@ refs.c
     -	for (be = refs_backends; be; be = be->next)
     -		if (!strcmp(be->name, name))
     -			return be;
    -+	if (ref_storage_format && ref_storage_format < ARRAY_SIZE(refs_backends))
    ++	if (ref_storage_format < ARRAY_SIZE(refs_backends))
     +		return refs_backends[ref_storage_format];
      	return NULL;
      }
    @@ refs.c: static struct ref_store *ref_store_init(struct repository *repo,
      
      	if (!be)
     -		BUG("reference backend %s is unknown", be_name);
    -+		BUG("reference backend %s is unknown", ref_storage_format_to_name(format));
    ++		BUG("reference backend is unknown");
      
      	refs = be->init(repo, gitdir, flags);
      	return refs;
 4:  6564659d40 !  4:  ddd099fbaf setup: start tracking ref storage format when
    @@ Metadata
     Author: Patrick Steinhardt <[email protected]>
     
      ## Commit message ##
    -    setup: start tracking ref storage format when
    +    setup: start tracking ref storage format
     
         In order to discern which ref storage format a repository is supposed to
         use we need to start setting up and/or discovering the format. This
    @@ Commit message
           - The first path is when we create a repository via `init_db()`. When
             we are re-initializing a preexisting repository we need to retain
             the previously used ref storage format -- if the user asked for a
    -        different format then this indicates an erorr and we error out.
    +        different format then this indicates an error and we error out.
             Otherwise we either initialize the repository with the format asked
             for by the user or the default format, which currently is the
             "files" backend.
    @@ refs.c: static struct ref_store *ref_store_init(struct repository *repo,
      
     +	be = find_ref_storage_backend(repo->ref_storage_format);
      	if (!be)
    --		BUG("reference backend %s is unknown", ref_storage_format_to_name(format));
    -+		BUG("reference backend is unknown");
    - 
    - 	refs = be->init(repo, gitdir, flags);
    - 	return refs;
    -
    - ## refs.h ##
    -@@ refs.h: struct string_list;
    - struct string_list_item;
    - struct worktree;
    - 
    -+int default_ref_storage_format(void);
    - int ref_storage_format_by_name(const char *name);
    - const char *ref_storage_format_to_name(int ref_storage_format);
    + 		BUG("reference backend is unknown");
      
     
      ## repository.c ##
    +@@ repository.c: void repo_set_hash_algo(struct repository *repo, int hash_algo)
    + 	repo->hash_algo = &hash_algos[hash_algo];
    + }
    + 
    ++void repo_set_ref_storage_format(struct repository *repo, int format)
    ++{
    ++	repo->ref_storage_format = format;
    ++}
    ++
    + /*
    +  * Attempt to resolve and set the provided 'gitdir' for repository 'repo'.
    +  * Return 0 upon success and a non-zero value upon failure.
     @@ repository.c: int repo_init(struct repository *repo,
      		goto error;
      
      	repo_set_hash_algo(repo, format.hash_algo);
    -+	repo->ref_storage_format = format.ref_storage_format;
    ++	repo_set_ref_storage_format(repo, format.ref_storage_format);
      	repo->repository_format_worktree_config = format.worktree_config;
      
      	/* take ownership of format.partial_clone */
    @@ repository.h: struct repository {
      	/* A unique-id for tracing purposes. */
      	int trace2_repo_id;
      
    +@@ repository.h: void repo_set_gitdir(struct repository *repo, const char *root,
    + 		     const struct set_gitdir_args *extra_args);
    + void repo_set_worktree(struct repository *repo, const char *path);
    + void repo_set_hash_algo(struct repository *repo, int algo);
    ++void repo_set_ref_storage_format(struct repository *repo, int format);
    + void initialize_the_repository(void);
    + RESULT_MUST_BE_USED
    + int repo_init(struct repository *r, const char *gitdir, const char *worktree);
     
      ## setup.c ##
     @@ setup.c: const char *setup_git_directory_gently(int *nongit_ok)
      		}
      		if (startup_info->have_repository) {
      			repo_set_hash_algo(the_repository, repo_fmt.hash_algo);
    -+			the_repository->ref_storage_format =
    -+				repo_fmt.ref_storage_format;
    ++			repo_set_ref_storage_format(the_repository,
    ++						    repo_fmt.ref_storage_format);
      			the_repository->repository_format_worktree_config =
      				repo_fmt.worktree_config;
      			/* take ownership of repo_fmt.partial_clone */
    @@ setup.c: void check_repository_format(struct repository_format *fmt)
      	check_repository_format_gently(get_git_dir(), fmt, NULL);
      	startup_info->have_repository = 1;
      	repo_set_hash_algo(the_repository, fmt->hash_algo);
    -+	the_repository->ref_storage_format =
    -+		fmt->ref_storage_format;
    ++	repo_set_ref_storage_format(the_repository,
    ++				    fmt->ref_storage_format);
      	the_repository->repository_format_worktree_config =
      		fmt->worktree_config;
      	the_repository->repository_format_partial_clone =
    @@ setup.c: void create_reference_database(const char *initial_branch, int quiet)
      	safe_create_dir(git_path("refs"), 1);
      	adjust_shared_perm(git_path("refs"));
      
    -+	the_repository->ref_storage_format = ref_storage_format;
    ++	repo_set_ref_storage_format(the_repository, ref_storage_format);
      	if (refs_init_db(&err))
      		die("failed to set up refs db: %s", err.buf);

5: f90a63d63c ! 5: 01a1e58a97 setup: set repository's formats on init

    @@ setup.c: int init_db(const char *git_dir, const char *real_git_dir,
     +	 * Now that we have set up both the hash algorithm and the ref storage
     +	 * format we can update the repository's settings accordingly.
     +	 */
    -+	the_repository->hash_algo = &hash_algos[repo_fmt.hash_algo];
    -+	the_repository->ref_storage_format = repo_fmt.ref_storage_format;
    ++	repo_set_hash_algo(the_repository, repo_fmt.hash_algo);
    ++	repo_set_ref_storage_format(the_repository, repo_fmt.ref_storage_format);
     +
      	if (!(flags & INIT_DB_SKIP_REFDB))
      		create_reference_database(repo_fmt.ref_storage_format,
 6:  beeb182f28 =  6:  0a586fa648 setup: introduce "extensions.refStorage" extension
 7:  dd91a75da4 =  7:  6d8754f73a setup: introduce GIT_DEFAULT_REF_FORMAT envvar
 8:  ed3bf008cd =  8:  c645932f3d t: introduce GIT_TEST_DEFAULT_REF_FORMAT envvar
 9:  8a3d950d69 =  9:  761d647770 builtin/rev-parse: introduce `--show-ref-format` flag
10:  4d98b53553 = 10:  e382b5bf08 builtin/init: introduce `--ref-format=` value flag
11:  71cf0ce827 = 11:  257233658d builtin/clone: introduce `--ref-format=` value flag
12:  bbe2fbb154 ! 12:  b8cd06ec53 t9500: write "extensions.refstorage" into config

@@ Commit message
t9500: write "extensions.refstorage" into config

In t9500 we're writing a custom configuration that sets up gitweb. This
- requires us manually ensure that the repository format is configured as
- required, including both the repository format version and extensions.
- With the introduction of the "extensions.refStorage" extension we need
- to update the test to also write this new one.
+ requires us to manually ensure that the repository format is configured
+ as required, including both the repository format version and
+ extensions. With the introduction of the "extensions.refStorage"
+ extension we need to update the test to also write this new one.

base-commit: e79552d19784ee7f4bbce278fe25f93fbda196fa

2.43.GIT

A limited number of tests require repositories to have the default repository format or otherwise they would fail to run, e.g. because they fail to detect the correct hash function. While the hash function is the only extension right now that creates problems like this, we are about to add a second extension for the ref format.

Introduce a new DEFAULT_REPO_FORMAT prereq that can easily be amended whenever we add new format extensions. Next to making any such changes easier on us, the prerequisite's name should also help to clarify the intent better.

---
 t/t3200-branch.sh | 2 +-
 t/test-lib.sh     | 4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

index 6a316f081e..de7d3014e4 100755
@@ -519,7 +519,7 @@ EOF
 
 mv .git/config .git/config-saved
 
-test_expect_success SHA1 'git branch -m q q2 without config should succeed' '
+test_expect_success DEFAULT_REPO_FORMAT 'git branch -m q q2 without config should succeed' '
 	git branch -m q q2 &&
 	git branch -m q2 q
 '

index 876b99562a..dc03f06b8e 100644
@@ -1936,6 +1936,10 @@ test_lazy_prereq SHA1 '
 	esac
 '
 
+test_lazy_prereq DEFAULT_REPO_FORMAT '
+	test_have_prereq SHA1
+'
+
 # Ensure that no test accidentally triggers a Git command
 # that runs the actual maintenance scheduler, affecting a user's
 # system permanently.

2.43.GIT

When calling git init --separate-git-dir=<new-path> on a preexisting repository, we move the Git directory of that repository to the new path specified by the user. If there are worktrees present in the repository, we need to repair the worktrees so that their gitlinks point to the new location of the repository.

This repair logic will load repositories via get_worktrees(), which will enumerate up and initialize all worktrees. Part of initialization is logic that we resolve their respective worktree HEADs, even though that information may not actually be needed in the end by all callers.

In the context of git-init(1) this is about to become a problem, because we do not have a repository that was set up via setup_git_directory() or friends. Consequentially, it is not yet fully initialized at the time of calling repair_worktrees(), and properly setting up all parts of the repository in init_db() before we repair worktrees is not an easy thing to do. While this is okay right now where we only have a single reference backend in Git, once we gain a second one we would be trying to look up the worktree HEADs before we have figured out the reference format, which does not work.

We do not require the worktree HEADs at all to repair worktrees. So let's fix this issue by skipping over the step that reads them.

---
 worktree.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

index a56a6c2a3d..9702ed0308 100644
@@ -51,7 +51,7 @@ static void add_head_info(struct worktree *wt)
 /**
  * get the main worktree
  */
-static struct worktree *get_main_worktree(void)
+static struct worktree *get_main_worktree(int skip_reading_head)
 {
 	struct worktree *worktree = NULL;
 	struct strbuf worktree_path = STRBUF_INIT;

@@ -70,11 +70,13 @@ static struct worktree *get_main_worktree(void)
 	 */
 	worktree->is_bare = (is_bare_repository_cfg == 1) ||
 		is_bare_repository();
-	add_head_info(worktree);
+	if (!skip_reading_head)
+		add_head_info(worktree);
 	return worktree;
 }
 
-static struct worktree *get_linked_worktree(const char *id)
+static struct worktree *get_linked_worktree(const char *id,
+					    int skip_reading_head)
 {
 	struct worktree *worktree = NULL;
 	struct strbuf path = STRBUF_INIT;

@@ -93,7 +95,8 @@ static struct worktree *get_linked_worktree(const char *id)
 	CALLOC_ARRAY(worktree, 1);
 	worktree->path = strbuf_detach(&worktree_path, NULL);
 	worktree->id = xstrdup(id);
-	add_head_info(worktree);
+	if (!skip_reading_head)
+		add_head_info(worktree);
 
 done:
 	strbuf_release(&path);

@@ -118,7 +121,7 @@ static void mark_current_worktree(struct worktree **worktrees)
 	free(git_dir);
 }
 
-struct worktree **get_worktrees(void)
+static struct worktree **get_worktrees_internal(int skip_reading_head)
 {
 	struct worktree **list = NULL;
 	struct strbuf path = STRBUF_INIT;

@@ -128,7 +131,7 @@ struct worktree **get_worktrees(void)
 
 	ALLOC_ARRAY(list, alloc);
 
-	list[counter++] = get_main_worktree();
+	list[counter++] = get_main_worktree(skip_reading_head);
 
 	strbuf_addf(&path, "%s/worktrees", get_git_common_dir());
 	dir = opendir(path.buf);

@@ -137,7 +140,7 @@ struct worktree **get_worktrees(void)
 		while ((d = readdir_skip_dot_and_dotdot(dir)) != NULL) {
 			struct worktree *linked = NULL;
 
-			if ((linked = get_linked_worktree(d->d_name))) {
+			if ((linked = get_linked_worktree(d->d_name, skip_reading_head))) {
 				ALLOC_GROW(list, counter + 1, alloc);
 				list[counter++] = linked;
 			}

@@ -151,6 +154,11 @@ struct worktree **get_worktrees(void)
 	return list;
 }
 
+struct worktree **get_worktrees(void)
+{
+	return get_worktrees_internal(0);
+}
+
 const char *get_worktree_git_dir(const struct worktree *wt)
 {
 	if (!wt)

@@ -591,7 +599,7 @@ static void repair_noop(int iserr UNUSED,
 
 void repair_worktrees(worktree_repair_fn fn, void *cb_data)
 {
-	struct worktree **worktrees = get_worktrees();
+	struct worktree **worktrees = get_worktrees_internal(1);
 	struct worktree **wt = worktrees + 1; /* +1 skips main worktree */
 
 	if (!fn)

2.43.GIT

s/Consequentially/Consequently/

I found it difficult to digest this paragraph with its foreshadowing phrase "about to become a problem" since it wasn't apparent until the very final sentence in the paragraph what the actual problem would be. Perhaps if you mention early on that the reftable backend will have trouble with the current code, it would be easier to grasp. Maybe something like this:

Although not a problem presently with the file-based reference backend, it will become a problem with the upcoming reftable backend. In the context of git-init(1) a fully-materialized repository set up via setup_git_directory() or friends is not yet present. Consequently, it is not yet fully initialized at the time repair_worktrees() is called, and properly setting up all parts of the repository in init_db() before we repair worktrees is not an easy task. With introduction of the reftable backend, it would try to look up the worktree HEADs before we have figured out the reference format, thus would not work.

