btrfs: move common inode creation code into btrfs_create_new_inode()

All of our inode creation code paths duplicate the calls to
btrfs_init_inode_security() and btrfs_add_link(). Subvolume creation
additionally duplicates property inheritance and the call to
btrfs_set_inode_index(). Fix this by moving the common code into
btrfs_create_new_inode(). This accomplishes a few things at once:

1. It reduces code duplication.

2. It allows us to set up the inode completely before inserting the
   inode item, removing calls to btrfs_update_inode().

3. It fixes a leak of an inode on disk in some error cases. For example,
   in btrfs_create(), if btrfs_new_inode() succeeds, then we have
   inserted an inode item and its inode ref. However, if something after
   that fails (e.g., btrfs_init_inode_security()), then we end the
   transaction and then decrement the link count on the inode. If the
   transaction is committed and the system crashes before the failed
   inode is deleted, then we leak that inode on disk. Instead, this
   refactoring aborts the transaction when we can't recover more
   gracefully.

4. It exposes various ways that subvolume creation diverges from mkdir
   in terms of inheriting flags, properties, permissions, and POSIX
   ACLs, a lot of which appears to be accidental. This patch explicitly
   does _not_ change the existing non-standard behavior, but it makes
   those differences more clear in the code and documents them so that
   we can discuss whether they should be changed.

Reviewed-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 5 insertions, 40 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index bd10b8d44b5d..fe00dd88c281 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -575,8 +575,6 @@ static noinline int create_subvol(struct user_namespace *mnt_userns,
 				  struct inode *dir, struct dentry *dentry,
 				  struct btrfs_qgroup_inherit *inherit)
 {
-	const char *name = dentry->d_name.name;
-	int namelen = dentry->d_name.len;
 	struct btrfs_fs_info *fs_info = btrfs_sb(dir->i_sb);
 	struct btrfs_trans_handle *trans;
 	struct btrfs_key key;
@@ -596,7 +594,6 @@ static noinline int create_subvol(struct user_namespace *mnt_userns,
 	int ret;
 	dev_t anon_dev;
 	u64 objectid;
-	u64 index = 0;
 
 	root_item = kzalloc(sizeof(*root_item), GFP_KERNEL);
 	if (!root_item)
@@ -713,7 +710,6 @@ static noinline int create_subvol(struct user_namespace *mnt_userns,
 	free_extent_buffer(leaf);
 	leaf = NULL;
 
-	key.offset = (u64)-1;
 	new_root = btrfs_get_new_fs_root(fs_info, objectid, anon_dev);
 	if (IS_ERR(new_root)) {
 		ret = PTR_ERR(new_root);
@@ -731,47 +727,21 @@ static noinline int create_subvol(struct user_namespace *mnt_userns,
 		goto out;
 	}
 
-	ret = btrfs_create_subvol_root(trans, root, &new_inode_args);
-	if (ret) {
-		/* We potentially lose an unused inode item here */
-		btrfs_abort_transaction(trans, ret);
-		goto out;
-	}
-
-	/*
-	 * insert the directory item
-	 */
-	ret = btrfs_set_inode_index(BTRFS_I(dir), &index);
-	if (ret) {
-		btrfs_abort_transaction(trans, ret);
-		goto out;
-	}
-
-	ret = btrfs_insert_dir_item(trans, name, namelen, BTRFS_I(dir), &key,
-				    BTRFS_FT_DIR, index);
-	if (ret) {
-		btrfs_abort_transaction(trans, ret);
-		goto out;
-	}
-
-	btrfs_i_size_write(BTRFS_I(dir), dir->i_size + namelen * 2);
-	ret = btrfs_update_inode(trans, root, BTRFS_I(dir));
+	ret = btrfs_uuid_tree_add(trans, root_item->uuid,
+				  BTRFS_UUID_KEY_SUBVOL, objectid);
 	if (ret) {
 		btrfs_abort_transaction(trans, ret);
 		goto out;
 	}
 
-	ret = btrfs_add_root_ref(trans, objectid, root->root_key.objectid,
-				 btrfs_ino(BTRFS_I(dir)), index, name, namelen);
+	ret = btrfs_create_new_inode(trans, &new_inode_args);
 	if (ret) {
 		btrfs_abort_transaction(trans, ret);
 		goto out;
 	}
 
-	ret = btrfs_uuid_tree_add(trans, root_item->uuid,
-				  BTRFS_UUID_KEY_SUBVOL, objectid);
-	if (ret)
-		btrfs_abort_transaction(trans, ret);
+	d_instantiate_new(dentry, new_inode_args.inode);
+	new_inode_args.inode = NULL;
 
 out:
 	trans->block_rsv = NULL;
@@ -782,11 +752,6 @@ out:
 		btrfs_end_transaction(trans);
 	else
 		ret = btrfs_commit_transaction(trans);
-
-	if (!ret) {
-		d_instantiate(dentry, new_inode_args.inode);
-		new_inode_args.inode = NULL;
-	}
 out_new_inode_args:
 	btrfs_new_inode_args_destroy(&new_inode_args);
 out_inode: