Btrfs: add snapshot/subvolume destroy ioctl

This patch adds snapshot/subvolume destroy ioctl.  A subvolume that isn't being
used and doesn't contains links to other subvolumes can be destroyed.

Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 7 insertions, 3 deletions

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 915077725fea..88f866f85e7a 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -104,7 +104,6 @@ static noinline int record_root_in_trans(struct btrfs_trans_handle *trans,
 {
         if (root->ref_cows && root->last_trans < trans->transid) {
                 WARN_ON(root == root->fs_info->extent_root);
-                WARN_ON(root->root_item.refs == 0);
                 WARN_ON(root->commit_root != root->node);
 
                 radix_tree_tag_set(&root->fs_info->fs_roots_radix,
@@ -1078,8 +1077,13 @@ int btrfs_clean_old_snapshots(struct btrfs_root *root)
 
         while (!list_empty(&list)) {
                 root = list_entry(list.next, struct btrfs_root, root_list);
-                list_del_init(&root->root_list);
-                btrfs_drop_snapshot(root, 0);
+                list_del(&root->root_list);
+
+                if (btrfs_header_backref_rev(root->node) <
+                    BTRFS_MIXED_BACKREF_REV)
+                        btrfs_drop_snapshot(root, 0);
+                else
+                        btrfs_drop_snapshot(root, 1);
         }
         return 0;
 }