btrfs-progs: allow use of subvolume id to create snapshots

This patch uses the new BTRFS_SUBVOL_CREATE_SUBVOLID flag to create snapshots by subvolume ID.

usage: btrfs subvolume snapshot [-r] [-q <qgroupid>] -s <subvolid> <dest>/<name>

Since we don't have a name for the source snapshot, the complete path to the destination must be specified.

A previous version of this patch missed an error printing case and would print (null) instead of the subvolume id on error.

Signed-off-by Jeff Mahoney <[email protected]>

---
 cmds-subvolume.c |  105 +++++++++++++++++++++++++++++++++++++++++--------------
 ioctl.h          |    6 ++-
 man/btrfs.8.in   |   31 ++++++++++++++--
 3 files changed, 112 insertions(+), 30 deletions(-)

cmds-subvolume.c +79 -26

@@ -14,6 +14,7 @@
  * Boston, MA 021110-1307, USA.
  */
 
+#define _GNU_SOURCE
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>

@@ -576,6 +577,7 @@ out:
 static const char * const cmd_snapshot_usage[] = {
 	"btrfs subvolume snapshot [-r] <source> <dest>|[<dest>/]<name>",
 	"btrfs subvolume snapshot [-r] [-i <qgroupid>] <source> <dest>|[<dest>/]<name>",
+	"btrfs subvolume snapshot [-r] [-i <qgroupid>] -s <subvolid> <dest>/<name>",
 	"Create a snapshot of the subvolume",
 	"Create a writable/readonly snapshot of the subvolume <source> with",
 	"the name <name> in the <dest> directory.  If only <dest> is given,",

@@ -584,12 +586,27 @@ static const char * const cmd_snapshot_u
 	"-r             create a readonly snapshot",
 	"-i <qgroupid>  add the newly created snapshot to a qgroup. This",
 	"               option can be given multiple times.",
+	"-s <subvolid>  create a snapshot using the subvolume id. This",
+	"               is useful for snapshotting subvolumes outside",
+	"               of the mounted namespace.",
 	NULL
 };
 
+static int get_subvolid(const char *str, u64 *subvolid)
+{
+	char *p;
+	errno = 0;
+	*subvolid = strtoull(optarg, &p, 10);
+	if (errno || *p != '\0') {
+		fprintf(stderr, "ERROR: invalid subvolume id '%s'\n", optarg);
+		return -EINVAL;
+	}
+	return 0;
+}
+
 static int cmd_snapshot(int argc, char **argv)
 {
-	char	*subvol, *dst;
+	char	*subvol = NULL, *dst;
 	int	res, retval;
 	int	fd = -1, fddst = -1;
 	int	len, readonly = 0;

@@ -597,6 +614,9 @@ static int cmd_snapshot(int argc, char *
 	char	*dupdir = NULL;
 	char	*newname;
 	char	*dstdir;
+	u64	subvolid = 0;
+	char	*subvol_descr = NULL;
+	int	nargs = 2;
 	struct btrfs_ioctl_vol_args_v2	args;
 	struct btrfs_qgroup_inherit *inherit = NULL;
 	DIR *dirstream1 = NULL, *dirstream2 = NULL;

@@ -604,7 +624,7 @@ static int cmd_snapshot(int argc, char *
 	optind = 1;
 	memset(&args, 0, sizeof(args));
 	while (1) {
-		int c = getopt(argc, argv, "c:i:r");
+		int c = getopt(argc, argv, "c:i:rs:");
 		if (c < 0)
 			break;
 

@@ -633,27 +653,39 @@ static int cmd_snapshot(int argc, char *
 				goto out;
 			}
 			break;
+		case 's':
+			res = get_subvolid(optarg, &subvolid);
+			if (res) {
+				retval = res;
+				goto out;
+			}
+			nargs = 1;
+			break;
 		default:
 			usage(cmd_snapshot_usage);
 		}
 	}
 
-	if (check_argc_exact(argc - optind, 2))
+	if (check_argc_exact(argc - optind, nargs))
 		usage(cmd_snapshot_usage);
 