I forgot to mention that, if you reroll for some reason, the get_worktrees()/get_worktrees_internal() dance might deserve an in-source NEEDSWORK comment explaining that get_worktrees_internal() exists to work around the shortcoming that a corruption-tolerant function for retrieving worktree metadata (for use by the "repair" function) does not yet exist.

Thanks for sharing your thoughts, will do.

Patrick

In order to look up ref storage backends, we're currently using a linked list of backends, where each backend is expected to set up its next pointer to the next ref storage backend. This is kind of a weird setup as backends need to be aware of other backends without much of a reason.

Refactor the code so that the array of backends is centrally defined in "refs.c", where each backend is now identified by an integer constant. Expose functions to translate from those integer constants to the name and vice versa, which will be required by subsequent patches.

---
 refs.c                | 34 +++++++++++++++++++++++++---------
 refs.h                |  3 +++
 refs/debug.c          |  1 -
 refs/files-backend.c  |  1 -
 refs/packed-backend.c |  1 -
 refs/refs-internal.h  |  1 -
 repository.h          |  3 +++
 7 files changed, 31 insertions(+), 13 deletions(-)

index 16bfa21df7..ab14634731 100644
@@ -33,17 +33,33 @@
 /*
  * List of all available backends
  */
-static struct ref_storage_be *refs_backends = &refs_be_files;
+static const struct ref_storage_be *refs_backends[] = {
+	[REF_STORAGE_FORMAT_FILES] = &refs_be_files,
+};
 
-static struct ref_storage_be *find_ref_storage_backend(const char *name)
+static const struct ref_storage_be *find_ref_storage_backend(int ref_storage_format)
 {
-	struct ref_storage_be *be;
-	for (be = refs_backends; be; be = be->next)
-		if (!strcmp(be->name, name))
-			return be;
+	if (ref_storage_format < ARRAY_SIZE(refs_backends))
+		return refs_backends[ref_storage_format];
 	return NULL;
 }
 
+int ref_storage_format_by_name(const char *name)
+{
+	for (int i = 0; i < ARRAY_SIZE(refs_backends); i++)
+		if (refs_backends[i] && !strcmp(refs_backends[i]->name, name))
+			return i;
+	return REF_STORAGE_FORMAT_UNKNOWN;
+}
+
+const char *ref_storage_format_to_name(int ref_storage_format)
+{
+	const struct ref_storage_be *be = find_ref_storage_backend(ref_storage_format);
+	if (!be)
+		return "unknown";
+	return be->name;
+}
+
 /*
  * How to handle various characters in refnames:
  * 0: An acceptable character for refs

@@ -2029,12 +2045,12 @@ static struct ref_store *ref_store_init(struct repository *repo,
 					const char *gitdir,
 					unsigned int flags)
 {
-	const char *be_name = "files";
-	struct ref_storage_be *be = find_ref_storage_backend(be_name);
+	int format = REF_STORAGE_FORMAT_FILES;
+	const struct ref_storage_be *be = find_ref_storage_backend(format);
 	struct ref_store *refs;
 
 	if (!be)
-		BUG("reference backend %s is unknown", be_name);
+		BUG("reference backend is unknown");
 
 	refs = be->init(repo, gitdir, flags);
 	return refs;

index ff113bb12a..e2098ea51b 100644
@@ -11,6 +11,9 @@ struct string_list;
 struct string_list_item;
 struct worktree;
 
+int ref_storage_format_by_name(const char *name);
+const char *ref_storage_format_to_name(int ref_storage_format);
+
 /*
  * Resolve a reference, recursively following symbolic refererences.
  *

index 83b7a0ba65..b9775f2c37 100644
@@ -426,7 +426,6 @@ static int debug_reflog_expire(struct ref_store *ref_store, const char *refname,
 }
 
 struct ref_storage_be refs_be_debug = {
-	.next = NULL,
 	.name = "debug",
 	.init = NULL,
 	.init_db = debug_init_db,

index ad8b1d143f..43fd0ac760 100644
@@ -3241,7 +3241,6 @@ static int files_init_db(struct ref_store *ref_store, struct strbuf *err UNUSED)
 }
 
 struct ref_storage_be refs_be_files = {
-	.next = NULL,
 	.name = "files",
 	.init = files_ref_store_create,
 	.init_db = files_init_db,

index b9fa097a29..8d1090e284 100644
@@ -1705,7 +1705,6 @@ static struct ref_iterator *packed_reflog_iterator_begin(struct ref_store *ref_s
 }
 
 struct ref_storage_be refs_be_packed = {
-	.next = NULL,
 	.name = "packed",
 	.init = packed_ref_store_create,
 	.init_db = packed_init_db,

index 4af83bf9a5..8e9f04cc67 100644
@@ -663,7 +663,6 @@ typedef int read_symbolic_ref_fn(struct ref_store *ref_store, const char *refnam
 				 struct strbuf *referent);
 
 struct ref_storage_be {
-	struct ref_storage_be *next;
 	const char *name;
 	ref_store_init_fn *init;
 	ref_init_db_fn *init_db;

index 5f18486f64..ea4c488b81 100644
@@ -24,6 +24,9 @@ enum fetch_negotiation_setting {
 	FETCH_NEGOTIATION_NOOP,
 };
 
+#define REF_STORAGE_FORMAT_UNKNOWN 0
+#define REF_STORAGE_FORMAT_FILES   1
+
 struct repo_settings {
 	int initialized;
 

2.43.GIT

A small question. Does this have to be "int", or is "unsigned" (or even an enum, rewrittenfrom the "REF_STORAGE_FORMAT_*" family of CPP macro constants) good enough? I am only wondering what happens when you clal find_ref_storage_backend() with a negative index.

For that matter, how REF_STORAGE_FORMAT_UNKNOWN (whose value is 0) is handled by the function also gets curious. The caller may have to find that the backend hasn't been specified by receiving an element in the refs_backends[] array that corresponds to it, but the error behaviour of this function is also to return NULL, so it has to be prepared to handle both cases?

No, it does not have to be an int, and handling a negative index would be a bug. I tried to stick to what we have with GIT_HASH_UNKNOWN, GIT_HASH_SHA1 etc, which is exactly similar in spirit. Whether it's the perfect way to handle this... probably not. Without the context I would've used an enum, but instead I opted for consistency.

Yeah, we do not really discern those two cases for now and instead just return NULL both for any unknown ref storage format. All callers know to handle NULL, but the error handling will only report a generic "unknown" backend error.

The easiest way to discern those cases would be to BUG() when being passed an invalid ref storage format smaller than 0 or larger than the number of known backends. Because ultimately it is just that, a bug that shouldn't ever occur.

Not sure whether this is worth a reroll?

Patrick

By using an unsigned type, you no longer have to worry about getting handed a negative index, as the "must be smaller than ARRAY_SIZE()" check will be sufficient to catch anybody who passes "-1" (casted to unsigned by parameter passing). So I would say that would be a good enough reason to reroll, whether we differentiate 0 and an index that is larger than refs_backends[] (or a negative one) with an explicit BUG(), or just leave it to the caller by returning NULL. As to the error handling, I suspect it is sufficient to return NULL and let the caller handle it.

Thanks.

In order to discern which ref storage format a repository is supposed to use we need to start setting up and/or discovering the format. This needs to happen in two separate code paths.

- The first path is when we create a repository via init_db(). When we are re-initializing a preexisting repository we need to retain the previously used ref storage format -- if the user asked for a different format then this indicates an error and we error out. Otherwise we either initialize the repository with the format asked for by the user or the default format, which currently is the "files" backend.

- The second path is when discovering repositories, where we need to read the config of that repository. There is not yet any way to configure something other than the "files" backend, so we can just blindly set the ref storage format to this backend.

Wire up this logic so that we have the ref storage format always readily available when needed. As there is only a single backend and because it is not configurable we cannot yet verify that this tracking works as expected via tests, but tests will be added in subsequent commits. To countermand this ommission now though, raise a BUG() in case the ref storage format is not set up properly in ref_store_init().

---
 builtin/clone.c   |  5 +++--
 builtin/init-db.c |  4 +++-
 refs.c            |  4 ++--
 repository.c      |  6 ++++++
 repository.h      |  4 ++++
 setup.c           | 26 +++++++++++++++++++++++---
 setup.h           |  6 +++++-
 7 files changed, 46 insertions(+), 9 deletions(-)

index 343f536cf8..48aeb1b90b 100644
@@ -1107,7 +1107,8 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	 * repository, and reference backends may persist that information into
 	 * their on-disk data structures.
 	 */
-	init_db(git_dir, real_git_dir, option_template, GIT_HASH_UNKNOWN, NULL,
+	init_db(git_dir, real_git_dir, option_template, GIT_HASH_UNKNOWN,
+		REF_STORAGE_FORMAT_UNKNOWN, NULL,
 		do_not_override_repo_unix_permissions, INIT_DB_QUIET | INIT_DB_SKIP_REFDB);
 
 	if (real_git_dir) {

@@ -1292,7 +1293,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	hash_algo = hash_algo_by_ptr(transport_get_hash_algo(transport));
 	initialize_repository_version(hash_algo, 1);
 	repo_set_hash_algo(the_repository, hash_algo);
-	create_reference_database(NULL, 1);
+	create_reference_database(the_repository->ref_storage_format, NULL, 1);
 
 	/*
 	 * Before fetching from the remote, download and install bundle

index cb727c826f..b6e80feab6 100644
@@ -11,6 +11,7 @@
 #include "object-file.h"
 #include "parse-options.h"
 #include "path.h"
+#include "refs.h"
 #include "setup.h"
 #include "strbuf.h"
 

@@ -236,5 +237,6 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 
 	flags |= INIT_DB_EXIST_OK;
 	return init_db(git_dir, real_git_dir, template_dir, hash_algo,
-		       initial_branch, init_shared_repository, flags);
+		       REF_STORAGE_FORMAT_UNKNOWN, initial_branch,
+		       init_shared_repository, flags);
 }

index ab14634731..be8fcabde0 100644
@@ -2045,10 +2045,10 @@ static struct ref_store *ref_store_init(struct repository *repo,
 					const char *gitdir,
 					unsigned int flags)
 {
-	int format = REF_STORAGE_FORMAT_FILES;
-	const struct ref_storage_be *be = find_ref_storage_backend(format);
+	const struct ref_storage_be *be;
 	struct ref_store *refs;
 
+	be = find_ref_storage_backend(repo->ref_storage_format);
 	if (!be)
 		BUG("reference backend is unknown");
 

index a7679ceeaa..691cabf45b 100644
@@ -104,6 +104,11 @@ void repo_set_hash_algo(struct repository *repo, int hash_algo)
 	repo->hash_algo = &hash_algos[hash_algo];
 }
 
+void repo_set_ref_storage_format(struct repository *repo, int format)
+{
+	repo->ref_storage_format = format;
+}
+
 /*
  * Attempt to resolve and set the provided 'gitdir' for repository 'repo'.
  * Return 0 upon success and a non-zero value upon failure.

@@ -184,6 +189,7 @@ int repo_init(struct repository *repo,
 		goto error;
 
 	repo_set_hash_algo(repo, format.hash_algo);
+	repo_set_ref_storage_format(repo, format.ref_storage_format);
 	repo->repository_format_worktree_config = format.worktree_config;
 
 	/* take ownership of format.partial_clone */

index ea4c488b81..d3a24da4d6 100644
@@ -163,6 +163,9 @@ struct repository {
 	/* Repository's current hash algorithm, as serialized on disk. */
 	const struct git_hash_algo *hash_algo;
 
+	/* Repository's reference storage format, as serialized on disk. */
+	int ref_storage_format;
+
 	/* A unique-id for tracing purposes. */
 	int trace2_repo_id;
 

@@ -202,6 +205,7 @@ void repo_set_gitdir(struct repository *repo, const char *root,
 		     const struct set_gitdir_args *extra_args);
 void repo_set_worktree(struct repository *repo, const char *path);
 void repo_set_hash_algo(struct repository *repo, int algo);
+void repo_set_ref_storage_format(struct repository *repo, int format);
 void initialize_the_repository(void);
 RESULT_MUST_BE_USED
 int repo_init(struct repository *r, const char *gitdir, const char *worktree);

index bc90bbd033..e58ab7e786 100644
@@ -1566,6 +1566,8 @@ const char *setup_git_directory_gently(int *nongit_ok)
 		}
 		if (startup_info->have_repository) {
 			repo_set_hash_algo(the_repository, repo_fmt.hash_algo);
+			repo_set_ref_storage_format(the_repository,
+						    repo_fmt.ref_storage_format);
 			the_repository->repository_format_worktree_config =
 				repo_fmt.worktree_config;
 			/* take ownership of repo_fmt.partial_clone */

@@ -1659,6 +1661,8 @@ void check_repository_format(struct repository_format *fmt)
 	check_repository_format_gently(get_git_dir(), fmt, NULL);
 	startup_info->have_repository = 1;
 	repo_set_hash_algo(the_repository, fmt->hash_algo);
+	repo_set_ref_storage_format(the_repository,
+				    fmt->ref_storage_format);
 	the_repository->repository_format_worktree_config =
 		fmt->worktree_config;
 	the_repository->repository_format_partial_clone =

@@ -1899,7 +1903,8 @@ static int is_reinit(void)
 	return ret;
 }
 
-void create_reference_database(const char *initial_branch, int quiet)
+void create_reference_database(int ref_storage_format,
+			       const char *initial_branch, int quiet)
 {
 	struct strbuf err = STRBUF_INIT;
 	int reinit = is_reinit();

@@ -1919,6 +1924,7 @@ void create_reference_database(const char *initial_branch, int quiet)
 	safe_create_dir(git_path("refs"), 1);
 	adjust_shared_perm(git_path("refs"));
 
+	repo_set_ref_storage_format(the_repository, ref_storage_format);
 	if (refs_init_db(&err))
 		die("failed to set up refs db: %s", err.buf);
 

@@ -2137,8 +2143,20 @@ static void validate_hash_algorithm(struct repository_format *repo_fmt, int hash
 	}
 }
 
+static void validate_ref_storage_format(struct repository_format *repo_fmt, int format)
+{
+	if (repo_fmt->version >= 0 &&
+	    format != REF_STORAGE_FORMAT_UNKNOWN &&
+	    format != repo_fmt->ref_storage_format) {
+		die(_("attempt to reinitialize repository with different reference storage format"));
+	} else if (format != REF_STORAGE_FORMAT_UNKNOWN) {
+		repo_fmt->ref_storage_format = format;
+	}
+}
+
 int init_db(const char *git_dir, const char *real_git_dir,
-	    const char *template_dir, int hash, const char *initial_branch,
+	    const char *template_dir, int hash,
+	    int ref_storage_format, const char *initial_branch,
 	    int init_shared_repository, unsigned int flags)
 {
 	int reinit;

@@ -2181,13 +2199,15 @@ int init_db(const char *git_dir, const char *real_git_dir,
 	check_repository_format(&repo_fmt);
 
 	validate_hash_algorithm(&repo_fmt, hash);
+	validate_ref_storage_format(&repo_fmt, ref_storage_format);
 
 	reinit = create_default_files(template_dir, original_git_dir,
 				      &repo_fmt, prev_bare_repository,
 				      init_shared_repository);
 
 	if (!(flags & INIT_DB_SKIP_REFDB))
-		create_reference_database(initial_branch, flags & INIT_DB_QUIET);
+		create_reference_database(repo_fmt.ref_storage_format,
+					  initial_branch, flags & INIT_DB_QUIET);
 	create_object_directory();
 
 	if (get_shared_repository()) {

index 3f0f17c351..4927abf2cf 100644
@@ -115,6 +115,7 @@ struct repository_format {
 	int worktree_config;
 	int is_bare;
 	int hash_algo;
+	int ref_storage_format;
 	int sparse_index;
 	char *work_tree;
 	struct string_list unknown_extensions;

@@ -131,6 +132,7 @@ struct repository_format {
 	.version = -1, \
 	.is_bare = -1, \
 	.hash_algo = GIT_HASH_SHA1, \
+	.ref_storage_format = REF_STORAGE_FORMAT_FILES, \
 	.unknown_extensions = STRING_LIST_INIT_DUP, \
 	.v1_only_extensions = STRING_LIST_INIT_DUP, \
 }

@@ -175,10 +177,12 @@ void check_repository_format(struct repository_format *fmt);
 
 int init_db(const char *git_dir, const char *real_git_dir,
 	    const char *template_dir, int hash_algo,
+	    int ref_storage_format,
 	    const char *initial_branch, int init_shared_repository,
 	    unsigned int flags);
 void initialize_repository_version(int hash_algo, int reinit);
-void create_reference_database(const char *initial_branch, int quiet);
+void create_reference_database(int ref_storage_format,
+			       const char *initial_branch, int quiet);
 
 /*
  * NOTE NOTE NOTE!!

2.43.GIT

The proper hash algorithm and ref storage format that will be used for a newly initialized repository will be figured out in init_db() via validate_hash_algorithm() and validate_ref_storage_format(). Until now though, we never set up the hash algorithm or ref storage format of the_repository accordingly.

There are only two callsites of init_db(), one in git-init(1) and one in git-clone(1). The former function doesn't care for the formats to be set up properly because it never access the repository after calling the function in the first place.

For git-clone(1) it's a different story though, as we call init_db() before listing remote refs. While we do indeed have the wrong hash function in the_repository when init_db() sets up a non-default object format for the repository, it never mattered because we adjust the hash after learning about the remote's hash function via the listed refs.

So the current state is correct for the hash algo, but it's not for the ref storage format because git-clone(1) wouldn't know to set it up properly. But instead of adjusting only the ref_storage_format, set both the hash algo and the ref storage format so that the_repository is in the correct state when init_db() exits. This is fine as we will adjust the hash later on anyway and makes it easier to reason about the end state of the_repository.

---
 setup.c | 7 +++++++
 1 file changed, 7 insertions(+)

index e58ab7e786..3d980814bc 100644
@@ -2205,6 +2205,13 @@ int init_db(const char *git_dir, const char *real_git_dir,
 				      &repo_fmt, prev_bare_repository,
 				      init_shared_repository);
 
+	/*
+	 * Now that we have set up both the hash algorithm and the ref storage
+	 * format we can update the repository's settings accordingly.
+	 */
+	repo_set_hash_algo(the_repository, repo_fmt.hash_algo);
+	repo_set_ref_storage_format(the_repository, repo_fmt.ref_storage_format);
+
 	if (!(flags & INIT_DB_SKIP_REFDB))
 		create_reference_database(repo_fmt.ref_storage_format,
 					  initial_branch, flags & INIT_DB_QUIET);

2.43.GIT

Introduce a new "extensions.refStorage" extension that allows us to specify the ref storage format used by a repository. For now, the only supported format is the "files" format, but this list will likely soon be extended to also support the upcoming "reftable" format.

There have been discussions on the Git mailing list in the past around how exactly this extension should look like. One alternative [1] that was discussed was whether it would make sense to model the extension in such a way that backends are arbitrarily stackable. This would allow for a combined value of e.g. "loose,packed-refs" or "loose,reftable", which indicates that new refs would be written via "loose" files backend and compressed into "packed-refs" or "reftable" backends, respectively.

It is arguable though whether this flexibility and the complexity that it brings with it is really required for now. It is not foreseeable that there will be a proliferation of backends in the near-term future, and the current set of existing formats and formats which are on the horizon can easily be configured with the much simpler proposal where we have a single value, only.

Furthermore, if we ever see that we indeed want to gain the ability to arbitrarily stack the ref formats, then we can adapt the current extension rather easily. Given that Git clients will refuse any unknown value for the "extensions.refStorage" extension they would also know to ignore a stacked "loose,packed-refs" in the future.

So let's stick with the easy proposal for the time being and wire up the extension.

[1]: <[email protected]>

---
 Documentation/config/extensions.txt           | 11 ++++++++
 Documentation/ref-storage-format.txt          |  1 +
 .../technical/repository-version.txt          |  5 ++++
 builtin/clone.c                               |  2 +-
 setup.c                                       | 23 +++++++++++++---
 setup.h                                       |  3 ++-
 t/t0001-init.sh                               | 26 +++++++++++++++++++
 t/test-lib.sh                                 |  2 +-
 8 files changed, 67 insertions(+), 6 deletions(-)
 create mode 100644 Documentation/ref-storage-format.txt

index bccaec7a96..66db0e15da 100644
@@ -7,6 +7,17 @@ Note that this setting should only be set by linkgit:git-init[1] or
 linkgit:git-clone[1].  Trying to change it after initialization will not
 work and will produce hard-to-diagnose issues.
 
+extensions.refStorage::
+	Specify the ref storage format to use. The acceptable values are:
++
+include::../ref-storage-format.txt[]
++
+It is an error to specify this key unless `core.repositoryFormatVersion` is 1.
++
+Note that this setting should only be set by linkgit:git-init[1] or
+linkgit:git-clone[1]. Trying to change it after initialization will not
+work and will produce hard-to-diagnose issues.
+
 extensions.worktreeConfig::
 	If enabled, then worktrees will load config settings from the
 	`$GIT_DIR/config.worktree` file in addition to the

new file mode 100644
index 0000000000..1a65cac468
@@ -0,0 +1 @@
+* `files` for loose files with packed-refs. This is the default.

index 045a76756f..27be3741e6 100644
@@ -100,3 +100,8 @@ If set, by default "git config" reads from both "config" and
 multiple working directory mode, "config" file is shared while
 "config.worktree" is per-working directory (i.e., it's in
 GIT_COMMON_DIR/worktrees/<id>/config.worktree)
+
+==== `refStorage`
+
+Specifies the file format for the ref database. The only valid value
+is `files` (loose references with a packed-refs file).

index 48aeb1b90b..0fb3816d0c 100644
@@ -1291,7 +1291,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	 * ours to the same thing.
 	 */
 	hash_algo = hash_algo_by_ptr(transport_get_hash_algo(transport));
-	initialize_repository_version(hash_algo, 1);
+	initialize_repository_version(hash_algo, the_repository->ref_storage_format, 1);
 	repo_set_hash_algo(the_repository, hash_algo);
 	create_reference_database(the_repository->ref_storage_format, NULL, 1);
 

index 3d980814bc..3aac8c01cd 100644
@@ -592,6 +592,17 @@ static enum extension_result handle_extension(const char *var,
 				     "extensions.objectformat", value);
 		data->hash_algo = format;
 		return EXTENSION_OK;
+	} else if (!strcmp(ext, "refstorage")) {
+		int format;
+
+		if (!value)
+			return config_error_nonbool(var);
+		format = ref_storage_format_by_name(value);
+		if (format == REF_STORAGE_FORMAT_UNKNOWN)
+			return error(_("invalid value for '%s': '%s'"),
+				     "extensions.refstorage", value);
+		data->ref_storage_format = format;
+		return EXTENSION_OK;
 	}
 	return EXTENSION_UNKNOWN;
 }

@@ -1871,12 +1882,14 @@ static int needs_work_tree_config(const char *git_dir, const char *work_tree)
 	return 1;
 }
 
-void initialize_repository_version(int hash_algo, int reinit)
+void initialize_repository_version(int hash_algo, int ref_storage_format,
+				   int reinit)
 {
 	char repo_version_string[10];
 	int repo_version = GIT_REPO_VERSION;
 
-	if (hash_algo != GIT_HASH_SHA1)
+	if (hash_algo != GIT_HASH_SHA1 ||
+	    ref_storage_format != REF_STORAGE_FORMAT_FILES)
 		repo_version = GIT_REPO_VERSION_READ;
 
 	/* This forces creation of new config file */

@@ -1889,6 +1902,10 @@ void initialize_repository_version(int hash_algo, int reinit)
 			       hash_algos[hash_algo].name);
 	else if (reinit)
 		git_config_set_gently("extensions.objectformat", NULL);
+
+	if (ref_storage_format != REF_STORAGE_FORMAT_FILES)
+		git_config_set("extensions.refstorage",
+			       ref_storage_format_to_name(ref_storage_format));
 }
 
 static int is_reinit(void)

@@ -2030,7 +2047,7 @@ static int create_default_files(const char *template_path,
 		adjust_shared_perm(get_git_dir());
 	}
 
-	initialize_repository_version(fmt->hash_algo, 0);
+	initialize_repository_version(fmt->hash_algo, fmt->ref_storage_format, 0);
 
 	/* Check filemode trustability */
 	path = git_path_buf(&buf, "config");

index 4927abf2cf..89033ae1d9 100644
@@ -180,7 +180,8 @@ int init_db(const char *git_dir, const char *real_git_dir,
 	    int ref_storage_format,
 	    const char *initial_branch, int init_shared_repository,
 	    unsigned int flags);
-void initialize_repository_version(int hash_algo, int reinit);
+void initialize_repository_version(int hash_algo, int ref_storage_format,
+				   int reinit);
 void create_reference_database(int ref_storage_format,
 			       const char *initial_branch, int quiet);
 

index 2b78e3be47..38b3e4c39e 100755
@@ -532,6 +532,32 @@ test_expect_success 'init rejects attempts to initialize with different hash' '
 	test_must_fail git -C sha256 init --object-format=sha1
 '
 
+test_expect_success DEFAULT_REPO_FORMAT 'extensions.refStorage is not allowed with repo version 0' '
+	test_when_finished "rm -rf refstorage" &&
+	git init refstorage &&
+	git -C refstorage config extensions.refStorage files &&
+	test_must_fail git -C refstorage rev-parse 2>err &&
+	grep "repo version is 0, but v1-only extension found" err
+'
+
+test_expect_success DEFAULT_REPO_FORMAT 'extensions.refStorage with files backend' '
+	test_when_finished "rm -rf refstorage" &&
+	git init refstorage &&
+	git -C refstorage config core.repositoryformatversion 1 &&
+	git -C refstorage config extensions.refStorage files &&
+	test_commit -C refstorage A &&
+	git -C refstorage rev-parse --verify HEAD
+'
+
+test_expect_success DEFAULT_REPO_FORMAT 'extensions.refStorage with unknown backend' '
+	test_when_finished "rm -rf refstorage" &&
+	git init refstorage &&
+	git -C refstorage config core.repositoryformatversion 1 &&
+	git -C refstorage config extensions.refStorage garbage &&
+	test_must_fail git -C refstorage rev-parse 2>err &&
+	grep "invalid value for ${SQ}extensions.refstorage${SQ}: ${SQ}garbage${SQ}" err
+'
+
 test_expect_success MINGW 'core.hidedotfiles = false' '
 	git config --global core.hidedotfiles false &&
 	rm -rf newdir &&

index dc03f06b8e..4685cc3d48 100644
@@ -1937,7 +1937,7 @@ test_lazy_prereq SHA1 '
 '
 
 test_lazy_prereq DEFAULT_REPO_FORMAT '
-	test_have_prereq SHA1
+	test_have_prereq SHA1,REFFILES
 '
 
 # Ensure that no test accidentally triggers a Git command

2.43.GIT

Introduce a new GIT_DEFAULT_REF_FORMAT environment variable that lets users control the default ref format used by both git-init(1) and git-clone(1). This is modeled after GIT_DEFAULT_OBJECT_FORMAT, which does the same thing for the repository's object format.

---
 Documentation/git.txt |  5 +++++
 setup.c               |  7 +++++++
 t/t0001-init.sh       | 18 ++++++++++++++++++
 3 files changed, 30 insertions(+)

index bf9e6af695..88e4ed4bd6 100644
@@ -556,6 +556,11 @@ double-quotes and respecting backslash escapes. E.g., the value
 	is always used. The default is "sha1".
 	See `--object-format` in linkgit:git-init[1].
 
+`GIT_DEFAULT_REF_FORMAT`::
+	If this variable is set, the default reference backend format for new
+	repositories will be set to this value. The default is "files".
+	See `--ref-format` in linkgit:git-init[1].
+
 Git Commits
 ~~~~~~~~~~~
 `GIT_AUTHOR_NAME`::

index 3aac8c01cd..4712bba6f8 100644
@@ -2162,12 +2162,19 @@ static void validate_hash_algorithm(struct repository_format *repo_fmt, int hash
 
 static void validate_ref_storage_format(struct repository_format *repo_fmt, int format)
 {
+	const char *name = getenv("GIT_DEFAULT_REF_FORMAT");
+
 	if (repo_fmt->version >= 0 &&
 	    format != REF_STORAGE_FORMAT_UNKNOWN &&
 	    format != repo_fmt->ref_storage_format) {
 		die(_("attempt to reinitialize repository with different reference storage format"));
 	} else if (format != REF_STORAGE_FORMAT_UNKNOWN) {
 		repo_fmt->ref_storage_format = format;
+	} else if (name) {
+		format = ref_storage_format_by_name(name);
+		if (format == REF_STORAGE_FORMAT_UNKNOWN)
+			die(_("unknown ref storage format '%s'"), name);
+		repo_fmt->ref_storage_format = format;
 	}
 }
 

index 38b3e4c39e..30ce752cc1 100755
@@ -558,6 +558,24 @@ test_expect_success DEFAULT_REPO_FORMAT 'extensions.refStorage with unknown back
 	grep "invalid value for ${SQ}extensions.refstorage${SQ}: ${SQ}garbage${SQ}" err
 '
 
+test_expect_success DEFAULT_REPO_FORMAT 'init with GIT_DEFAULT_REF_FORMAT=files' '
+	test_when_finished "rm -rf refformat" &&
+	GIT_DEFAULT_REF_FORMAT=files git init refformat &&
+	echo 0 >expect &&
+	git -C refformat config core.repositoryformatversion >actual &&
+	test_cmp expect actual &&
+	test_must_fail git -C refformat config extensions.refstorage
+'
+
+test_expect_success 'init with GIT_DEFAULT_REF_FORMAT=garbage' '
+	test_when_finished "rm -rf refformat" &&
+	cat >expect <<-EOF &&
+	fatal: unknown ref storage format ${SQ}garbage${SQ}
+	EOF
+	test_must_fail env GIT_DEFAULT_REF_FORMAT=garbage git init refformat 2>err &&
+	test_cmp expect err
+'
+
 test_expect_success MINGW 'core.hidedotfiles = false' '
 	git config --global core.hidedotfiles false &&
 	rm -rf newdir &&

2.43.GIT

Introduce a new GIT_TEST_DEFAULT_REF_FORMAT environment variable that lets developers run the test suite with a different default ref format without impacting the ref format used by non-test Git invocations. This is modeled after GIT_TEST_DEFAULT_OBJECT_FORMAT, which does the same thing for the repository's object format.

Adapt the setup of the REFFILES test prerequisite to be conditionally set based on the default ref format.

---
 t/README                |  3 +++
 t/test-lib-functions.sh |  5 +++++
 t/test-lib.sh           | 11 ++++++++++-
 3 files changed, 18 insertions(+), 1 deletion(-)

index 36463d0742..621d3b8c09 100644
@@ -479,6 +479,9 @@ GIT_TEST_DEFAULT_HASH=<hash-algo> specifies which hash algorithm to
 use in the test scripts. Recognized values for <hash-algo> are "sha1"
 and "sha256".
 
+GIT_TEST_DEFAULT_REF_FORMAT=<format> specifies which ref storage format
+to use in the test scripts. Recognized values for <format> are "files".
+
 GIT_TEST_NO_WRITE_REV_INDEX=<boolean>, when true disables the
 'pack.writeReverseIndex' setting.
 

index 5eb57914ab..a3a51ea9e8 100644
@@ -1659,6 +1659,11 @@ test_detect_hash () {
 	test_hash_algo="${GIT_TEST_DEFAULT_HASH:-sha1}"
 }
 
+# Detect the hash algorithm in use.
+test_detect_ref_format () {
+	echo "${GIT_TEST_DEFAULT_REF_FORMAT:-files}"
+}
+
 # Load common hash metadata and common placeholder object IDs for use with
 # test_oid.
 test_oid_init () {

index 4685cc3d48..fc93aa57e6 100644
@@ -542,6 +542,8 @@ export EDITOR
 
 GIT_DEFAULT_HASH="${GIT_TEST_DEFAULT_HASH:-sha1}"
 export GIT_DEFAULT_HASH
+GIT_DEFAULT_REF_FORMAT="${GIT_TEST_DEFAULT_REF_FORMAT:-files}"
+export GIT_DEFAULT_REF_FORMAT
 GIT_TEST_MERGE_ALGORITHM="${GIT_TEST_MERGE_ALGORITHM:-ort}"
 export GIT_TEST_MERGE_ALGORITHM
 

@@ -1745,7 +1747,14 @@ parisc* | hppa*)
 	;;
 esac
 
-test_set_prereq REFFILES
+case "$GIT_DEFAULT_REF_FORMAT" in
+files)
+	test_set_prereq REFFILES;;
+*)
+	echo 2>&1 "error: unknown ref format $GIT_DEFAULT_REF_FORMAT"
+	exit 1
+	;;
+esac
 
 ( COLUMNS=1 && test $COLUMNS = 1 ) && test_set_prereq COLUMNS_CAN_BE_1
 test -z "$NO_CURL" && test_set_prereq LIBCURL

2.43.GIT

Introduce a new --show-ref-format to git-rev-parse(1) that causes it to print the ref format used by a repository.

---
 Documentation/git-rev-parse.txt |  3 +++
 builtin/rev-parse.c             |  4 ++++
 t/t1500-rev-parse.sh            | 17 +++++++++++++++++
 3 files changed, 24 insertions(+)

index 912fab9f5e..546faf9017 100644
@@ -307,6 +307,9 @@ The following options are unaffected by `--path-format`:
 	input, multiple algorithms may be printed, space-separated.
 	If not specified, the default is "storage".
 
+--show-ref-format::
+	Show the reference storage format used for the repository.
+
 
 Other Options
 ~~~~~~~~~~~~~

index 917f122440..d08987646a 100644
@@ -1062,6 +1062,10 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 				puts(the_hash_algo->name);
 				continue;
 			}
+			if (!strcmp(arg, "--show-ref-format")) {
+				puts(ref_storage_format_to_name(the_repository->ref_storage_format));
+				continue;
+			}
 			if (!strcmp(arg, "--end-of-options")) {
 				seen_end_of_options = 1;
 				if (filter & (DO_FLAGS | DO_REVS))

index 3f9e7f62e4..a669e592f1 100755
@@ -208,6 +208,23 @@ test_expect_success 'rev-parse --show-object-format in repo' '
 	grep "unknown mode for --show-object-format: squeamish-ossifrage" err
 '
 
+test_expect_success 'rev-parse --show-ref-format' '
+	test_detect_ref_format >expect &&
+	git rev-parse --show-ref-format >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rev-parse --show-ref-format with invalid storage' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		git config extensions.refstorage broken &&
+		test_must_fail git rev-parse --show-ref-format 2>err &&
+		grep "error: invalid value for ${SQ}extensions.refstorage${SQ}: ${SQ}broken${SQ}" err
+	)
+'
+
 test_expect_success '--show-toplevel from subdir of working tree' '
 	pwd >expect &&
 	git -C sub/dir rev-parse --show-toplevel >actual &&

2.43.GIT

Introduce a new --ref-format value flag for git-init(1) that allows the user to specify the ref format that is to be used for a newly initialized repository.

---
 Documentation/git-init.txt |  7 +++++++
 builtin/init-db.c          | 13 ++++++++++++-
 t/t0001-init.sh            | 26 ++++++++++++++++++++++++++
 3 files changed, 45 insertions(+), 1 deletion(-)

index 6f0d2973bf..e8dc645bb5 100644
@@ -11,6 +11,7 @@ SYNOPSIS
 [verse]
 'git init' [-q | --quiet] [--bare] [--template=<template-directory>]
 	  [--separate-git-dir <git-dir>] [--object-format=<format>]
+	  [--ref-format=<format>]
 	  [-b <branch-name> | --initial-branch=<branch-name>]
 	  [--shared[=<permissions>]] [<directory>]
 

@@ -57,6 +58,12 @@ values are 'sha1' and (if enabled) 'sha256'.  'sha1' is the default.
 +
 include::object-format-disclaimer.txt[]
 
+--ref-format=<format>::
+
+Specify the given ref storage format for the repository. The valid values are:
++
+include::ref-storage-format.txt[]
+
 --template=<template-directory>::
 
 Specify the directory from which templates will be used.  (See the "TEMPLATE

index b6e80feab6..770b2822fe 100644
@@ -58,6 +58,7 @@ static int shared_callback(const struct option *opt, const char *arg, int unset)
 static const char *const init_db_usage[] = {
 	N_("git init [-q | --quiet] [--bare] [--template=<template-directory>]\n"
 	   "         [--separate-git-dir <git-dir>] [--object-format=<format>]\n"
+	   "         [--ref-format=<format>]\n"
 	   "         [-b <branch-name> | --initial-branch=<branch-name>]\n"
 	   "         [--shared[=<permissions>]] [<directory>]"),
 	NULL

@@ -77,8 +78,10 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 	const char *template_dir = NULL;
 	unsigned int flags = 0;
 	const char *object_format = NULL;
+	const char *ref_format = NULL;
 	const char *initial_branch = NULL;
 	int hash_algo = GIT_HASH_UNKNOWN;
+	int ref_storage_format = REF_STORAGE_FORMAT_UNKNOWN;
 	int init_shared_repository = -1;
 	const struct option init_db_options[] = {
 		OPT_STRING(0, "template", &template_dir, N_("template-directory"),

@@ -96,6 +99,8 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 			   N_("override the name of the initial branch")),
 		OPT_STRING(0, "object-format", &object_format, N_("hash"),
 			   N_("specify the hash algorithm to use")),
+		OPT_STRING(0, "ref-format", &ref_format, N_("format"),
+			   N_("specify the reference format to use")),
 		OPT_END()
 	};
 

@@ -159,6 +164,12 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 			die(_("unknown hash algorithm '%s'"), object_format);
 	}
 
+	if (ref_format) {
+		ref_storage_format = ref_storage_format_by_name(ref_format);
+		if (ref_storage_format == REF_STORAGE_FORMAT_UNKNOWN)
+			die(_("unknown ref storage format '%s'"), ref_format);
+	}
+
 	if (init_shared_repository != -1)
 		set_shared_repository(init_shared_repository);
 

@@ -237,6 +248,6 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 
 	flags |= INIT_DB_EXIST_OK;
 	return init_db(git_dir, real_git_dir, template_dir, hash_algo,
-		       REF_STORAGE_FORMAT_UNKNOWN, initial_branch,
+		       ref_storage_format, initial_branch,
 		       init_shared_repository, flags);
 }

index 30ce752cc1..b131d665db 100755
@@ -576,6 +576,32 @@ test_expect_success 'init with GIT_DEFAULT_REF_FORMAT=garbage' '
 	test_cmp expect err
 '
 
+test_expect_success 'init with --ref-format=files' '
+	test_when_finished "rm -rf refformat" &&
+	git init --ref-format=files refformat &&
+	echo files >expect &&
+	git -C refformat rev-parse --show-ref-format >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 're-init with same format' '
+	test_when_finished "rm -rf refformat" &&
+	git init --ref-format=files refformat &&
+	git init --ref-format=files refformat &&
+	echo files >expect &&
+	git -C refformat rev-parse --show-ref-format >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'init with --ref-format=garbage' '
+	test_when_finished "rm -rf refformat" &&
+	cat >expect <<-EOF &&
+	fatal: unknown ref storage format ${SQ}garbage${SQ}
+	EOF
+	test_must_fail git init --ref-format=garbage refformat 2>err &&
+	test_cmp expect err
+'
+
 test_expect_success MINGW 'core.hidedotfiles = false' '
 	git config --global core.hidedotfiles false &&
 	rm -rf newdir &&

2.43.GIT

Introduce a new --ref-format value flag for git-clone(1) that allows the user to specify the ref format that is to be used for a newly initialized repository.

---
 Documentation/git-clone.txt |  6 ++++++
 builtin/clone.c             | 12 +++++++++++-
 t/t5601-clone.sh            | 17 +++++++++++++++++
 3 files changed, 34 insertions(+), 1 deletion(-)

index c37c4a37f7..6e43eb9c20 100644
@@ -311,6 +311,12 @@ or `--mirror` is given)
 	The result is Git repository can be separated from working
 	tree.
 
+--ref-format=<ref-format::
+
+Specify the given ref storage format for the repository. The valid values are:
++
+include::ref-storage-format.txt[]
+
 -j <n>::
 --jobs <n>::
 	The number of submodules fetched at the same time.

index 0fb3816d0c..18093d5d16 100644
@@ -72,6 +72,7 @@ static char *remote_name = NULL;
 static char *option_branch = NULL;
 static struct string_list option_not = STRING_LIST_INIT_NODUP;
 static const char *real_git_dir;
+static const char *ref_format;
 static char *option_upload_pack = "git-upload-pack";
 static int option_verbosity;
 static int option_progress = -1;

@@ -157,6 +158,8 @@ static struct option builtin_clone_options[] = {
 		    N_("any cloned submodules will be shallow")),
 	OPT_STRING(0, "separate-git-dir", &real_git_dir, N_("gitdir"),
 		   N_("separate git dir from working tree")),
+	OPT_STRING(0, "ref-format", &ref_format, N_("format"),
+		   N_("specify the reference format to use")),
 	OPT_STRING_LIST('c', "config", &option_config, N_("key=value"),
 			N_("set config inside the new repository")),
 	OPT_STRING_LIST(0, "server-option", &server_options,

@@ -932,6 +935,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	int submodule_progress;
 	int filter_submodules = 0;
 	int hash_algo;
+	int ref_storage_format = REF_STORAGE_FORMAT_UNKNOWN;
 	const int do_not_override_repo_unix_permissions = -1;
 
 	struct transport_ls_refs_options transport_ls_refs_options =

@@ -957,6 +961,12 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	if (option_single_branch == -1)
 		option_single_branch = deepen ? 1 : 0;
 
+	if (ref_format) {
+		ref_storage_format = ref_storage_format_by_name(ref_format);
+		if (ref_storage_format == REF_STORAGE_FORMAT_UNKNOWN)
+			die(_("unknown ref storage format '%s'"), ref_format);
+	}
+
 	if (option_mirror)
 		option_bare = 1;
 

@@ -1108,7 +1118,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	 * their on-disk data structures.
 	 */
 	init_db(git_dir, real_git_dir, option_template, GIT_HASH_UNKNOWN,
-		REF_STORAGE_FORMAT_UNKNOWN, NULL,
+		ref_storage_format, NULL,
 		do_not_override_repo_unix_permissions, INIT_DB_QUIET | INIT_DB_SKIP_REFDB);
 
 	if (real_git_dir) {

index 47eae641f0..fb1b9c686d 100755
@@ -157,6 +157,23 @@ test_expect_success 'clone --mirror does not repeat tags' '
 
 '
 
+test_expect_success 'clone with files ref format' '
+	test_when_finished "rm -rf ref-storage" &&
+	git clone --ref-format=files --mirror src ref-storage &&
+	echo files >expect &&
+	git -C ref-storage rev-parse --show-ref-format >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'clone with garbage ref format' '
+	cat >expect <<-EOF &&
+	fatal: unknown ref storage format ${SQ}garbage${SQ}
+	EOF
+	test_must_fail git clone --ref-format=garbage --mirror src ref-storage 2>err &&
+	test_cmp expect err &&
+	test_path_is_missing ref-storage
+'
+
 test_expect_success 'clone to destination with trailing /' '
 
 	git clone src target-1/ &&

2.43.GIT

In t9500 we're writing a custom configuration that sets up gitweb. This requires us to manually ensure that the repository format is configured as required, including both the repository format version and extensions. With the introduction of the "extensions.refStorage" extension we need to update the test to also write this new one.

---
 t/t9500-gitweb-standalone-no-errors.sh | 5 +++++
 1 file changed, 5 insertions(+)

index 0333065d4d..7679780fb8 100755
@@ -627,6 +627,7 @@ test_expect_success \
 test_expect_success 'setup' '
 	version=$(git config core.repositoryformatversion) &&
 	algo=$(test_might_fail git config extensions.objectformat) &&
+	refstorage=$(test_might_fail git config extensions.refstorage) &&
 	cat >.git/config <<-\EOF &&
 	# testing noval and alternate separator
 	[gitweb]

@@ -637,6 +638,10 @@ test_expect_success 'setup' '
 	if test -n "$algo"
 	then
 		git config extensions.objectformat "$algo"
+	fi &&
+	if test -n "$refstorage"
+	then
+		git config extensions.refstorage "$refstorage"
 	fi
 '
 

2.43.GIT

Hi,

this is the third version of my patch series that introduces the new refStorage extension. This extension will be used for the upcoming reftable backend.

Changes compared to v3:

- The ref_storage_format is now tracked as an unsigned int, proposed by Junio.

- Reworded the commit message in patch 2, proposed by Eric.

- Added a NEEDSWORK comment to get_worktrees_internal(), propose by Eric.

Thanks for your reviews!

Patrick

Patrick Steinhardt (12):
t: introduce DEFAULT_REPO_FORMAT prereq
worktree: skip reading HEAD when repairing worktrees
refs: refactor logic to look up storage backends
setup: start tracking ref storage format
setup: set repository's formats on init
setup: introduce "extensions.refStorage" extension
setup: introduce GIT_DEFAULT_REF_FORMAT envvar
t: introduce GIT_TEST_DEFAULT_REF_FORMAT envvar builtin/rev-parse: introduce --show-ref-format flag builtin/init: introduce --ref-format= value flag builtin/clone: introduce --ref-format= value flag
t9500: write "extensions.refstorage" into config

 Documentation/config/extensions.txt           | 11 +++
 Documentation/git-clone.txt                   |  6 ++
 Documentation/git-init.txt                    |  7 ++
 Documentation/git-rev-parse.txt               |  3 +
 Documentation/git.txt                         |  5 ++
 Documentation/ref-storage-format.txt          |  1 +
 .../technical/repository-version.txt          |  5 ++
 builtin/clone.c                               | 17 ++++-
 builtin/init-db.c                             | 15 +++-
 builtin/rev-parse.c                           |  4 ++
 refs.c                                        | 34 ++++++---
 refs.h                                        |  3 +
 refs/debug.c                                  |  1 -
 refs/files-backend.c                          |  1 -
 refs/packed-backend.c                         |  1 -
 refs/refs-internal.h                          |  1 -
 repository.c                                  |  6 ++
 repository.h                                  |  7 ++
 setup.c                                       | 66 +++++++++++++++--
 setup.h                                       | 10 ++-
 t/README                                      |  3 +
 t/t0001-init.sh                               | 70 +++++++++++++++++++
 t/t1500-rev-parse.sh                          | 17 +++++
 t/t3200-branch.sh                             |  2 +-
 t/t5601-clone.sh                              | 17 +++++
 t/t9500-gitweb-standalone-no-errors.sh        |  5 ++
 t/test-lib-functions.sh                       |  5 ++
 t/test-lib.sh                                 | 15 +++-
 worktree.c                                    | 31 +++++---
 29 files changed, 334 insertions(+), 35 deletions(-)
 create mode 100644 Documentation/ref-storage-format.txt

Range-diff against v2:

 1:  3613439cb7 =  1:  578deaabcf t: introduce DEFAULT_REPO_FORMAT prereq
 2:  ecf4f1ddee !  2:  77c7213c66 worktree: skip reading HEAD when repairing worktrees

@@ Commit message
is logic that we resolve their respective worktree HEADs, even though that information may not actually be needed in the end by all callers.

- In the context of git-init(1) this is about to become a problem, because
- we do not have a repository that was set up via setup_git_directory()
- or friends. Consequentially, it is not yet fully initialized at the time
- of calling repair_worktrees(), and properly setting up all parts of
- the repository in init_db() before we repair worktrees is not an easy
- thing to do. While this is okay right now where we only have a single
- reference backend in Git, once we gain a second one we would be trying
- to look up the worktree HEADs before we have figured out the reference
- format, which does not work.
+ Although not a problem presently with the file-based reference backend,
+ it will become a problem with the upcoming reftable backend. In the
+ context of git-init(1) we do not have a fully-initialized repository set
+ up via setup_git_directory() or friends. Consequently, we do not know
+ about the repository format when repair_worktrees() is called, and
+ properly setting up all parts of the repositroy in init_db() before we
+ try to repair worktrees is not an easy task. With the introduction of
+ the reftable backend, we would ultimately try to look up the worktree
+ HEADs before we have figured out the reference format, which does not
+ work.

