Btrfs: Add backrefs and forward refs for subvols and snapshots

Subvols and snapshots can now be referenced from any point in the directory
tree.  We need to maintain back refs for them so we can find lost
subvols.

Forward refs are added so that we know all of the subvols and
snapshots referenced anywhere in the directory tree of a single subvol.  This
can be used to do recursive snapshotting (but they aren't yet) and it is
also used to detect and prevent directory loops when creating new snapshots.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 23 insertions, 8 deletions

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 93f23a456a36..e9c8ebeedd7e 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -831,28 +831,43 @@ static noinline int finish_pending_snapshot(struct btrfs_fs_info *fs_info,
         struct btrfs_trans_handle *trans;
         struct inode *parent_inode;
         struct inode *inode;
+        struct btrfs_root *parent_root;
 
         parent_inode = pending->dentry->d_parent->d_inode;
-        trans = btrfs_start_transaction(BTRFS_I(parent_inode)->root, 1);
+        parent_root = BTRFS_I(parent_inode)->root;
+        trans = btrfs_start_transaction(parent_root, 1);
 
         /*
          * insert the directory item
          */
         namelen = strlen(pending->name);
         ret = btrfs_set_inode_index(parent_inode, &index);
-        ret = btrfs_insert_dir_item(trans,
-                            BTRFS_I(parent_inode)->root,
+        ret = btrfs_insert_dir_item(trans, parent_root,
                             pending->name, namelen,
                             parent_inode->i_ino,
                             &pending->root_key, BTRFS_FT_DIR, index);
 
         if (ret)
                 goto fail;
-#if 0
-        ret = btrfs_insert_inode_ref(trans, root->fs_info->tree_root,
-                             pending->name, strlen(pending->name), objectid,
-                             root->fs_info->sb->s_root->d_inode->i_ino, 0);
-#endif
+
+        /* add the backref first */
+        ret = btrfs_add_root_ref(trans, parent_root->fs_info->tree_root,
+                                 pending->root_key.objectid,
+                                 BTRFS_ROOT_BACKREF_KEY,
+                                 parent_root->root_key.objectid,
+                                 parent_inode->i_ino, index, pending->name,
+                                 namelen);
+
+        BUG_ON(ret);
+
+        /* now add the forward ref */
+        ret = btrfs_add_root_ref(trans, parent_root->fs_info->tree_root,
+                                 parent_root->root_key.objectid,
+                                 BTRFS_ROOT_REF_KEY,
+                                 pending->root_key.objectid,
+                                 parent_inode->i_ino, index, pending->name,
+                                 namelen);
+
         inode = btrfs_lookup_dentry(parent_inode, pending->dentry);
         d_instantiate(pending->dentry, inode);
 fail: