mkfs.btrfs: allow UUID specification at mkfs time

Allow the specification of the filesystem UUID at mkfs time.

(Implemented only for mkfs.btrfs, not btrfs-convert).

Signed-off-by Eric Sandeen <[email protected]>

---

btrfs-convert.c +1 -1

index a8b2c51..d62d4f8 100644
@@ -2240,7 +2240,7 @@ static int do_convert(const char *devname, int datacsum, int packing,
  		goto fail;
  	}
  	ret = make_btrfs(fd, devname, ext2_fs->super->s_volume_name,
-			 blocks, total_bytes, blocksize, blocksize,
+			 NULL, blocks, total_bytes, blocksize, blocksize,
  			 blocksize, blocksize, 0);
  	if (ret) {
  		fprintf(stderr, "unable to create initial ctree: %s\n",

man/mkfs.btrfs.8.in +4 -0

index bef509d..4450d03 100644
@@ -16,6 +16,7 @@ mkfs.btrfs \- create a btrfs filesystem
  [ \fB\-r\fP\fI rootdir\fP ]
  [ \fB\-K\fP ]
  [ \fB\-O\fP\fI feature1,feature2,...\fP ]
+[ \fB\-U\fP\fI uuid\fP ]
  [ \fB\-h\fP ]
  [ \fB\-V\fP ]
  \fI device\fP [ \fIdevice ...\fP ]

@@ -90,6 +91,9 @@ To see all run
 
  \fBmkfs.btrfs -O list-all\fR
  .TP
+\fB\-U\fR, \fB\-\-uuid \fR
+Create the filesystem with the specified UUID.
+.TP
  \fB\-V\fR, \fB\-\-version\fR
  Print the \fBmkfs.btrfs\fP version and exit.
  .SH UNIT

mkfs.c +8 -2

index dbd83f5..eccb08f 100644
@@ -288,6 +288,7 @@ static void print_usage(void)
  	fprintf(stderr, "\t -r --rootdir the source directory\n");
  	fprintf(stderr, "\t -K --nodiscard do not perform whole device TRIM\n");
  	fprintf(stderr, "\t -O --features comma separated list of filesystem features\n");
+	fprintf(stderr, "\t -U --uuid specify the filesystem UUID\n");
  	fprintf(stderr, "\t -V --version print the mkfs.btrfs version and exit\n");
  	fprintf(stderr, "%s\n", BTRFS_BUILD_VERSION);
  	exit(1);

@@ -351,6 +352,7 @@ static struct option long_options[] = {
  	{ "rootdir", 1, NULL, 'r' },
  	{ "nodiscard", 0, NULL, 'K' },
  	{ "features", 0, NULL, 'O' },
+	{ "uuid", 0, NULL, 'U' },
  	{ NULL, 0, NULL, 0}
  };
 

@@ -1273,11 +1275,12 @@ int main(int ac, char **av)
  	int dev_cnt = 0;
  	int saved_optind;
  	char estr[100];
+	char *fs_uuid = NULL;
  	u64 features = DEFAULT_MKFS_FEATURES;
 
  	while(1) {
  		int c;
-		c = getopt_long(ac, av, "A:b:fl:n:s:m:d:L:O:r:VMK",
+		c = getopt_long(ac, av, "A:b:fl:n:s:m:d:L:O:r:U:VMK",
  				long_options, &option_index);
  		if (c < 0)
  			break;

@@ -1346,6 +1349,9 @@ int main(int ac, char **av)
  				source_dir = optarg;
  				source_dir_set = 1;
  				break;
+			case 'U':
+				fs_uuid = optarg;
+				break;
  			case 'K':
  				discard = 0;
  				break;

@@ -1514,7 +1520,7 @@ int main(int ac, char **av)
 
  	process_fs_features(features);
 
-	ret = make_btrfs(fd, file, label, blocks, dev_block_count,
+	ret = make_btrfs(fd, file, label, fs_uuid, blocks, dev_block_count,
  			 nodesize, leafsize,
  			 sectorsize, stripesize, features);
  	if (ret) {

utils.c +10 -3

index 3e9c527..3f46e8f 100644
@@ -93,12 +93,12 @@ static u64 reference_root_table[] = {
  	[6] =	BTRFS_CSUM_TREE_OBJECTID,
  };
 
-int make_btrfs(int fd, const char *device, const char *label,
+int make_btrfs(int fd, const char *device, const char *label, char *fs_uuid,
  	       u64 blocks[7], u64 num_bytes, u32 nodesize,
  	       u32 leafsize, u32 sectorsize, u32 stripesize, u64 features)
  {
  	struct btrfs_super_block super;
-	struct extent_buffer *buf;
+	struct extent_buffer *buf = NULL;
  	struct btrfs_root_item root_item;
  	struct btrfs_disk_key disk_key;
  	struct btrfs_extent_item *extent_item;

