btrfs: automatically remove the subvolume qgroup

Currently if we fully clean a subvolume (not only delete its directory,
but fully clean all it's related data and root item), the associated
qgroup would not be removed.

We have "btrfs qgroup clear-stale" to handle such 0 level qgroups.

Change the behavior to automatically removie the qgroup of a fully
cleaned subvolume when possible:

- Full qgroup but still consistent
  We can and should remove the qgroup.
  The qgroup numbers should be 0, without any rsv.

- Full qgroup but inconsistent
  Can happen with drop_subtree_threshold feature (skip accounting
  and mark qgroup inconsistent).

  We can and should remove the qgroup.
  Higher level qgroup numbers will be incorrect, but since qgroup
  is already inconsistent, it should not be a problem.

- Squota mode
  This is the special case, we can only drop the qgroup if its numbers
  are all 0.

  This would be handled by can_delete_qgroup(), so we only need to check
  the return value and ignore the -EBUSY error.

Link: https://bugzilla.suse.com/show_bug.cgi?id=1222847
Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 3774c191e36d..32f03c0a7b9e 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -5833,6 +5833,7 @@ int btrfs_drop_snapshot(struct btrfs_root *root, int update_ref, int for_reloc)
 	struct btrfs_root_item *root_item = &root->root_item;
 	struct walk_control *wc;
 	struct btrfs_key key;
+	const u64 rootid = btrfs_root_id(root);
 	int err = 0;
 	int ret;
 	int level;
@@ -6063,6 +6064,13 @@ out_free:
 	kfree(wc);
 	btrfs_free_path(path);
 out:
+	if (!err && root_dropped) {
+		ret = btrfs_qgroup_cleanup_dropped_subvolume(fs_info, rootid);
+		if (ret < 0)
+			btrfs_warn_rl(fs_info,
+				      "failed to cleanup qgroup 0/%llu: %d",
+				      rootid, ret);
+	}
 	/*
 	 * We were an unfinished drop root, check to see if there are any
 	 * pending, and if not clear and wake up any waiters.