We do not require the worktree HEADs at all to repair worktrees. So let's fix this issue by skipping over the step that reads them.
@@ worktree.c: static void mark_current_worktree(struct worktree **worktrees)
}

-struct worktree **get_worktrees(void)
++/*
++ * NEEDSWORK: This function exists so that we can look up metadata of a ++ * worktree without trying to access any of its internals like the refdb. It ++ * would be preferable to instead have a corruption-tolerant function for ++ * retrieving worktree metadata that could be used when the worktree is known ++ * to not be in a healthy state, e.g. when creating or repairing it. ++ */
+static struct worktree **get_worktrees_internal(int skip_reading_head)
{
struct worktree **list = NULL;
3: 12329b99b7 ! 3: 47649570bf refs: refactor logic to look up storage backends

    @@ refs.c
     +};
      
     -static struct ref_storage_be *find_ref_storage_backend(const char *name)
    -+static const struct ref_storage_be *find_ref_storage_backend(int ref_storage_format)
    ++static const struct ref_storage_be *find_ref_storage_backend(unsigned int ref_storage_format)
      {
     -	struct ref_storage_be *be;
     -	for (be = refs_backends; be; be = be->next)
    @@ refs.c
      	return NULL;
      }
      
    -+int ref_storage_format_by_name(const char *name)
    ++unsigned int ref_storage_format_by_name(const char *name)
     +{
    -+	for (int i = 0; i < ARRAY_SIZE(refs_backends); i++)
    ++	for (unsigned int i = 0; i < ARRAY_SIZE(refs_backends); i++)
     +		if (refs_backends[i] && !strcmp(refs_backends[i]->name, name))
     +			return i;
     +	return REF_STORAGE_FORMAT_UNKNOWN;
     +}
     +
    -+const char *ref_storage_format_to_name(int ref_storage_format)
    ++const char *ref_storage_format_to_name(unsigned int ref_storage_format)
     +{
     +	const struct ref_storage_be *be = find_ref_storage_backend(ref_storage_format);
     +	if (!be)
    @@ refs.c: static struct ref_store *ref_store_init(struct repository *repo,
      {
     -	const char *be_name = "files";
     -	struct ref_storage_be *be = find_ref_storage_backend(be_name);
    -+	int format = REF_STORAGE_FORMAT_FILES;
    ++	unsigned int format = REF_STORAGE_FORMAT_FILES;
     +	const struct ref_storage_be *be = find_ref_storage_backend(format);
      	struct ref_store *refs;
      
    @@ refs.h: struct string_list;
      struct string_list_item;
      struct worktree;
      
    -+int ref_storage_format_by_name(const char *name);
    -+const char *ref_storage_format_to_name(int ref_storage_format);
    ++unsigned int ref_storage_format_by_name(const char *name);
    ++const char *ref_storage_format_to_name(unsigned int ref_storage_format);
     +
      /*
       * Resolve a reference, recursively following symbolic refererences.
 4:  ddd099fbaf !  4:  837764d0b5 setup: start tracking ref storage format
    @@ refs.c: static struct ref_store *ref_store_init(struct repository *repo,
      					const char *gitdir,
      					unsigned int flags)
      {
    --	int format = REF_STORAGE_FORMAT_FILES;
    +-	unsigned int format = REF_STORAGE_FORMAT_FILES;
     -	const struct ref_storage_be *be = find_ref_storage_backend(format);
     +	const struct ref_storage_be *be;
      	struct ref_store *refs;
    @@ repository.c: void repo_set_hash_algo(struct repository *repo, int hash_algo)
      	repo->hash_algo = &hash_algos[hash_algo];
      }
      
    -+void repo_set_ref_storage_format(struct repository *repo, int format)
    ++void repo_set_ref_storage_format(struct repository *repo, unsigned int format)
     +{
     +	repo->ref_storage_format = format;
     +}
    @@ repository.h: struct repository {
      	const struct git_hash_algo *hash_algo;
      
     +	/* Repository's reference storage format, as serialized on disk. */
    -+	int ref_storage_format;
    ++	unsigned int ref_storage_format;
     +
      	/* A unique-id for tracing purposes. */
      	int trace2_repo_id;
    @@ repository.h: void repo_set_gitdir(struct repository *repo, const char *root,
      		     const struct set_gitdir_args *extra_args);
      void repo_set_worktree(struct repository *repo, const char *path);
      void repo_set_hash_algo(struct repository *repo, int algo);
    -+void repo_set_ref_storage_format(struct repository *repo, int format);
    ++void repo_set_ref_storage_format(struct repository *repo, unsigned int format);
      void initialize_the_repository(void);
      RESULT_MUST_BE_USED
      int repo_init(struct repository *r, const char *gitdir, const char *worktree);
    @@ setup.c: static int is_reinit(void)
      }
      
     -void create_reference_database(const char *initial_branch, int quiet)
    -+void create_reference_database(int ref_storage_format,
    ++void create_reference_database(unsigned int ref_storage_format,
     +			       const char *initial_branch, int quiet)
      {
      	struct strbuf err = STRBUF_INIT;
    @@ setup.c: static void validate_hash_algorithm(struct repository_format *repo_fmt,
      	}
      }
      
    -+static void validate_ref_storage_format(struct repository_format *repo_fmt, int format)
    ++static void validate_ref_storage_format(struct repository_format *repo_fmt,
    ++					unsigned int format)
     +{
     +	if (repo_fmt->version >= 0 &&
     +	    format != REF_STORAGE_FORMAT_UNKNOWN &&
    @@ setup.c: static void validate_hash_algorithm(struct repository_format *repo_fmt,
      int init_db(const char *git_dir, const char *real_git_dir,
     -	    const char *template_dir, int hash, const char *initial_branch,
     +	    const char *template_dir, int hash,
    -+	    int ref_storage_format, const char *initial_branch,
    ++	    unsigned int ref_storage_format,
    ++	    const char *initial_branch,
      	    int init_shared_repository, unsigned int flags)
      {
      	int reinit;
    @@ setup.h: struct repository_format {
      	int worktree_config;
      	int is_bare;
      	int hash_algo;
    -+	int ref_storage_format;
    ++	unsigned int ref_storage_format;
      	int sparse_index;
      	char *work_tree;
      	struct string_list unknown_extensions;
    @@ setup.h: void check_repository_format(struct repository_format *fmt);
      
      int init_db(const char *git_dir, const char *real_git_dir,
      	    const char *template_dir, int hash_algo,
    -+	    int ref_storage_format,
    ++	    unsigned int ref_storage_format,
      	    const char *initial_branch, int init_shared_repository,
      	    unsigned int flags);
      void initialize_repository_version(int hash_algo, int reinit);
     -void create_reference_database(const char *initial_branch, int quiet);
    -+void create_reference_database(int ref_storage_format,
    ++void create_reference_database(unsigned int ref_storage_format,
     +			       const char *initial_branch, int quiet);
      
      /*
 5:  01a1e58a97 =  5:  a51da56d9b setup: set repository's formats on init
 6:  0a586fa648 !  6:  a1e03e4392 setup: introduce "extensions.refStorage" extension
    @@ setup.c: static enum extension_result handle_extension(const char *var,
      		data->hash_algo = format;
      		return EXTENSION_OK;
     +	} else if (!strcmp(ext, "refstorage")) {
    -+		int format;
    ++		unsigned int format;
     +
     +		if (!value)
     +			return config_error_nonbool(var);
    @@ setup.c: static int needs_work_tree_config(const char *git_dir, const char *work
      }
      
     -void initialize_repository_version(int hash_algo, int reinit)
    -+void initialize_repository_version(int hash_algo, int ref_storage_format,
    ++void initialize_repository_version(int hash_algo,
    ++				   unsigned int ref_storage_format,
     +				   int reinit)
      {
      	char repo_version_string[10];
    @@ setup.c: static int create_default_files(const char *template_path,
     
      ## setup.h ##
     @@ setup.h: int init_db(const char *git_dir, const char *real_git_dir,
    - 	    int ref_storage_format,
    + 	    unsigned int ref_storage_format,
      	    const char *initial_branch, int init_shared_repository,
      	    unsigned int flags);
     -void initialize_repository_version(int hash_algo, int reinit);
    -+void initialize_repository_version(int hash_algo, int ref_storage_format,
    ++void initialize_repository_version(int hash_algo,
    ++				   unsigned int ref_storage_format,
     +				   int reinit);
    - void create_reference_database(int ref_storage_format,
    + void create_reference_database(unsigned int ref_storage_format,
      			       const char *initial_branch, int quiet);

7: 6d8754f73a ! 7: 5ffc70e9be setup: introduce GIT_DEFAULT_REF_FORMAT envvar
@@ Documentation/git.txt: double-quotes and respecting backslash escapes. E.g., the

## setup.c ##
@@ setup.c: static void validate_hash_algorithm(struct repository_format *repo_fmt, int hash
-
- static void validate_ref_storage_format(struct repository_format *repo_fmt, int format)
+ static void validate_ref_storage_format(struct repository_format *repo_fmt,
+ unsigned int format)
{
+ const char *name = getenv("GIT_DEFAULT_REF_FORMAT");
+

 8:  c645932f3d =  8:  13c074acdf t: introduce GIT_TEST_DEFAULT_REF_FORMAT envvar
 9:  761d647770 =  9:  4ee3c9a2d1 builtin/rev-parse: introduce `--show-ref-format` flag
10:  e382b5bf08 ! 10:  25773e3560 builtin/init: introduce `--ref-format=` value flag
    @@ builtin/init-db.c: int cmd_init_db(int argc, const char **argv, const char *pref
     +	const char *ref_format = NULL;
      	const char *initial_branch = NULL;
      	int hash_algo = GIT_HASH_UNKNOWN;
    -+	int ref_storage_format = REF_STORAGE_FORMAT_UNKNOWN;
    ++	unsigned int ref_storage_format = REF_STORAGE_FORMAT_UNKNOWN;
      	int init_shared_repository = -1;
      	const struct option init_db_options[] = {
      		OPT_STRING(0, "template", &template_dir, N_("template-directory"),
11:  257233658d ! 11:  3f1cb6b9e5 builtin/clone: introduce `--ref-format=` value flag
    @@ builtin/clone.c: int cmd_clone(int argc, const char **argv, const char *prefix)
      	int submodule_progress;
      	int filter_submodules = 0;
      	int hash_algo;
    -+	int ref_storage_format = REF_STORAGE_FORMAT_UNKNOWN;
    ++	unsigned int ref_storage_format = REF_STORAGE_FORMAT_UNKNOWN;
      	const int do_not_override_repo_unix_permissions = -1;
      
      	struct transport_ls_refs_options transport_ls_refs_options =

12: b8cd06ec53 = 12: 2e7682b2f3 t9500: write "extensions.refstorage" into config

base-commit: e79552d19784ee7f4bbce278fe25f93fbda196fa

2.43.GIT

A limited number of tests require repositories to have the default repository format or otherwise they would fail to run, e.g. because they fail to detect the correct hash function. While the hash function is the only extension right now that creates problems like this, we are about to add a second extension for the ref format.

Introduce a new DEFAULT_REPO_FORMAT prereq that can easily be amended whenever we add new format extensions. Next to making any such changes easier on us, the prerequisite's name should also help to clarify the intent better.

---
 t/t3200-branch.sh | 2 +-
 t/test-lib.sh     | 4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

index 6a316f081e..de7d3014e4 100755
@@ -519,7 +519,7 @@ EOF
 
 mv .git/config .git/config-saved
 
-test_expect_success SHA1 'git branch -m q q2 without config should succeed' '
+test_expect_success DEFAULT_REPO_FORMAT 'git branch -m q q2 without config should succeed' '
 	git branch -m q q2 &&
 	git branch -m q2 q
 '

index 876b99562a..dc03f06b8e 100644
@@ -1936,6 +1936,10 @@ test_lazy_prereq SHA1 '
 	esac
 '
 
+test_lazy_prereq DEFAULT_REPO_FORMAT '
+	test_have_prereq SHA1
+'
+
 # Ensure that no test accidentally triggers a Git command
 # that runs the actual maintenance scheduler, affecting a user's
 # system permanently.

2.43.GIT

When calling git init --separate-git-dir=<new-path> on a preexisting repository, we move the Git directory of that repository to the new path specified by the user. If there are worktrees present in the repository, we need to repair the worktrees so that their gitlinks point to the new location of the repository.

This repair logic will load repositories via get_worktrees(), which will enumerate up and initialize all worktrees. Part of initialization is logic that we resolve their respective worktree HEADs, even though that information may not actually be needed in the end by all callers.

Although not a problem presently with the file-based reference backend, it will become a problem with the upcoming reftable backend. In the context of git-init(1) we do not have a fully-initialized repository set up via setup_git_directory() or friends. Consequently, we do not know about the repository format when repair_worktrees() is called, and properly setting up all parts of the repositroy in init_db() before we try to repair worktrees is not an easy task. With the introduction of the reftable backend, we would ultimately try to look up the worktree HEADs before we have figured out the reference format, which does not work.

We do not require the worktree HEADs at all to repair worktrees. So let's fix this issue by skipping over the step that reads them.