@@ -125,7 +125,14 @@ int make_btrfs(int fd, const char *device, const char *label,
  	memset(&super, 0, sizeof(super));
 
  	num_bytes = (num_bytes / sectorsize) * sectorsize;
-	uuid_generate(super.fsid);
+	if (fs_uuid) {
+		if (uuid_parse(fs_uuid, super.fsid) != 0) {
+			fprintf(stderr, "could not parse UUID: %s\n", fs_uuid);
+			ret = -EINVAL;
+			goto out;
+		}
+	} else
+		uuid_generate(super.fsid);
  	uuid_generate(super.dev_item.uuid);
  	uuid_generate(chunk_tree_uuid);
 

utils.h +1 -2

index 3c62066..054cbb6 100644
@@ -40,7 +40,7 @@
  #define BTRFS_UUID_UNPARSED_SIZE	37
 
  int make_btrfs(int fd, const char *device, const char *label,
-	       u64 blocks[6], u64 num_bytes, u32 nodesize,
+	       char *fs_uuid, u64 blocks[6], u64 num_bytes, u32 nodesize,
  	       u32 leafsize, u32 sectorsize, u32 stripesize, u64 features);
  int btrfs_make_root_dir(struct btrfs_trans_handle *trans,
  			struct btrfs_root *root, u64 objectid);
 
 
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Quoted 3 lines · Eric Sandeen

Allow the specification of the filesystem UUID at mkfs time.

(Implemented only for mkfs.btrfs, not btrfs-convert).

Just out of curiosity, this option is used for what kind of use case? I notice Ext4 also has this option.:-)

Quoted 3 lines · Eric Sandeen

Allow the specification of the filesystem UUID at mkfs time.

(Implemented only for mkfs.btrfs, not btrfs-convert).

Just out of curiosity, this option is used for what kind of use case? I notice Ext4 also has this option.:-)

Quoted 139 lines

Signed-off-by Eric Sandeen <[email protected]>

---

btrfs-convert.c +1 -1

index a8b2c51..d62d4f8 100644
@@ -2240,7 +2240,7 @@ static int do_convert(const char *devname, int datacsum, int packing,
          goto fail;
      }
      ret = make_btrfs(fd, devname, ext2_fs->super->s_volume_name,
-             blocks, total_bytes, blocksize, blocksize,
+             NULL, blocks, total_bytes, blocksize, blocksize,
               blocksize, blocksize, 0);
      if (ret) {
          fprintf(stderr, "unable to create initial ctree: %s\n",

man/mkfs.btrfs.8.in +4 -0

index bef509d..4450d03 100644
@@ -16,6 +16,7 @@ mkfs.btrfs \- create a btrfs filesystem
  [ \fB\-r\fP\fI rootdir\fP ]
  [ \fB\-K\fP ]
  [ \fB\-O\fP\fI feature1,feature2,...\fP ]
+[ \fB\-U\fP\fI uuid\fP ]
  [ \fB\-h\fP ]
  [ \fB\-V\fP ]
  \fI device\fP [ \fIdevice ...\fP ]

@@ -90,6 +91,9 @@ To see all run
    \fBmkfs.btrfs -O list-all\fR
  .TP
+\fB\-U\fR, \fB\-\-uuid \fR
+Create the filesystem with the specified UUID.
+.TP
  \fB\-V\fR, \fB\-\-version\fR
  Print the \fBmkfs.btrfs\fP version and exit.
  .SH UNIT

mkfs.c +2 -0

index dbd83f5..eccb08f 100644
@@ -288,6 +288,7 @@ static void print_usage(void)
      fprintf(stderr, "\t -r --rootdir the source directory\n");
      fprintf(stderr, "\t -K --nodiscard do not perform whole device TRIM\n");
      fprintf(stderr, "\t -O --features comma separated list of filesystem features\n");
+    fprintf(stderr, "\t -U --uuid specify the filesystem UUID\n");
      fprintf(stderr, "\t -V --version print the mkfs.btrfs version and exit\n");
      fprintf(stderr, "%s\n", BTRFS_BUILD_VERSION);
      exit(1);