-	subvol = argv[optind];
-	dst = argv[optind + 1];
+	if (nargs == 2) {
+		subvol = argv[optind];
+		dst = argv[optind + 1];
 
-	retval = 1;	/* failure */
-	res = test_issubvolume(subvol);
-	if (res < 0) {
-		fprintf(stderr, "ERROR: error accessing '%s'\n", subvol);
-		goto out;
-	}
-	if (!res) {
-		fprintf(stderr, "ERROR: '%s' is not a subvolume\n", subvol);
-		goto out;
-	}
+		retval = 1;	/* failure */
+		res = test_issubvolume(subvol);
+		if (res < 0) {
+			fprintf(stderr, "ERROR: error accessing '%s'\n", subvol);
+			goto out;
+		}
+		if (!res) {
+			fprintf(stderr, "ERROR: '%s' is not a subvolume\n",
+				subvol);
+			goto out;
+		}
+	} else
+		dst = argv[optind];
 
 	res = test_isdir(dst);
 	if (res == 0) {

@@ -662,6 +694,13 @@ static int cmd_snapshot(int argc, char *
 	}
 
 	if (res > 0) {
+		if (!subvol) {
+			retval = 1;
+			fprintf(stderr,
+				"ERROR: '%s' exists and must not when snapshotting by specifying subvolid.\n",
+				dst);
+			goto out;
+		}
 		dupname = strdup(subvol);
 		newname = basename(dupname);
 		dstdir = dst;

@@ -692,22 +731,34 @@ static int cmd_snapshot(int argc, char *
 		goto out;
 	}
 
-	fd = open_file_or_dir(subvol, &dirstream2);
-	if (fd < 0) {
-		fprintf(stderr, "ERROR: can't access '%s'\n", dstdir);
+	if (subvol) {
+		fd = open_file_or_dir(subvol, &dirstream2);
+		if (fd < 0) {
+			fprintf(stderr, "ERROR: can't access '%s'\n", dstdir);
+			goto out;
+		}
+		args.fd = fd;
+		res = asprintf(&subvol_descr, "'%s'", subvol);
+	} else {
+		args.subvolid = subvolid;
+		args.flags |= BTRFS_SUBVOL_CREATE_SUBVOLID;
+		res = asprintf(&subvol_descr, "subvolume id %llu", subvolid);
+	}
+	if (res < 0) {
+		fprintf(stderr, "ERROR: can't allocate memory\n");
+		retval = 1;
 		goto out;
 	}
 
 	if (readonly) {
 		args.flags |= BTRFS_SUBVOL_RDONLY;
-		printf("Create a readonly snapshot of '%s' in '%s/%s'\n",
-		       subvol, dstdir, newname);
+		printf("Create a readonly snapshot of %s in '%s/%s'\n",
+		       subvol_descr, dstdir, newname);
 	} else {
-		printf("Create a snapshot of '%s' in '%s/%s'\n",
-		       subvol, dstdir, newname);
+		printf("Create a snapshot of %s in '%s/%s'\n",
+		       subvol_descr, dstdir, newname);
 	}
 
-	args.fd = fd;
 	if (inherit) {
 		args.flags |= BTRFS_SUBVOL_QGROUP_INHERIT;
 		args.size = qgroup_inherit_size(inherit);

@@ -718,8 +769,8 @@ static int cmd_snapshot(int argc, char *
 	res = ioctl(fddst, BTRFS_IOC_SNAP_CREATE_V2, &args);
 
 	if (res < 0) {
-		fprintf( stderr, "ERROR: cannot snapshot '%s' - %s\n",
-			subvol, strerror(errno));
+		fprintf( stderr, "ERROR: cannot snapshot %s - %s\n",
+			subvol_descr, strerror(errno));
 		goto out;
 	}
 