---
 worktree.c | 31 +++++++++++++++++++++++--------
 1 file changed, 23 insertions(+), 8 deletions(-)

index a56a6c2a3d..cc34a3419b 100644
@@ -51,7 +51,7 @@ static void add_head_info(struct worktree *wt)
 /**
  * get the main worktree
  */
-static struct worktree *get_main_worktree(void)
+static struct worktree *get_main_worktree(int skip_reading_head)
 {
 	struct worktree *worktree = NULL;
 	struct strbuf worktree_path = STRBUF_INIT;

@@ -70,11 +70,13 @@ static struct worktree *get_main_worktree(void)
 	 */
 	worktree->is_bare = (is_bare_repository_cfg == 1) ||
 		is_bare_repository();
-	add_head_info(worktree);
+	if (!skip_reading_head)
+		add_head_info(worktree);
 	return worktree;
 }
 
-static struct worktree *get_linked_worktree(const char *id)
+static struct worktree *get_linked_worktree(const char *id,
+					    int skip_reading_head)
 {
 	struct worktree *worktree = NULL;
 	struct strbuf path = STRBUF_INIT;

@@ -93,7 +95,8 @@ static struct worktree *get_linked_worktree(const char *id)
 	CALLOC_ARRAY(worktree, 1);
 	worktree->path = strbuf_detach(&worktree_path, NULL);
 	worktree->id = xstrdup(id);
-	add_head_info(worktree);
+	if (!skip_reading_head)
+		add_head_info(worktree);
 
 done:
 	strbuf_release(&path);

@@ -118,7 +121,14 @@ static void mark_current_worktree(struct worktree **worktrees)
 	free(git_dir);
 }
 
-struct worktree **get_worktrees(void)
+/*
+ * NEEDSWORK: This function exists so that we can look up metadata of a
+ * worktree without trying to access any of its internals like the refdb. It
+ * would be preferable to instead have a corruption-tolerant function for
+ * retrieving worktree metadata that could be used when the worktree is known
+ * to not be in a healthy state, e.g. when creating or repairing it.
+ */
+static struct worktree **get_worktrees_internal(int skip_reading_head)
 {
 	struct worktree **list = NULL;
 	struct strbuf path = STRBUF_INIT;

@@ -128,7 +138,7 @@ struct worktree **get_worktrees(void)
 
 	ALLOC_ARRAY(list, alloc);
 
-	list[counter++] = get_main_worktree();
+	list[counter++] = get_main_worktree(skip_reading_head);
 
 	strbuf_addf(&path, "%s/worktrees", get_git_common_dir());
 	dir = opendir(path.buf);

@@ -137,7 +147,7 @@ struct worktree **get_worktrees(void)
 		while ((d = readdir_skip_dot_and_dotdot(dir)) != NULL) {
 			struct worktree *linked = NULL;
 
-			if ((linked = get_linked_worktree(d->d_name))) {
+			if ((linked = get_linked_worktree(d->d_name, skip_reading_head))) {
 				ALLOC_GROW(list, counter + 1, alloc);
 				list[counter++] = linked;
 			}

@@ -151,6 +161,11 @@ struct worktree **get_worktrees(void)
 	return list;
 }
 
+struct worktree **get_worktrees(void)
+{
+	return get_worktrees_internal(0);
+}
+
 const char *get_worktree_git_dir(const struct worktree *wt)
 {
 	if (!wt)

@@ -591,7 +606,7 @@ static void repair_noop(int iserr UNUSED,
 
 void repair_worktrees(worktree_repair_fn fn, void *cb_data)
 {
-	struct worktree **worktrees = get_worktrees();
+	struct worktree **worktrees = get_worktrees_internal(1);
 	struct worktree **wt = worktrees + 1; /* +1 skips main worktree */
 
 	if (!fn)

2.43.GIT

In order to look up ref storage backends, we're currently using a linked list of backends, where each backend is expected to set up its next pointer to the next ref storage backend. This is kind of a weird setup as backends need to be aware of other backends without much of a reason.

Refactor the code so that the array of backends is centrally defined in "refs.c", where each backend is now identified by an integer constant. Expose functions to translate from those integer constants to the name and vice versa, which will be required by subsequent patches.

---
 refs.c                | 34 +++++++++++++++++++++++++---------
 refs.h                |  3 +++
 refs/debug.c          |  1 -
 refs/files-backend.c  |  1 -
 refs/packed-backend.c |  1 -
 refs/refs-internal.h  |  1 -
 repository.h          |  3 +++
 7 files changed, 31 insertions(+), 13 deletions(-)

index 16bfa21df7..dea3d5c9a0 100644
@@ -33,17 +33,33 @@
 /*
  * List of all available backends
  */
-static struct ref_storage_be *refs_backends = &refs_be_files;
+static const struct ref_storage_be *refs_backends[] = {
+	[REF_STORAGE_FORMAT_FILES] = &refs_be_files,
+};
 
-static struct ref_storage_be *find_ref_storage_backend(const char *name)
+static const struct ref_storage_be *find_ref_storage_backend(unsigned int ref_storage_format)
 {
-	struct ref_storage_be *be;
-	for (be = refs_backends; be; be = be->next)
-		if (!strcmp(be->name, name))
-			return be;
+	if (ref_storage_format < ARRAY_SIZE(refs_backends))
+		return refs_backends[ref_storage_format];
 	return NULL;
 }
 
+unsigned int ref_storage_format_by_name(const char *name)
+{
+	for (unsigned int i = 0; i < ARRAY_SIZE(refs_backends); i++)
+		if (refs_backends[i] && !strcmp(refs_backends[i]->name, name))
+			return i;
+	return REF_STORAGE_FORMAT_UNKNOWN;
+}
+
+const char *ref_storage_format_to_name(unsigned int ref_storage_format)
+{
+	const struct ref_storage_be *be = find_ref_storage_backend(ref_storage_format);
+	if (!be)
+		return "unknown";
+	return be->name;
+}
+
 /*
  * How to handle various characters in refnames:
  * 0: An acceptable character for refs

@@ -2029,12 +2045,12 @@ static struct ref_store *ref_store_init(struct repository *repo,
 					const char *gitdir,
 					unsigned int flags)
 {
-	const char *be_name = "files";
-	struct ref_storage_be *be = find_ref_storage_backend(be_name);
+	unsigned int format = REF_STORAGE_FORMAT_FILES;
+	const struct ref_storage_be *be = find_ref_storage_backend(format);
 	struct ref_store *refs;
 
 	if (!be)
-		BUG("reference backend %s is unknown", be_name);
+		BUG("reference backend is unknown");
 
 	refs = be->init(repo, gitdir, flags);
 	return refs;

index ff113bb12a..11b3b6ccea 100644
@@ -11,6 +11,9 @@ struct string_list;
 struct string_list_item;
 struct worktree;
 
+unsigned int ref_storage_format_by_name(const char *name);
+const char *ref_storage_format_to_name(unsigned int ref_storage_format);
+
 /*
  * Resolve a reference, recursively following symbolic refererences.
  *

index 83b7a0ba65..b9775f2c37 100644
@@ -426,7 +426,6 @@ static int debug_reflog_expire(struct ref_store *ref_store, const char *refname,
 }
 
 struct ref_storage_be refs_be_debug = {
-	.next = NULL,
 	.name = "debug",
 	.init = NULL,
 	.init_db = debug_init_db,

index ad8b1d143f..43fd0ac760 100644
@@ -3241,7 +3241,6 @@ static int files_init_db(struct ref_store *ref_store, struct strbuf *err UNUSED)
 }
 
 struct ref_storage_be refs_be_files = {
-	.next = NULL,
 	.name = "files",
 	.init = files_ref_store_create,
 	.init_db = files_init_db,

index b9fa097a29..8d1090e284 100644
@@ -1705,7 +1705,6 @@ static struct ref_iterator *packed_reflog_iterator_begin(struct ref_store *ref_s
 }
 
 struct ref_storage_be refs_be_packed = {
-	.next = NULL,
 	.name = "packed",
 	.init = packed_ref_store_create,
 	.init_db = packed_init_db,

index 4af83bf9a5..8e9f04cc67 100644
@@ -663,7 +663,6 @@ typedef int read_symbolic_ref_fn(struct ref_store *ref_store, const char *refnam
 				 struct strbuf *referent);
 
 struct ref_storage_be {
-	struct ref_storage_be *next;
 	const char *name;
 	ref_store_init_fn *init;
 	ref_init_db_fn *init_db;

index 5f18486f64..ea4c488b81 100644
@@ -24,6 +24,9 @@ enum fetch_negotiation_setting {
 	FETCH_NEGOTIATION_NOOP,
 };
 
+#define REF_STORAGE_FORMAT_UNKNOWN 0
+#define REF_STORAGE_FORMAT_FILES   1
+
 struct repo_settings {
 	int initialized;
 

2.43.GIT

In order to discern which ref storage format a repository is supposed to use we need to start setting up and/or discovering the format. This needs to happen in two separate code paths.

- The first path is when we create a repository via init_db(). When we are re-initializing a preexisting repository we need to retain the previously used ref storage format -- if the user asked for a different format then this indicates an error and we error out. Otherwise we either initialize the repository with the format asked for by the user or the default format, which currently is the "files" backend.

- The second path is when discovering repositories, where we need to read the config of that repository. There is not yet any way to configure something other than the "files" backend, so we can just blindly set the ref storage format to this backend.

Wire up this logic so that we have the ref storage format always readily available when needed. As there is only a single backend and because it is not configurable we cannot yet verify that this tracking works as expected via tests, but tests will be added in subsequent commits. To countermand this ommission now though, raise a BUG() in case the ref storage format is not set up properly in ref_store_init().

---
 builtin/clone.c   |  5 +++--
 builtin/init-db.c |  4 +++-
 refs.c            |  4 ++--
 repository.c      |  6 ++++++
 repository.h      |  4 ++++
 setup.c           | 28 +++++++++++++++++++++++++---
 setup.h           |  6 +++++-
 7 files changed, 48 insertions(+), 9 deletions(-)

index 343f536cf8..48aeb1b90b 100644
@@ -1107,7 +1107,8 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	 * repository, and reference backends may persist that information into
 	 * their on-disk data structures.
 	 */
-	init_db(git_dir, real_git_dir, option_template, GIT_HASH_UNKNOWN, NULL,
+	init_db(git_dir, real_git_dir, option_template, GIT_HASH_UNKNOWN,
+		REF_STORAGE_FORMAT_UNKNOWN, NULL,
 		do_not_override_repo_unix_permissions, INIT_DB_QUIET | INIT_DB_SKIP_REFDB);
 
 	if (real_git_dir) {

@@ -1292,7 +1293,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	hash_algo = hash_algo_by_ptr(transport_get_hash_algo(transport));
 	initialize_repository_version(hash_algo, 1);
 	repo_set_hash_algo(the_repository, hash_algo);
-	create_reference_database(NULL, 1);
+	create_reference_database(the_repository->ref_storage_format, NULL, 1);
 
 	/*
 	 * Before fetching from the remote, download and install bundle

index cb727c826f..b6e80feab6 100644
@@ -11,6 +11,7 @@
 #include "object-file.h"
 #include "parse-options.h"
 #include "path.h"
+#include "refs.h"
 #include "setup.h"
 #include "strbuf.h"
 

@@ -236,5 +237,6 @@ int cmd_init_db(int argc, const char **argv, const char *prefix)
 
 	flags |= INIT_DB_EXIST_OK;
 	return init_db(git_dir, real_git_dir, template_dir, hash_algo,
-		       initial_branch, init_shared_repository, flags);
+		       REF_STORAGE_FORMAT_UNKNOWN, initial_branch,
+		       init_shared_repository, flags);
 }

index dea3d5c9a0..fdbf5f4cb1 100644
@@ -2045,10 +2045,10 @@ static struct ref_store *ref_store_init(struct repository *repo,
 					const char *gitdir,
 					unsigned int flags)
 {
-	unsigned int format = REF_STORAGE_FORMAT_FILES;
-	const struct ref_storage_be *be = find_ref_storage_backend(format);
+	const struct ref_storage_be *be;
 	struct ref_store *refs;
 
+	be = find_ref_storage_backend(repo->ref_storage_format);
 	if (!be)
 		BUG("reference backend is unknown");
 

index a7679ceeaa..d7d24d416a 100644
@@ -104,6 +104,11 @@ void repo_set_hash_algo(struct repository *repo, int hash_algo)
 	repo->hash_algo = &hash_algos[hash_algo];
 }
 
+void repo_set_ref_storage_format(struct repository *repo, unsigned int format)
+{
+	repo->ref_storage_format = format;
+}
+
 /*
  * Attempt to resolve and set the provided 'gitdir' for repository 'repo'.
  * Return 0 upon success and a non-zero value upon failure.