@@ -351,6 +352,7 @@ static struct option long_options[] = {
      { "rootdir", 1, NULL, 'r' },
      { "nodiscard", 0, NULL, 'K' },
      { "features", 0, NULL, 'O' },
+    { "uuid", 0, NULL, 'U' },
      { NULL, 0, NULL, 0}
  };
  @@ -1273,11 +1275,12 @@ int main(int ac, char **av)

      int dev_cnt = 0;
      int saved_optind;
      char estr[100];

mkfs.c +6 -1

+    char *fs_uuid = NULL;
      u64 features = DEFAULT_MKFS_FEATURES;
        while(1) {
          int c;
-        c = getopt_long(ac, av, "A:b:fl:n:s:m:d:L:O:r:VMK",
+        c = getopt_long(ac, av, "A:b:fl:n:s:m:d:L:O:r:U:VMK",
                  long_options, &option_index);
          if (c < 0)
              break;

@@ -1346,6 +1349,9 @@ int main(int ac, char **av)
                  source_dir = optarg;
                  source_dir_set = 1;
                  break;
+            case 'U':
+                fs_uuid = optarg;
+                break;
              case 'K':
                  discard = 0;
                  break;

@@ -1514,7 +1520,7 @@ int main(int ac, char **av)
        process_fs_features(features);
  -    ret = make_btrfs(fd, file, label, blocks, dev_block_count,
+    ret = make_btrfs(fd, file, label, fs_uuid, blocks, dev_block_count,
               nodesize, leafsize,
               sectorsize, stripesize, features);
      if (ret) {

utils.c +10 -2

index 3e9c527..3f46e8f 100644
@@ -93,12 +93,12 @@ static u64 reference_root_table[] = {
      [6] =    BTRFS_CSUM_TREE_OBJECTID,
  };
  -int make_btrfs(int fd, const char *device, const char *label,
+int make_btrfs(int fd, const char *device, const char *label, char *fs_uuid,
             u64 blocks[7], u64 num_bytes, u32 nodesize,
             u32 leafsize, u32 sectorsize, u32 stripesize, u64 features)
  {
      struct btrfs_super_block super;
-    struct extent_buffer *buf;
+    struct extent_buffer *buf = NULL;
      struct btrfs_root_item root_item;
      struct btrfs_disk_key disk_key;
      struct btrfs_extent_item *extent_item;

@@ -125,7 +125,14 @@ int make_btrfs(int fd, const char *device, const char *label,
      memset(&super, 0, sizeof(super));
        num_bytes = (num_bytes / sectorsize) * sectorsize;
-    uuid_generate(super.fsid);
+    if (fs_uuid) {
+        if (uuid_parse(fs_uuid, super.fsid) != 0) {
+            fprintf(stderr, "could not parse UUID: %s\n", fs_uuid);
+            ret = -EINVAL;
+            goto out;
+        }
+    } else
+        uuid_generate(super.fsid);
      uuid_generate(super.dev_item.uuid);
      uuid_generate(chunk_tree_uuid);
  diff --git a/utils.h b/utils.h

index 3c62066..054cbb6 100644

utils.h +1 -1

@@ -40,7 +40,7 @@
  #define BTRFS_UUID_UNPARSED_SIZE    37
    int make_btrfs(int fd, const char *device, const char *label,
-           u64 blocks[6], u64 num_bytes, u32 nodesize,
+           char *fs_uuid, u64 blocks[6], u64 num_bytes, u32 nodesize,
             u32 leafsize, u32 sectorsize, u32 stripesize, u64 features);
  int btrfs_make_root_dir(struct btrfs_trans_handle *trans,
              struct btrfs_root *root, u64 objectid);
 

Signature · 5 lines

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Quoted 3 lines · Eric Sandeen

Allow the specification of the filesystem UUID at mkfs time.

(Implemented only for mkfs.btrfs, not btrfs-convert).

Just out of curiosity, this option is used for what kind of use case? I notice Ext4 also has this option.:-)

Quoted 6 lines · Eric Sandeen

Quoted 3 lines

Allow the specification of the filesystem UUID at mkfs time.

(Implemented only for mkfs.btrfs, not btrfs-convert).

Just out of curiosity, this option is used for what kind of use case? I notice Ext4 also has this option.:-)

Personally I can't think of any "average" or "normal" use case. The simplest case however is in using predictable/predetermined UUIDs.

Allow the specification of the filesystem UUID at mkfs time.

Hi Eric,

Quoted 1 line · Eric Sandeen

Allow the specification of the filesystem UUID at mkfs time.

I suggest to add some warning when this options is used, because the behavior could be very different than the one expected.

I suspect that BTRFS tracks the filesystem by UUID and not by devices. When two filesystems have the same UUID at the same time, it may mount the wrong one.