@@ -727,7 +778,9 @@ static int cmd_snapshot(int argc, char *
 
 out:
 	close_file_or_dir(fddst, dirstream1);
-	close_file_or_dir(fd, dirstream2);
+	if (subvol)
+		close_file_or_dir(fd, dirstream2);
+	free(subvol_descr);
 	free(inherit);
 	free(dupname);
 	free(dupdir);

ioctl.h +5 -1

@@ -41,6 +41,7 @@ struct btrfs_ioctl_vol_args {
 #define BTRFS_SUBVOL_CREATE_ASYNC	(1ULL << 0)
 #define BTRFS_SUBVOL_RDONLY		(1ULL << 1)
 #define BTRFS_SUBVOL_QGROUP_INHERIT	(1ULL << 2)
+#define BTRFS_SUBVOL_CREATE_SUBVOLID	(1ULL << 3)
 
 #define BTRFS_QGROUP_INHERIT_SET_LIMITS	(1ULL << 0)
 

@@ -69,7 +70,10 @@ struct btrfs_ioctl_qgroup_limit_args {
 #define BTRFS_SUBVOL_NAME_MAX 4039
 
 struct btrfs_ioctl_vol_args_v2 {
-	__s64 fd;
+	union {
+		__s64 fd;
+		__u64 subvolid;
+	};
 	__u64 transid;
 	__u64 flags;
 	union {

man/btrfs.8.in +28 -3

@@ -12,7 +12,9 @@ btrfs \- control a btrfs filesystem
 .PP
 \fBbtrfs\fP \fBsubvolume list\fP [\fIoptions\fP] [-G [+|-]\fIvalue\fP] [-C [+|-]\fIvalue\fP] [--sort=rootid,gen,ogen,path] \fI<path>\fP
 .PP
-\fBbtrfs\fP \fBsubvolume snapshot\fP [-r] \fI<source>\fP \fI<dest>\fP|[\fI<dest>\fP/]\fI<name>\fP
+\fBbtrfs\fP \fBsubvolume snapshot\fP [-r] [-i qgroupid] \fI<source>\fP \fI<dest>\fP|[\fI<dest>\fP/]\fI<name>\fP
+.PP
+\fBbtrfs\fP \fBsubvolume snapshot\fP [-r] [-i qgroupid] \fI-s <subvolid>\fP \fI<dest>/<name>\fP
 .PP
 \fBbtrfs\fP \fBsubvolume get-default\fP\fI <path>\fP
 .PP

@@ -242,12 +244,35 @@ for \fB--sort\fP you can combine some it
 .RE
 .TP
 
-\fBsubvolume snapshot\fP [-r] \fI<source>\fP \fI<dest>\fP|[\fI<dest>\fP/]\fI<name>\fP
+\fBsubvolume snapshot\fP [-r] [-i qgroupid] \fI<source>\fP \fI<dest>\fP|[\fI<dest>\fP/]\fI<name>\fP
 Create a writable/readonly snapshot of the subvolume \fI<source>\fR with the
 name \fI<name>\fR in the \fI<dest>\fR directory.
 If only \fI<dest>\fR is given, the subvolume will be named the basename of \fI<source>\fR.
 If \fI<source>\fR is not a subvolume, \fBbtrfs\fR returns an error.
-If \fI-r\fR is given, the snapshot will be readonly.
+.RS
+
+\fIOptions\fP
+.IP \fB-r\fP 5
+The newly created snapshot will be readonly.
+.IP "\fB-i\fP \fI<qgroupid>\fR" 5
+Add the newly created subvolume to a qgroup. This option can be given multiple
+times.
+.RE
+.TP
+
+\fBsubvolume snapshot\fP [-r] [-i qgroupid] \fI-s <subvolid>\fP \fI<dest>\fP/\fI<name>\fP
+Create a writable/readonly snapshot of the subvolume \fI<subvolid>\fR with the
+name \fI<name>\fR in the \fI<dest>\fR directory.
+If \fI<subvolid>\fR does not refer to a subvolume, \fBbtrfs\fR returns an error.
+.RS
+
+\fIOptions\fP
+.IP \fB-r\fP 5
+The newly created snapshot will be readonly.
+.IP "\fB-i\fP \fI<qgroupid>\fR" 5
+Add the newly created subvolume to a qgroup. This option can be given multiple
+times.
+.RE
 .TP
 
 \fBsubvolume get-default\fR\fI <path>\fR

Quoted 9 lines · Jeff Mahoney

This patch uses the new BTRFS_SUBVOL_CREATE_SUBVOLID flag to create snapshots by subvolume ID.

usage: btrfs subvolume snapshot [-r] [-q <qgroupid>] -s <subvolid> <dest>/<name>

Since we don't have a name for the source snapshot, the complete path to the destination must be specified.

Quoted 2 lines

A previous version of this patch missed an error printing case and would print (null) instead of the subvolume id on error.

It's interesting you're doing it this way around. For the (fairly common) "regular snapshots of a running system" use-case, it would actually make more sense to snapshot a visible subvol to a non-mounted location, rather than the other way around.

The other thing that would be useful, if you're going to allow FS operations on non-mounted objects, is then to delete a subvolume by ID.

Quoted 162 lines

Signed-off-by Jeff Mahoney <[email protected]> --- cmds-subvolume.c

| 105 +++++++++++++++++++++++++++++++++++++++++--------------
ioctl.h | 6 ++- man/btrfs.8.in | 31
++++++++++++++-- 3 files changed, 112 insertions(+), 30 deletions(-)

--- a/cmds-subvolume.c +++ b/cmds-subvolume.c @@ -14,6 +14,7 @@ * Boston, MA 021110-1307, USA. */

+#define _GNU_SOURCE #include <stdio.h> #include <stdlib.h> #include <string.h> @@ -576,6 +577,7 @@ out: static const char * const cmd_snapshot_usage[] = { "btrfs subvolume snapshot [-r] <source> <dest>|[<dest>/]<name>", "btrfs subvolume snapshot [-r]
[-i <qgroupid>] <source> <dest>|[<dest>/]<name>", + "btrfs
subvolume snapshot [-r] [-i <qgroupid>] -s <subvolid> <dest>/<name>", "Create a snapshot of the subvolume", "Create a writable/readonly snapshot of the subvolume <source> with", "the name <name> in the <dest> directory. If only <dest> is given,",

(quoted diff) +0 -0

@@ -584,12 +586,27 @@ static const char * const cmd_snapshot_u 

"-r create a readonly snapshot", "-i <qgroupid> add
the newly created snapshot to a qgroup. This", "
option can be given multiple times.", + "-s <subvolid> create a
snapshot using the subvolume id. This", + " is
useful for snapshotting subvolumes outside", + " of
the mounted namespace.", NULL };

+static int get_subvolid(const char *str, u64 *subvolid) +{ +
char *p; + errno = 0; + *subvolid = strtoull(optarg, &p, 10); +
if (errno || *p != '\0') { + fprintf(stderr, "ERROR: invalid
subvolume id '%s'\n", optarg); + return -EINVAL; + } + return
0; +} + static int cmd_snapshot(int argc, char **argv) { - char
*subvol, *dst; + char *subvol = NULL, *dst; int res, retval; int
fd = -1, fddst = -1; int len, readonly = 0; @@ -597,6 +614,9 @@
static int cmd_snapshot(int argc, char * char *dupdir = NULL;
char *newname; char *dstdir; + u64 subvolid = 0; + char
*subvol_descr = NULL; + int nargs = 2; struct
btrfs_ioctl_vol_args_v2 args; struct btrfs_qgroup_inherit
*inherit = NULL; DIR *dirstream1 = NULL, *dirstream2 = NULL; @@ -604,7 +624,7 @@ static int cmd_snapshot(int argc, char * optind
= 1; memset(&args, 0, sizeof(args)); while (1) { - int c =
getopt(argc, argv, "c:i:r"); + int c = getopt(argc, argv,
"c:i:rs:"); if (c < 0) break;

(quoted diff) +0 -0

@@ -633,27 +653,39 @@ static int cmd_snapshot(int argc, char * 
 goto out; } break; +		case 's': +			res = get_subvolid(optarg,

