btrfs-progs: mkfs: add option to specify device uuid

Add option --device-uuid that will set the device uuid item in super
block.

This is useful for creating a filesystem with a specific device uuid,
namely for testing.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Documentation/mkfs.btrfs.rst

@@ -183,6 +183,12 @@ OPTIONS
         you can duplicate the UUID. However, for a multi-device filesystem, the UUID
         must not already exist on any currently present filesystem.
 
+--device-uuid <UUID>
+        Create the filesystem with the given device-uuid *UUID* (also known as
+        UUID_SUB in :command:`blkid`).  For a single device filesystem, you can
+        duplicate the device-uuid. However, used for a multi-device filesystem
+        this option will not work at the moment.
+
 -v|--verbose
         Increase verbosity level, default is 1.
 

mkfs/common.c

@@ -435,7 +435,12 @@ int make_btrfs(int fd, struct btrfs_mkfs_config *cfg)
 	} else {
 		uuid_parse(cfg->fs_uuid, super.fsid);
 	}
-	uuid_generate(super.dev_item.uuid);
+	if (!*cfg->dev_uuid) {
+		uuid_generate(super.dev_item.uuid);
+		uuid_unparse(super.dev_item.uuid, cfg->dev_uuid);
+	} else {
+		uuid_parse(cfg->dev_uuid, super.dev_item.uuid);
+	}
 	uuid_generate(chunk_tree_uuid);
 
 	for (i = 0; i < blocks_nr; i++) {

mkfs/common.h

@@ -90,7 +90,12 @@ struct btrfs_mkfs_config {
 
 	/* Logical addresses of superblock [0] and other tree roots */
 	u64 blocks[MKFS_BLOCK_COUNT + 1];
+
+	/* btrfs_super_block filesystem uuid */
 	char fs_uuid[BTRFS_UUID_UNPARSED_SIZE];
+
+	/* Set the given uuid to super block device_item. */
+	char dev_uuid[BTRFS_UUID_UNPARSED_SIZE];
 	char chunk_uuid[BTRFS_UUID_UNPARSED_SIZE];
 
 	/* Superblock offset after make_btrfs */

mkfs/main.c

@@ -431,6 +431,7 @@ static const char * const mkfs_usage[] = {
 	OPTLINE("-O|--features LIST", "comma separated list of filesystem features (use '-O list-all' to list features)"),
 	OPTLINE("-L|--label LABEL", "set the filesystem label"),
 	OPTLINE("-U|--uuid UUID", "specify the filesystem UUID (must be unique for a filesystem with multiple devices)"),
+	OPTLINE("--device-uuid UUID", "Specify the filesystem device UUID (a.k.a sub-uuid) (for single device filesystem only)"),
 	"Creation:",
 	OPTLINE("-b|--byte-count SIZE", "set size of each device to SIZE (filesystem size is sum of all device sizes)"),
 	OPTLINE("-r|--rootdir DIR", "copy files from DIR to the image root directory"),
@@ -1161,6 +1162,7 @@ int BOX_MAIN(mkfs)(int argc, char **argv)
 	struct btrfs_mkfs_features features = btrfs_mkfs_default_features;
 	enum btrfs_csum_type csum_type = BTRFS_CSUM_TYPE_CRC32;
 	char fs_uuid[BTRFS_UUID_UNPARSED_SIZE] = { 0 };
+	char dev_uuid[BTRFS_UUID_UNPARSED_SIZE] = { 0 };
 	u32 nodesize = 0;
 	bool nodesize_forced = false;
 	u32 sectorsize = 0;
@@ -1187,6 +1189,7 @@ int BOX_MAIN(mkfs)(int argc, char **argv)
 			GETOPT_VAL_SHRINK = GETOPT_VAL_FIRST,
 			GETOPT_VAL_CHECKSUM,
 			GETOPT_VAL_GLOBAL_ROOTS,
+			GETOPT_VAL_DEVICE_UUID,
 		};
 		static const struct option long_options[] = {
 			{ "byte-count", required_argument, NULL, 'b' },
@@ -1208,6 +1211,8 @@ int BOX_MAIN(mkfs)(int argc, char **argv)
 			{ "features", required_argument, NULL, 'O' },
 			{ "runtime-features", required_argument, NULL, 'R' },
 			{ "uuid", required_argument, NULL, 'U' },
+			{ "device-uuid", required_argument, NULL,
+				GETOPT_VAL_DEVICE_UUID },
 			{ "quiet", 0, NULL, 'q' },
 			{ "verbose", 0, NULL, 'v' },
 			{ "shrink", no_argument, NULL, GETOPT_VAL_SHRINK },
@@ -1332,6 +1337,9 @@ int BOX_MAIN(mkfs)(int argc, char **argv)
 			case 'q':
 				bconf_be_quiet();
 				break;
+			case GETOPT_VAL_DEVICE_UUID:
+				strncpy(dev_uuid, optarg, BTRFS_UUID_UNPARSED_SIZE - 1);
+				break;
 			case GETOPT_VAL_SHRINK:
 				shrink_rootdir = true;
 				break;
@@ -1373,6 +1381,10 @@ int BOX_MAIN(mkfs)(int argc, char **argv)
 		error("the option -r is limited to a single device");
 		goto error;
 	}
+	if (strlen(dev_uuid) != 0 && device_count > 1) {
+		error("the option --device-uuid is limited to a single device");
+		goto error;
+	}
 	if (shrink_rootdir && source_dir == NULL) {
 		error("the option --shrink must be used with --rootdir");
 		goto error;
@@ -1733,6 +1745,7 @@ int BOX_MAIN(mkfs)(int argc, char **argv)
 
 	mkfs_cfg.label = label;
 	memcpy(mkfs_cfg.fs_uuid, fs_uuid, sizeof(mkfs_cfg.fs_uuid));
+	memcpy(mkfs_cfg.dev_uuid, dev_uuid, sizeof(mkfs_cfg.dev_uuid));
 	mkfs_cfg.num_bytes = dev_block_count;
 	mkfs_cfg.nodesize = nodesize;
 	mkfs_cfg.sectorsize = sectorsize;