$ #
$ # Make two *different* filesystems with the *same* UUID
$ #
$ UUID=e285c9bd-ea97-40b3-ad7d-8713dcfd5eea
$ sudo ./mkfs.btrfs -f -U $UUID /dev/vdg
$ sudo ./mkfs.btrfs -f -U $UUID /dev/vdh

$ #
$ # from the beginning "btrfs fi show" reports wrong information
$ #
$ sudo btrfs fi show
Label: none  uuid: e285c9bd-ea97-40b3-ad7d-8713dcfd5eea
	Total devices 1 FS bytes used 96.00KB
	devid    1 size 50.00GB used 4.00MB path /dev/vdh
	devid    1 size 50.00GB used 2.04GB path /dev/vdg

$ #
$ # mount the first one, create a new file then un-mount it
$ #
$ sudo mount /dev/vdg /mnt/btrfs1
$ sudo touch /mnt/btrfs1/dev-vdg
$ sudo umount /dev/vdg

$ #
$ # mount the second one, it should be empty
$ # instead btrfs mount the first one
$ #
$ sudo mount /dev/vdh /mnt/btrfs2
$ ls -l /mnt/btrfs2
total 0
-rw-r--r-- 1 root root 0 May 14 16:12 dev-vdg

I am not against this option; I am suggesting to add a explicit warning to the user about the risk of doing that, both on the man pages and into the program. The warning should say that this option is only for testing. Better ask for a confirmation (even with an undocumented switch like '--I-know-that-I-am-doing-something-really-dangerous').

For the record, BTRFS seems unable to mount at the same time two different filesystems with the same UUID:

$ #
$ # try to mount two fs with the same UUID, but BTRFS doesn't allow it
$ #
$ sudo mount /dev/vdh /mnt/btrfs2
$ sudo mount /dev/vdg /mnt/btrfs1
ERROR: mount failed : 16 - Device or resource busy

BR
G.Baroncelli

Quoted 3 lines · Wang Shilong

Quoted 2 lines · Eric Sandeen

Allow the specification of the filesystem UUID at mkfs time.

Quoted 3 lines

Quoted 1 line

(Implemented only for mkfs.btrfs, not btrfs-convert).

Just out of curiosity, this option is used for what kind of use case? I notice Ext4 also has this option.:-)

Personally I can't think of any "average" or "normal" use case. The simplest case however is in using predictable/predetermined UUIDs.

Certain things, such as testing or perhaps even large-scale automation, are likely simpler to implement with a predictable UUID.

Hi Eric,

Quoted 1 line · Eric Sandeen

Allow the specification of the filesystem UUID at mkfs time.

I suggest to add some warning when this options is used, because the behavior could be very different than the one expected.

I suspect that BTRFS tracks the filesystem by UUID and not by devices. When two filesystems have the same UUID at the same time, it may mount the wrong one.

$ #
$ # Make two *different* filesystems with the *same* UUID
$ #
$ UUID=e285c9bd-ea97-40b3-ad7d-8713dcfd5eea
$ sudo ./mkfs.btrfs -f -U $UUID /dev/vdg
$ sudo ./mkfs.btrfs -f -U $UUID /dev/vdh

$ #
$ # from the beginning "btrfs fi show" reports wrong information
$ #
$ sudo btrfs fi show
Label: none  uuid: e285c9bd-ea97-40b3-ad7d-8713dcfd5eea
	Total devices 1 FS bytes used 96.00KB
	devid    1 size 50.00GB used 4.00MB path /dev/vdh
	devid    1 size 50.00GB used 2.04GB path /dev/vdg

$ #
$ # mount the first one, create a new file then un-mount it
$ #
$ sudo mount /dev/vdg /mnt/btrfs1
$ sudo touch /mnt/btrfs1/dev-vdg
$ sudo umount /dev/vdg

$ #
$ # mount the second one, it should be empty
$ # instead btrfs mount the first one
$ #
$ sudo mount /dev/vdh /mnt/btrfs2
$ ls -l /mnt/btrfs2
total 0
-rw-r--r-- 1 root root 0 May 14 16:12 dev-vdg

I am not against this option; I am suggesting to add a explicit warning to the user about the risk of doing that, both on the man pages and into the program. The warning should say that this option is only for testing. Better ask for a confirmation (even with an undocumented switch like '--I-know-that-I-am-doing-something-really-dangerous').