@@ -184,6 +189,7 @@ int repo_init(struct repository *repo,
 		goto error;
 
 	repo_set_hash_algo(repo, format.hash_algo);
+	repo_set_ref_storage_format(repo, format.ref_storage_format);
 	repo->repository_format_worktree_config = format.worktree_config;
 
 	/* take ownership of format.partial_clone */

index ea4c488b81..f5269b3730 100644
@@ -163,6 +163,9 @@ struct repository {
 	/* Repository's current hash algorithm, as serialized on disk. */
 	const struct git_hash_algo *hash_algo;
 
+	/* Repository's reference storage format, as serialized on disk. */
+	unsigned int ref_storage_format;
+
 	/* A unique-id for tracing purposes. */
 	int trace2_repo_id;
 

@@ -202,6 +205,7 @@ void repo_set_gitdir(struct repository *repo, const char *root,
 		     const struct set_gitdir_args *extra_args);
 void repo_set_worktree(struct repository *repo, const char *path);
 void repo_set_hash_algo(struct repository *repo, int algo);
+void repo_set_ref_storage_format(struct repository *repo, unsigned int format);
 void initialize_the_repository(void);
 RESULT_MUST_BE_USED
 int repo_init(struct repository *r, const char *gitdir, const char *worktree);

index bc90bbd033..9c9a167f52 100644
@@ -1566,6 +1566,8 @@ const char *setup_git_directory_gently(int *nongit_ok)
 		}
 		if (startup_info->have_repository) {
 			repo_set_hash_algo(the_repository, repo_fmt.hash_algo);
+			repo_set_ref_storage_format(the_repository,
+						    repo_fmt.ref_storage_format);
 			the_repository->repository_format_worktree_config =
 				repo_fmt.worktree_config;
 			/* take ownership of repo_fmt.partial_clone */

@@ -1659,6 +1661,8 @@ void check_repository_format(struct repository_format *fmt)
 	check_repository_format_gently(get_git_dir(), fmt, NULL);
 	startup_info->have_repository = 1;
 	repo_set_hash_algo(the_repository, fmt->hash_algo);
+	repo_set_ref_storage_format(the_repository,
+				    fmt->ref_storage_format);
 	the_repository->repository_format_worktree_config =
 		fmt->worktree_config;
 	the_repository->repository_format_partial_clone =

@@ -1899,7 +1903,8 @@ static int is_reinit(void)
 	return ret;
 }
 
-void create_reference_database(const char *initial_branch, int quiet)
+void create_reference_database(unsigned int ref_storage_format,
+			       const char *initial_branch, int quiet)
 {
 	struct strbuf err = STRBUF_INIT;
 	int reinit = is_reinit();

@@ -1919,6 +1924,7 @@ void create_reference_database(const char *initial_branch, int quiet)
 	safe_create_dir(git_path("refs"), 1);
 	adjust_shared_perm(git_path("refs"));
 
+	repo_set_ref_storage_format(the_repository, ref_storage_format);
 	if (refs_init_db(&err))
 		die("failed to set up refs db: %s", err.buf);
 

@@ -2137,8 +2143,22 @@ static void validate_hash_algorithm(struct repository_format *repo_fmt, int hash
 	}
 }
 
+static void validate_ref_storage_format(struct repository_format *repo_fmt,
+					unsigned int format)
+{
+	if (repo_fmt->version >= 0 &&
+	    format != REF_STORAGE_FORMAT_UNKNOWN &&
+	    format != repo_fmt->ref_storage_format) {
+		die(_("attempt to reinitialize repository with different reference storage format"));
+	} else if (format != REF_STORAGE_FORMAT_UNKNOWN) {
+		repo_fmt->ref_storage_format = format;
+	}
+}
+
 int init_db(const char *git_dir, const char *real_git_dir,
-	    const char *template_dir, int hash, const char *initial_branch,
+	    const char *template_dir, int hash,
+	    unsigned int ref_storage_format,
+	    const char *initial_branch,
 	    int init_shared_repository, unsigned int flags)
 {
 	int reinit;

@@ -2181,13 +2201,15 @@ int init_db(const char *git_dir, const char *real_git_dir,
 	check_repository_format(&repo_fmt);
 
 	validate_hash_algorithm(&repo_fmt, hash);
+	validate_ref_storage_format(&repo_fmt, ref_storage_format);
 
 	reinit = create_default_files(template_dir, original_git_dir,
 				      &repo_fmt, prev_bare_repository,
 				      init_shared_repository);
 
 	if (!(flags & INIT_DB_SKIP_REFDB))
-		create_reference_database(initial_branch, flags & INIT_DB_QUIET);
+		create_reference_database(repo_fmt.ref_storage_format,
+					  initial_branch, flags & INIT_DB_QUIET);
 	create_object_directory();
 
 	if (get_shared_repository()) {

index 3f0f17c351..3d3eda7967 100644
@@ -115,6 +115,7 @@ struct repository_format {
 	int worktree_config;
 	int is_bare;
 	int hash_algo;
+	unsigned int ref_storage_format;
 	int sparse_index;
 	char *work_tree;
 	struct string_list unknown_extensions;

@@ -131,6 +132,7 @@ struct repository_format {
 	.version = -1, \
 	.is_bare = -1, \
 	.hash_algo = GIT_HASH_SHA1, \
+	.ref_storage_format = REF_STORAGE_FORMAT_FILES, \
 	.unknown_extensions = STRING_LIST_INIT_DUP, \
 	.v1_only_extensions = STRING_LIST_INIT_DUP, \
 }

@@ -175,10 +177,12 @@ void check_repository_format(struct repository_format *fmt);
 
 int init_db(const char *git_dir, const char *real_git_dir,
 	    const char *template_dir, int hash_algo,
+	    unsigned int ref_storage_format,
 	    const char *initial_branch, int init_shared_repository,
 	    unsigned int flags);
 void initialize_repository_version(int hash_algo, int reinit);
-void create_reference_database(const char *initial_branch, int quiet);
+void create_reference_database(unsigned int ref_storage_format,
+			       const char *initial_branch, int quiet);
 
 /*
  * NOTE NOTE NOTE!!

2.43.GIT

The proper hash algorithm and ref storage format that will be used for a newly initialized repository will be figured out in init_db() via validate_hash_algorithm() and validate_ref_storage_format(). Until now though, we never set up the hash algorithm or ref storage format of the_repository accordingly.

There are only two callsites of init_db(), one in git-init(1) and one in git-clone(1). The former function doesn't care for the formats to be set up properly because it never access the repository after calling the function in the first place.

For git-clone(1) it's a different story though, as we call init_db() before listing remote refs. While we do indeed have the wrong hash function in the_repository when init_db() sets up a non-default object format for the repository, it never mattered because we adjust the hash after learning about the remote's hash function via the listed refs.

So the current state is correct for the hash algo, but it's not for the ref storage format because git-clone(1) wouldn't know to set it up properly. But instead of adjusting only the ref_storage_format, set both the hash algo and the ref storage format so that the_repository is in the correct state when init_db() exits. This is fine as we will adjust the hash later on anyway and makes it easier to reason about the end state of the_repository.

---
 setup.c | 7 +++++++
 1 file changed, 7 insertions(+)

index 9c9a167f52..49570e6b3a 100644
@@ -2207,6 +2207,13 @@ int init_db(const char *git_dir, const char *real_git_dir,
 				      &repo_fmt, prev_bare_repository,
 				      init_shared_repository);
 
+	/*
+	 * Now that we have set up both the hash algorithm and the ref storage
+	 * format we can update the repository's settings accordingly.
+	 */
+	repo_set_hash_algo(the_repository, repo_fmt.hash_algo);
+	repo_set_ref_storage_format(the_repository, repo_fmt.ref_storage_format);
+
 	if (!(flags & INIT_DB_SKIP_REFDB))
 		create_reference_database(repo_fmt.ref_storage_format,
 					  initial_branch, flags & INIT_DB_QUIET);

2.43.GIT

Introduce a new "extensions.refStorage" extension that allows us to specify the ref storage format used by a repository. For now, the only supported format is the "files" format, but this list will likely soon be extended to also support the upcoming "reftable" format.

There have been discussions on the Git mailing list in the past around how exactly this extension should look like. One alternative [1] that was discussed was whether it would make sense to model the extension in such a way that backends are arbitrarily stackable. This would allow for a combined value of e.g. "loose,packed-refs" or "loose,reftable", which indicates that new refs would be written via "loose" files backend and compressed into "packed-refs" or "reftable" backends, respectively.

It is arguable though whether this flexibility and the complexity that it brings with it is really required for now. It is not foreseeable that there will be a proliferation of backends in the near-term future, and the current set of existing formats and formats which are on the horizon can easily be configured with the much simpler proposal where we have a single value, only.

Furthermore, if we ever see that we indeed want to gain the ability to arbitrarily stack the ref formats, then we can adapt the current extension rather easily. Given that Git clients will refuse any unknown value for the "extensions.refStorage" extension they would also know to ignore a stacked "loose,packed-refs" in the future.

So let's stick with the easy proposal for the time being and wire up the extension.

[1]: <[email protected]>

---
 Documentation/config/extensions.txt           | 11 ++++++++
 Documentation/ref-storage-format.txt          |  1 +
 .../technical/repository-version.txt          |  5 ++++
 builtin/clone.c                               |  2 +-
 setup.c                                       | 24 ++++++++++++++---
 setup.h                                       |  4 ++-
 t/t0001-init.sh                               | 26 +++++++++++++++++++
 t/test-lib.sh                                 |  2 +-
 8 files changed, 69 insertions(+), 6 deletions(-)
 create mode 100644 Documentation/ref-storage-format.txt

index bccaec7a96..66db0e15da 100644
@@ -7,6 +7,17 @@ Note that this setting should only be set by linkgit:git-init[1] or
 linkgit:git-clone[1].  Trying to change it after initialization will not
 work and will produce hard-to-diagnose issues.
 
+extensions.refStorage::
+	Specify the ref storage format to use. The acceptable values are:
++
+include::../ref-storage-format.txt[]
++
+It is an error to specify this key unless `core.repositoryFormatVersion` is 1.
++
+Note that this setting should only be set by linkgit:git-init[1] or
+linkgit:git-clone[1]. Trying to change it after initialization will not
+work and will produce hard-to-diagnose issues.
+
 extensions.worktreeConfig::
 	If enabled, then worktrees will load config settings from the
 	`$GIT_DIR/config.worktree` file in addition to the

new file mode 100644
index 0000000000..1a65cac468
@@ -0,0 +1 @@
+* `files` for loose files with packed-refs. This is the default.

index 045a76756f..27be3741e6 100644
@@ -100,3 +100,8 @@ If set, by default "git config" reads from both "config" and
 multiple working directory mode, "config" file is shared while
 "config.worktree" is per-working directory (i.e., it's in
 GIT_COMMON_DIR/worktrees/<id>/config.worktree)
+
+==== `refStorage`
+
+Specifies the file format for the ref database. The only valid value
+is `files` (loose references with a packed-refs file).

index 48aeb1b90b..0fb3816d0c 100644
@@ -1291,7 +1291,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	 * ours to the same thing.
 	 */
 	hash_algo = hash_algo_by_ptr(transport_get_hash_algo(transport));
-	initialize_repository_version(hash_algo, 1);
+	initialize_repository_version(hash_algo, the_repository->ref_storage_format, 1);
 	repo_set_hash_algo(the_repository, hash_algo);
 	create_reference_database(the_repository->ref_storage_format, NULL, 1);
 

index 49570e6b3a..fb1413cabd 100644
@@ -592,6 +592,17 @@ static enum extension_result handle_extension(const char *var,
 				     "extensions.objectformat", value);
 		data->hash_algo = format;
 		return EXTENSION_OK;
+	} else if (!strcmp(ext, "refstorage")) {
+		unsigned int format;
+
+		if (!value)
+			return config_error_nonbool(var);
+		format = ref_storage_format_by_name(value);
+		if (format == REF_STORAGE_FORMAT_UNKNOWN)
+			return error(_("invalid value for '%s': '%s'"),
+				     "extensions.refstorage", value);
+		data->ref_storage_format = format;
+		return EXTENSION_OK;
 	}
 	return EXTENSION_UNKNOWN;
 }

@@ -1871,12 +1882,15 @@ static int needs_work_tree_config(const char *git_dir, const char *work_tree)
 	return 1;
 }
 
-void initialize_repository_version(int hash_algo, int reinit)
+void initialize_repository_version(int hash_algo,
+				   unsigned int ref_storage_format,
+				   int reinit)
 {
 	char repo_version_string[10];
 	int repo_version = GIT_REPO_VERSION;
 
-	if (hash_algo != GIT_HASH_SHA1)
+	if (hash_algo != GIT_HASH_SHA1 ||
+	    ref_storage_format != REF_STORAGE_FORMAT_FILES)
 		repo_version = GIT_REPO_VERSION_READ;
 
 	/* This forces creation of new config file */

@@ -1889,6 +1903,10 @@ void initialize_repository_version(int hash_algo, int reinit)
 			       hash_algos[hash_algo].name);
 	else if (reinit)
 		git_config_set_gently("extensions.objectformat", NULL);
+
+	if (ref_storage_format != REF_STORAGE_FORMAT_FILES)
+		git_config_set("extensions.refstorage",
+			       ref_storage_format_to_name(ref_storage_format));
 }
 
 static int is_reinit(void)

@@ -2030,7 +2048,7 @@ static int create_default_files(const char *template_path,
 		adjust_shared_perm(get_git_dir());
 	}
 
-	initialize_repository_version(fmt->hash_algo, 0);
+	initialize_repository_version(fmt->hash_algo, fmt->ref_storage_format, 0);
 
 	/* Check filemode trustability */
 	path = git_path_buf(&buf, "config");

index 3d3eda7967..3599aec93c 100644
@@ -180,7 +180,9 @@ int init_db(const char *git_dir, const char *real_git_dir,
 	    unsigned int ref_storage_format,
 	    const char *initial_branch, int init_shared_repository,
 	    unsigned int flags);
-void initialize_repository_version(int hash_algo, int reinit);
+void initialize_repository_version(int hash_algo,
+				   unsigned int ref_storage_format,
+				   int reinit);
 void create_reference_database(unsigned int ref_storage_format,
 			       const char *initial_branch, int quiet);