&subvolid); + if (res) { + retval = res; + goto out; +
} + nargs = 1; + break; default: usage(cmd_snapshot_usage);
} }

(quoted diff) +0 -1

-	if (check_argc_exact(argc - optind, 2)) +	if

(check_argc_exact(argc - optind, nargs))
usage(cmd_snapshot_usage);

(quoted diff) +0 -1

-	subvol = argv[optind]; -	dst = argv[optind + 1]; +	if (nargs ==

2) { + subvol = argv[optind]; + dst = argv[optind + 1];

(quoted diff) +0 -1

-	retval = 1;	/* failure */ -	res = test_issubvolume(subvol); -

if (res < 0) { - fprintf(stderr, "ERROR: error accessing
'%s'\n", subvol); - goto out; - } - if (!res) { -
fprintf(stderr, "ERROR: '%s' is not a subvolume\n", subvol); -
goto out; - } + retval = 1; /* failure */ + res =
test_issubvolume(subvol); + if (res < 0) { + fprintf(stderr,
"ERROR: error accessing '%s'\n", subvol); + goto out; + } +
if (!res) { + fprintf(stderr, "ERROR: '%s' is not a
subvolume\n", + subvol); + goto out; + } + } else + dst =
argv[optind];

res = test_isdir(dst); if (res == 0) { @@ -662,6 +694,13 @@ static int cmd_snapshot(int argc, char * }

if (res > 0) { + if (!subvol) { + retval = 1; +
fprintf(stderr, + "ERROR: '%s' exists and must not when
snapshotting by specifying subvolid.\n", + dst); + goto
out; + } dupname = strdup(subvol); newname = basename(dupname);
dstdir = dst; @@ -692,22 +731,34 @@ static int cmd_snapshot(int argc, char * goto out; }

(quoted diff) +0 -1

-	fd = open_file_or_dir(subvol, &dirstream2); -	if (fd < 0) { -

fprintf(stderr, "ERROR: can't access '%s'\n", dstdir); + if
(subvol) { + fd = open_file_or_dir(subvol, &dirstream2); + if
(fd < 0) { + fprintf(stderr, "ERROR: can't access '%s'\n",
dstdir); + goto out; + } + args.fd = fd; + res =
asprintf(&subvol_descr, "'%s'", subvol); + } else { +
args.subvolid = subvolid; + args.flags |=
BTRFS_SUBVOL_CREATE_SUBVOLID; + res = asprintf(&subvol_descr,
"subvolume id %llu", subvolid); + } + if (res < 0) { +
fprintf(stderr, "ERROR: can't allocate memory\n"); + retval =
1; goto out; }

if (readonly) { args.flags |= BTRFS_SUBVOL_RDONLY; - printf("Create a readonly snapshot of '%s' in '%s/%s'\n", -
subvol, dstdir, newname); + printf("Create a readonly snapshot
of %s in '%s/%s'\n", + subvol_descr, dstdir, newname); }
else { - printf("Create a snapshot of '%s' in '%s/%s'\n", -
subvol, dstdir, newname); + printf("Create a snapshot of %s in
'%s/%s'\n", + subvol_descr, dstdir, newname); }

(quoted diff) +0 -1

-	args.fd = fd; if (inherit) { args.flags |=

BTRFS_SUBVOL_QGROUP_INHERIT; args.size = qgroup_inherit_size(inherit); @@ -718,8 +769,8 @@ static int cmd_snapshot(int argc, char * res = ioctl(fddst, BTRFS_IOC_SNAP_CREATE_V2, &args);

if (res < 0) { - fprintf( stderr, "ERROR: cannot snapshot '%s' -
%s\n", - subvol, strerror(errno)); + fprintf( stderr, "ERROR:
cannot snapshot %s - %s\n", + subvol_descr, strerror(errno));
goto out; }