For the record, BTRFS seems unable to mount at the same time two different filesystems with the same UUID:

$ #
$ # try to mount two fs with the same UUID, but BTRFS doesn't allow it
$ #
$ sudo mount /dev/vdh /mnt/btrfs2
$ sudo mount /dev/vdg /mnt/btrfs1
ERROR: mount failed : 16 - Device or resource busy

BR
G.Baroncelli

Quoted 6 lines

I am not against this option; I am suggesting to add a explicit warning to the user about the risk of doing that, both on the man pages and into the program. The warning should say that this option is only for testing. Better ask for a confirmation (even with an undocumented switch like '--I-know-that-I-am-doing-something-really-dangerous').

meh. ext4 and xfs have had the ability to either set or change the UUID for years, and I've not heard of any horror stories.

Quoted 4 lines

For the record, BTRFS seems unable to mount at the same time two different filesystems with the same UUID:

Quoted 6 lines

$ #
$ # try to mount two fs with the same UUID, but BTRFS doesn't allow it
$ #
$ sudo mount /dev/vdh /mnt/btrfs2
$ sudo mount /dev/vdg /mnt/btrfs1
ERROR: mount failed : 16 - Device or resource busy

(presumably the kernel said something, too?)

and this seems to make it even more safe.

-Eric

Quoted 4 lines

BR
G.Baroncelli

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Quoted 6 lines

I am not against this option; I am suggesting to add a explicit warning to the user about the risk of doing that, both on the man pages and into the program. The warning should say that this option is only for testing. Better ask for a confirmation (even with an undocumented switch like '--I-know-that-I-am-doing-something-really-dangerous').

meh. ext4 and xfs have had the ability to either set or change the UUID for years, and I've not heard of any horror stories.

utils.c +8 -0

+		}
+		if (!test_uuid_unique(fs_uuid)) {
+			fprintf(stderr, "non-unique UUID: %s\n", fs_uuid);
+			ret = -EBUSY;
+			goto out;
+		}
+	} else
+		uuid_generate(super.fsid);
 	uuid_generate(super.dev_item.uuid);
 	uuid_generate(chunk_tree_uuid);

Thanks for adding the uuid uniqueness check, that was my major objection for previous patch iterations,

http://www.spinics.net/lists/linux-btrfs/msg30572.html

we can now use it for convert as well (to generate or copy the uuid).

utils.c int make_btrfs(int fd, const char *device, const char *label, · line 161

Quoted 10 lines

utils.c +5 -1

@@ -125,7 +154,19 @@ int make_btrfs(int fd, const char *device, const char *label,
 	memset(&super, 0, sizeof(super));
 
 	num_bytes = (num_bytes / sectorsize) * sectorsize;
-	uuid_generate(super.fsid);
+	if (fs_uuid) {
+		if (uuid_parse(fs_uuid, super.fsid) != 0) {
+			fprintf(stderr, "could not parse UUID: %s\n", fs_uuid);
+			ret = -EINVAL;
+			goto out;

I think the uuid validity check comes too late, IMHO it should be done after the while/getopt block outside of make_btrfs. At this point eg. the discard or device zeroing is already done.

I would not mind to keep the check here as well as a last sanity check, though the number of mkfs_btrfs callers is 1 and the function is not exported to the library.

Quoted 10 lines

utils.c +8 -0

+		}
+		if (!test_uuid_unique(fs_uuid)) {
+			fprintf(stderr, "non-unique UUID: %s\n", fs_uuid);
+			ret = -EBUSY;
+			goto out;
+		}
+	} else
+		uuid_generate(super.fsid);
 	uuid_generate(super.dev_item.uuid);
 	uuid_generate(chunk_tree_uuid);

Quoted 3 lines · Eric Sandeen

Quoted 3 lines

utils.c +0 -0

@@ -125,7 +154,19 @@ int make_btrfs(int fd, const char *device, const char *label,
 	memset(&super, 0, sizeof(super));
 

Quoted 7 lines

utils.c int make_btrfs(int fd, const char *device, const char *label, · line 161

Quoted 7 lines

utils.c +5 -1

 	num_bytes = (num_bytes / sectorsize) * sectorsize;
-	uuid_generate(super.fsid);
+	if (fs_uuid) {
+		if (uuid_parse(fs_uuid, super.fsid) != 0) {
+			fprintf(stderr, "could not parse UUID: %s\n", fs_uuid);
+			ret = -EINVAL;
+			goto out;

I think the uuid validity check comes too late, IMHO it should be done after the while/getopt block outside of make_btrfs. At this point eg. the discard or device zeroing is already done.

Allow the specification of the filesystem UUID at mkfs time.

Non-unique unique IDs are rejected. This includes attempting to re-mkfs with the same UUID; if you really want to do that, you can mkfs with a new UUID, then re-mkfs with the one you wanted. ;)

(Implemented only for mkfs.btrfs, not btrfs-convert).

