btrfs-progs: mkfs: add ro flag to --subvol

Adds a flag to mkfs.btrfs --subvol to allow subvolumes to be created
readonly.

Signed-off-by: Mark Harmstone <maharmstone@fb.com>

Documentation/mkfs.btrfs.rst

@@ -163,6 +163,7 @@ OPTIONS
         *flags* is an optional comma-separated list of modifiers. Valid choices are:
 
         * *default*: create as default subvolume (this can only be specified once)
+        * *ro*: create as readonly subvolume
 
 --shrink
         Shrink the filesystem to its minimal size, only works with *--rootdir* option.

common/root-tree-utils.c

@@ -66,7 +66,8 @@ error:
  * The created tree root would have its root_ref as 1.
  * Thus for subvolumes caller needs to properly add ROOT_BACKREF items.
  */
-int btrfs_make_subvolume(struct btrfs_trans_handle *trans, u64 objectid)
+int btrfs_make_subvolume(struct btrfs_trans_handle *trans, u64 objectid,
+			 bool readonly)
 {
 	struct btrfs_fs_info *fs_info = trans->fs_info;
 	struct btrfs_root *root;
@@ -98,6 +99,13 @@ int btrfs_make_subvolume(struct btrfs_trans_handle *trans, u64 objectid)
 	ret = btrfs_make_root_dir(trans, root, BTRFS_FIRST_FREE_OBJECTID);
 	if (ret < 0)
 		goto error;
+
+	btrfs_set_stack_inode_flags(&root->root_item.inode,
+				    BTRFS_INODE_ROOT_ITEM_INIT);
+
+	if (readonly)
+		btrfs_set_root_flags(&root->root_item, BTRFS_ROOT_SUBVOL_RDONLY);
+
 	ret = btrfs_update_root(trans, fs_info->tree_root, &root->root_key,
 				&root->root_item);
 	if (ret < 0)

common/root-tree-utils.h

@@ -21,7 +21,8 @@
 
 int btrfs_make_root_dir(struct btrfs_trans_handle *trans,
 			struct btrfs_root *root, u64 objectid);
-int btrfs_make_subvolume(struct btrfs_trans_handle *trans, u64 objectid);
+int btrfs_make_subvolume(struct btrfs_trans_handle *trans, u64 objectid,
+			 bool readonly);
 int btrfs_link_subvolume(struct btrfs_trans_handle *trans,
 			 struct btrfs_root *parent_root,
 			 u64 parent_dir, const char *name,

convert/main.c

@@ -1022,13 +1022,14 @@ static int init_btrfs(struct btrfs_mkfs_config *cfg, struct btrfs_root *root,
 			     BTRFS_FIRST_FREE_OBJECTID);
 
 	/* subvol for fs image file */
-	ret = btrfs_make_subvolume(trans, CONV_IMAGE_SUBVOL_OBJECTID);
+	ret = btrfs_make_subvolume(trans, CONV_IMAGE_SUBVOL_OBJECTID, false);
 	if (ret < 0) {
 		error("failed to create subvolume image root: %d", ret);
 		goto err;
 	}
 	/* subvol for data relocation tree */
-	ret = btrfs_make_subvolume(trans, BTRFS_DATA_RELOC_TREE_OBJECTID);
+	ret = btrfs_make_subvolume(trans, BTRFS_DATA_RELOC_TREE_OBJECTID,
+				   false);
 	if (ret < 0) {
 		error("failed to create DATA_RELOC root: %d", ret);
 		goto err;

mkfs/main.c

@@ -1036,6 +1036,8 @@ static int parse_subvol_flags(struct rootdir_subvol *subvol, const char *flags)
 
 		if (!strcmp(buf, "default")) {
 			subvol->is_default = true;
+		} else if (!strcmp(buf, "ro")) {
+			subvol->readonly = true;
 		} else if (buf[0] != 0) {
 			error("unrecognized subvol flag \"%s\"", buf);
 			ret = 1;
@@ -1988,7 +1990,8 @@ raid_groups:
 		goto out;
 	}
 
-	ret = btrfs_make_subvolume(trans, BTRFS_DATA_RELOC_TREE_OBJECTID);
+	ret = btrfs_make_subvolume(trans, BTRFS_DATA_RELOC_TREE_OBJECTID,
+				   false);
 	if (ret) {
 		error("unable to create data reloc tree: %d", ret);
 		goto out;

mkfs/rootdir.c

@@ -430,7 +430,7 @@ static int ftw_add_subvol(const char *full_path, const struct stat *st,
 
 	subvol_id = next_subvol_id++;
 
-	ret = btrfs_make_subvolume(g_trans, subvol_id);
+	ret = btrfs_make_subvolume(g_trans, subvol_id, subvol->readonly);
 	if (ret < 0) {
 		errno = -ret;
 		error("failed to create subvolume: %m");

mkfs/rootdir.h

@@ -33,6 +33,7 @@ struct rootdir_subvol {
 	char *dir;
 	char *full_path;
 	bool is_default;
+	bool readonly;
 };
 
 int btrfs_mkfs_fill_dir(struct btrfs_trans_handle *trans, const char *source_dir,