(quoted diff) +0 -0

@@ -727,7 +778,9 @@ static int cmd_snapshot(int argc, char *
 

out: close_file_or_dir(fddst, dirstream1); -
close_file_or_dir(fd, dirstream2); + if (subvol) +
close_file_or_dir(fd, dirstream2); + free(subvol_descr);
free(inherit); free(dupname); free(dupdir); --- a/ioctl.h +++ b/ioctl.h @@ -41,6 +41,7 @@ struct btrfs_ioctl_vol_args { #define
BTRFS_SUBVOL_CREATE_ASYNC (1ULL << 0) #define BTRFS_SUBVOL_RDONLY
(1ULL << 1) #define BTRFS_SUBVOL_QGROUP_INHERIT (1ULL << 2)
+#define BTRFS_SUBVOL_CREATE_SUBVOLID (1ULL << 3)

#define BTRFS_QGROUP_INHERIT_SET_LIMITS (1ULL << 0)

(quoted diff) +0 -0

@@ -69,7 +70,10 @@ struct btrfs_ioctl_qgroup_limit_args { #define

BTRFS_SUBVOL_NAME_MAX 4039

struct btrfs_ioctl_vol_args_v2 { - __s64 fd; + union { + __s64
fd; + __u64 subvolid; + }; __u64 transid; __u64 flags; union {
--- a/man/btrfs.8.in +++ b/man/btrfs.8.in @@ -12,7 +12,9 @@ btrfs \- control a btrfs filesystem .PP \fBbtrfs\fP \fBsubvolume list\fP [\fIoptions\fP] [-G [+|-]\fIvalue\fP] [-C [+|-]\fIvalue\fP] [--sort=rootid,gen,ogen,path] \fI<path>\fP .PP -\fBbtrfs\fP \fBsubvolume snapshot\fP [-r] \fI<source>\fP \fI<dest>\fP|[\fI<dest>\fP/]\fI<name>\fP +\fBbtrfs\fP \fBsubvolume snapshot\fP [-r] [-i qgroupid] \fI<source>\fP \fI<dest>\fP|[\fI<dest>\fP/]\fI<name>\fP +.PP +\fBbtrfs\fP \fBsubvolume snapshot\fP [-r] [-i qgroupid] \fI-s <subvolid>\fP \fI<dest>/<name>\fP .PP \fBbtrfs\fP \fBsubvolume get-default\fP\fI <path>\fP .PP @@ -242,12 +244,35 @@ for \fB--sort\fP you can combine some it .RE .TP

-\fBsubvolume snapshot\fP [-r] \fI<source>\fP \fI<dest>\fP|[\fI<dest>\fP/]\fI<name>\fP +\fBsubvolume snapshot\fP [-r] [-i qgroupid] \fI<source>\fP \fI<dest>\fP|[\fI<dest>\fP/]\fI<name>\fP Create a writable/readonly snapshot of the subvolume \fI<source>\fR with the name \fI<name>\fR in the \fI<dest>\fR directory. If only \fI<dest>\fR is given, the subvolume will be named the basename of \fI<source>\fR. If \fI<source>\fR is not a subvolume, \fBbtrfs\fR returns an error. -If \fI-r\fR is given, the snapshot will be readonly. +.RS + +\fIOptions\fP +.IP \fB-r\fP 5 +The newly created snapshot will be readonly. +.IP "\fB-i\fP \fI<qgroupid>\fR" 5 +Add the newly created subvolume to a qgroup. This option can be given multiple +times. +.RE +.TP + +\fBsubvolume snapshot\fP [-r] [-i qgroupid] \fI-s <subvolid>\fP \fI<dest>\fP/\fI<name>\fP +Create a writable/readonly snapshot of the subvolume \fI<subvolid>\fR with the +name \fI<name>\fR in the \fI<dest>\fR directory. +If \fI<subvolid>\fR does not refer to a subvolume, \fBbtrfs\fR returns an error. +.RS + +\fIOptions\fP +.IP \fB-r\fP 5 +The newly created snapshot will be readonly. +.IP "\fB-i\fP \fI<qgroupid>\fR" 5 +Add the newly created subvolume to a qgroup. This option can be given multiple +times. +.RE .TP

Quoted 1 line

\fBsubvolume get-default\fR\fI <path>\fR