Signed-off-by Eric Sandeen <[email protected]>

---

NB: the prior patch didn't work well if you re-mkfs'd with the same UUID; to be honest I didn't get to the bottom of it, but the fact that that old UUID was already in an internal list of present devices seems to have confused things.

V2: reject non-unique unique IDs.
V3: test for non-unique unique IDs early in mkfs.

btrfs-convert.c +1 -1

index a8b2c51..d62d4f8 100644
@@ -2240,7 +2240,7 @@ static int do_convert(const char *devname, int datacsum, int packing,
 		goto fail;
 	}
 	ret = make_btrfs(fd, devname, ext2_fs->super->s_volume_name,
-			 blocks, total_bytes, blocksize, blocksize,
+			 NULL, blocks, total_bytes, blocksize, blocksize,
 			 blocksize, blocksize, 0);
 	if (ret) {
 		fprintf(stderr, "unable to create initial ctree: %s\n",

man/mkfs.btrfs.8.in +4 -0

index bef509d..4450d03 100644
@@ -16,6 +16,7 @@ mkfs.btrfs \- create a btrfs filesystem
 [ \fB\-r\fP\fI rootdir\fP ]
 [ \fB\-K\fP ]
 [ \fB\-O\fP\fI feature1,feature2,...\fP ]
+[ \fB\-U\fP\fI uuid\fP ]
 [ \fB\-h\fP ]
 [ \fB\-V\fP ]
 \fI device\fP [ \fIdevice ...\fP ]

@@ -90,6 +91,9 @@ To see all run
 
 \fBmkfs.btrfs -O list-all\fR
 .TP
+\fB\-U\fR, \fB\-\-uuid \fR
+Create the filesystem with the specified UUID, which must not already exist on the system.
+.TP
 \fB\-V\fR, \fB\-\-version\fR
 Print the \fBmkfs.btrfs\fP version and exit.
 .SH UNIT

mkfs.c +9 -1

index dbd83f5..d67a5ba 100644
@@ -288,6 +288,7 @@ static void print_usage(void)
 	fprintf(stderr, "\t -r --rootdir the source directory\n");
 	fprintf(stderr, "\t -K --nodiscard do not perform whole device TRIM\n");
 	fprintf(stderr, "\t -O --features comma separated list of filesystem features\n");
+	fprintf(stderr, "\t -U --uuid specify the filesystem UUID\n");
 	fprintf(stderr, "\t -V --version print the mkfs.btrfs version and exit\n");
 	fprintf(stderr, "%s\n", BTRFS_BUILD_VERSION);
 	exit(1);

@@ -351,6 +352,7 @@ static struct option long_options[] = {
 	{ "rootdir", 1, NULL, 'r' },
 	{ "nodiscard", 0, NULL, 'K' },
 	{ "features", 0, NULL, 'O' },
+	{ "uuid", 0, NULL, 'U' },
 	{ NULL, 0, NULL, 0}
 };
 

@@ -1273,11 +1275,12 @@ int main(int ac, char **av)
 	int dev_cnt = 0;
 	int saved_optind;
 	char estr[100];
+	char *fs_uuid = NULL;
 	u64 features = DEFAULT_MKFS_FEATURES;
 
 	while(1) {
 		int c;
-		c = getopt_long(ac, av, "A:b:fl:n:s:m:d:L:O:r:VMK",
+		c = getopt_long(ac, av, "A:b:fl:n:s:m:d:L:O:r:U:VMK",
 				long_options, &option_index);
 		if (c < 0)
 			break;

@@ -1346,6 +1349,9 @@ int main(int ac, char **av)
 				source_dir = optarg;
 				source_dir_set = 1;
 				break;
+			case 'U':
+				fs_uuid = optarg;
+				break;
 			case 'K':
 				discard = 0;
 				break;

@@ -1368,6 +1374,20 @@ int main(int ac, char **av)
 			"The -r option is limited to a single device\n");
 		exit(1);
 	}
+
+	if (fs_uuid) {

mkfs.c +3 -1

+	}
+	
 	while (dev_cnt-- > 0) {
 		file = av[optind++];
 		if (is_block_device(file))

@@ -1514,7 +1534,7 @@ int main(int ac, char **av)
 
 	process_fs_features(features);
 
-	ret = make_btrfs(fd, file, label, blocks, dev_block_count,
+	ret = make_btrfs(fd, file, label, fs_uuid, blocks, dev_block_count,
 			 nodesize, leafsize,
 			 sectorsize, stripesize, features);
 	if (ret) {

utils.c +6 -1

index 3e9c527..cfac0d4 100644
@@ -93,12 +93,41 @@ static u64 reference_root_table[] = {
 	[6] =	BTRFS_CSUM_TREE_OBJECTID,
 };
 
-int make_btrfs(int fd, const char *device, const char *label,
+int test_uuid_unique(char *fs_uuid)
+{
+	int unique = 1;
+	blkid_dev_iterate iter = NULL;
+	blkid_dev dev = NULL;
+	blkid_cache cache = NULL;

utils.c +16 -2

+		dev = blkid_verify(cache, dev);
+		if (dev) {
+			unique = 0;
+			break;
+		}
+	}
+
+	blkid_dev_iterate_end(iter);
+	blkid_put_cache(cache);
+
+	return unique;
+}
+
+int make_btrfs(int fd, const char *device, const char *label, char *fs_uuid,
 	       u64 blocks[7], u64 num_bytes, u32 nodesize,
 	       u32 leafsize, u32 sectorsize, u32 stripesize, u64 features)
 {
 	struct btrfs_super_block super;
-	struct extent_buffer *buf;
+	struct extent_buffer *buf = NULL;
 	struct btrfs_root_item root_item;
 	struct btrfs_disk_key disk_key;
 	struct btrfs_extent_item *extent_item;

@@ -125,7 +154,20 @@ int make_btrfs(int fd, const char *device, const char *label,
 	memset(&super, 0, sizeof(super));
 
 	num_bytes = (num_bytes / sectorsize) * sectorsize;
-	uuid_generate(super.fsid);
+	if (fs_uuid) {

utils.c +3 -0

+	} else {
+		uuid_generate(super.fsid);
+	}
 	uuid_generate(super.dev_item.uuid);
 	uuid_generate(chunk_tree_uuid);
 

utils.h +2 -2

index 3c62066..4a404ae 100644
@@ -39,8 +39,9 @@
 
 #define BTRFS_UUID_UNPARSED_SIZE	37
 
+int test_uuid_unique(char *fs_uuid);
 int make_btrfs(int fd, const char *device, const char *label,
-	       u64 blocks[6], u64 num_bytes, u32 nodesize,
+	       char *fs_uuid, u64 blocks[6], u64 num_bytes, u32 nodesize,
 	       u32 leafsize, u32 sectorsize, u32 stripesize, u64 features);
 int btrfs_make_root_dir(struct btrfs_trans_handle *trans,
 			struct btrfs_root *root, u64 objectid);
 
--

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Quoted 20 lines · Eric Sandeen

Allow the specification of the filesystem UUID at mkfs time.

Non-unique unique IDs are rejected. This includes attempting to re-mkfs with the same UUID; if you really want to do that, you can mkfs with a new UUID, then re-mkfs with the one you wanted. ;)

(Implemented only for mkfs.btrfs, not btrfs-convert).

Signed-off-by Eric Sandeen <[email protected]>

---

NB: the prior patch didn't work well if you re-mkfs'd with the same UUID; to be honest I didn't get to the bottom of it, but the fact that that old UUID was already in an internal list of present devices seems to have confused things.

V2: reject non-unique unique IDs.
V3: test for non-unique unique IDs early in mkfs.

Quoted 10 lines

mkfs.c +6 -0

@@ -1368,6 +1374,20 @@ int main(int ac, char **av)
 			"The -r option is limited to a single device\n");
 		exit(1);
 	}
+
+	if (fs_uuid) {
+		uuid_t dummy_uuid;
+
+		if (uuid_parse(fs_uuid, dummy_uuid) != 0) {
+			fprintf(stderr, "could not parse UUID: %s\n", fs_uuid);

mkfs.c int main(int ac, char **av) · line 1388

Quoted 6 lines

mkfs.c +6 -0

+			exit(1);
+		}
+		if (!test_uuid_unique(fs_uuid)) {
+			fprintf(stderr, "non-unique UUID: %s\n", fs_uuid);
+			exit(1);
+		}

My test showed that this detect a false positive when the user tries to mkfs two time on the same device with the same uuid.

