[PATCH 2/2] btrfs: automatically remove the subvolume qgroup

[Qu Wenruo <wqu@suse.com>]

Currently if we fully removed a subvolume (not only unlinked, but fully
dropped its root item), its qgroup would not be removed.

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

This patch changes the behavior by automatically removing the qgroup of
a fully dropped subvolume.

Link: https://bugzilla.suse.com/show_bug.cgi?id=1222847
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/extent-tree.c |  9 +++++++++
 fs/btrfs/qgroup.c      | 28 ++++++++++++++++++++++++++++
 fs/btrfs/qgroup.h      |  2 ++
 3 files changed, 39 insertions(+)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 023920d0d971..f4887f05a819 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -5834,6 +5834,7 @@ 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;
@@ -6064,6 +6065,14 @@ int btrfs_drop_snapshot(struct btrfs_root *root, int update_ref, int for_reloc)
 	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.
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index e6fcce4372a4..8690e212ba2a 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -1838,6 +1838,34 @@ int btrfs_remove_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid)
 	return ret;
 }
 
+int btrfs_qgroup_cleanup_dropped_subvolume(struct btrfs_fs_info *fs_info,
+					   u64 subvolid)
+{
+	struct btrfs_trans_handle *trans;
+	int ret;
+
+	if (!is_fstree(subvolid) || !btrfs_qgroup_enabled(fs_info) ||
+	    !fs_info->quota_root)
+		return 0;
+
+	/* Commit current transaction to ensure the root item is removed. */
+	trans = btrfs_start_transaction(fs_info->quota_root, 0);
+	if (IS_ERR(trans))
+		return PTR_ERR(trans);
+
+	ret = btrfs_commit_transaction(trans);
+	if (ret < 0)
+		return ret;
+
+	/* Start new trans to delete the qgroup info and limit items. */
+	trans = btrfs_start_transaction(fs_info->quota_root, 2);
+	if (IS_ERR(trans))
+		return PTR_ERR(trans);
+	ret = btrfs_remove_qgroup(trans, subvolid);
+	btrfs_end_transaction(trans);
+	return ret;
+}
+
 int btrfs_limit_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid,
 		       struct btrfs_qgroup_limit *limit)
 {
diff --git a/fs/btrfs/qgroup.h b/fs/btrfs/qgroup.h
index 706640be0ec2..3f93856a02e1 100644
--- a/fs/btrfs/qgroup.h
+++ b/fs/btrfs/qgroup.h
@@ -327,6 +327,8 @@ int btrfs_del_qgroup_relation(struct btrfs_trans_handle *trans, u64 src,
 			      u64 dst);
 int btrfs_create_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid);
 int btrfs_remove_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid);
+int btrfs_qgroup_cleanup_dropped_subvolume(struct btrfs_fs_info *fs_info,
+					   u64 subvolid);
 int btrfs_limit_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid,
 		       struct btrfs_qgroup_limit *limit);
 int btrfs_read_qgroup_config(struct btrfs_fs_info *fs_info);
-- 
2.44.0