Quoted 19 lines

utils.c +10 -1

index 3e9c527..cfac0d4 100644
@@ -93,12 +93,41 @@ static u64 reference_root_table[] = {
 	[6] =	BTRFS_CSUM_TREE_OBJECTID,
 };
 
-int make_btrfs(int fd, const char *device, const char *label,
+int test_uuid_unique(char *fs_uuid)
+{
+	int unique = 1;
+	blkid_dev_iterate iter = NULL;
+	blkid_dev dev = NULL;
+	blkid_cache cache = NULL;
+
+	if (blkid_get_cache(&cache, 0) < 0) {
+		printf("ERROR: lblkid cache get failed\n");
+		return 1;

utils.c static u64 reference_root_table[] = { · line 111

Quoted 6 lines

utils.c +6 -0

+	}
+	blkid_probe_all(cache);
+	iter = blkid_dev_iterate_begin(cache);
+	blkid_dev_set_search(iter, "UUID", fs_uuid);
+
+	while (blkid_dev_next(iter, &dev) == 0) {

This function should skip the check for the devices involved in the mkfs.

Quoted 6 lines

utils.c +1 -1

@@ -125,7 +154,20 @@ int make_btrfs(int fd, const char *device, const char *label,
 	memset(&super, 0, sizeof(super));
 
 	num_bytes = (num_bytes / sectorsize) * sectorsize;
-	uuid_generate(super.fsid);
+	if (fs_uuid) {

utils.c int make_btrfs(int fd, const char *device, const char *label, · line 167

Quoted 10 lines

utils.c +10 -0

+		if (uuid_parse(fs_uuid, super.fsid) != 0) {
+			fprintf(stderr, "could not parse UUID: %s\n", fs_uuid);
+			ret = -EINVAL;
+			goto out;
+		}
+		if (!test_uuid_unique(fs_uuid)) {
+			fprintf(stderr, "non-unique UUID: %s\n", fs_uuid);
+			ret = -EBUSY;
+			goto out;
+		}

Why a second call to test_uuid_unique(fs_uuid) ?

Quoted 18 lines

Quoted 6 lines

utils.c +1 -1

@@ -125,7 +154,20 @@ int make_btrfs(int fd, const char *device, const char *label,
 	memset(&super, 0, sizeof(super));
 
 	num_bytes = (num_bytes / sectorsize) * sectorsize;
-	uuid_generate(super.fsid);
+	if (fs_uuid) {

utils.c int make_btrfs(int fd, const char *device, const char *label, · line 167

Quoted 10 lines

utils.c +10 -0

+		if (uuid_parse(fs_uuid, super.fsid) != 0) {
+			fprintf(stderr, "could not parse UUID: %s\n", fs_uuid);
+			ret = -EINVAL;
+			goto out;
+		}
+		if (!test_uuid_unique(fs_uuid)) {
+			fprintf(stderr, "non-unique UUID: %s\n", fs_uuid);
+			ret = -EBUSY;
+			goto out;
+		}

Why a second call to test_uuid_unique(fs_uuid) ?

Because kdave said he thought it was worth being paranoid in an earlier email, if I understood him correctly.

Quoted 19 lines · Eric Sandeen

Quoted 18 lines

Quoted 6 lines

utils.c +1 -1

@@ -125,7 +154,20 @@ int make_btrfs(int fd, const char *device, const char *label,
 	memset(&super, 0, sizeof(super));
 
 	num_bytes = (num_bytes / sectorsize) * sectorsize;
-	uuid_generate(super.fsid);
+	if (fs_uuid) {

utils.c int make_btrfs(int fd, const char *device, const char *label, · line 167

Quoted 10 lines

utils.c +10 -0

+		if (uuid_parse(fs_uuid, super.fsid) != 0) {
+			fprintf(stderr, "could not parse UUID: %s\n", fs_uuid);
+			ret = -EINVAL;
+			goto out;
+		}
+		if (!test_uuid_unique(fs_uuid)) {
+			fprintf(stderr, "non-unique UUID: %s\n", fs_uuid);
+			ret = -EBUSY;
+			goto out;
+		}

Why a second call to test_uuid_unique(fs_uuid) ?

Quoted 2 lines

Because kdave said he thought it was worth being paranoid in an earlier email, if I understood him correctly.

I'm thinking about it again. My original idea was not to easily allow to create a duplicate uuid to a regular user. But, if one uses --uuid already, that's something I can count as a willful action and any mistakes can be blamed on the user.

If we end up with a warning, then the documentation should say how spectacularly it can blow up the system.

So, in my testing, I found that re-mkfsing a device with the same UUID lead to weird & distant segfaults in other bits of code. Probably due to the uuid cache? </handwave> - I didn't dig into it, because ...

... people didn't want to be able to create duplicate UUIDs, so I figured the outright rejection of that was a trivial way to solve it ...

And like I mentioned, if you really want to recreate the same UUID, you can mkfs twice. It doesn't take long. ;)

I dunno, maybe that's too lame. For a feature that upstream development doesn't really seem to want, I'm not sure how much more effort I should put into it?