[PATCH 1/2] btrfs: forbid creating subvol qgroups

[Boris Burkov <boris@bur.io>]

This leads to various races and it isn't helpful, because you can't
specify a subvol id when creating a subvol, so you can't be sure it
will be the right one. Any requirements on the automatic subvol can
be gratified by using a higher level qgroup and the inheritance
parameters of subvol creation.

Signed-off-by: Boris Burkov <boris@bur.io>
---
 fs/btrfs/ioctl.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 58e0c59bc4cd..3d476decde52 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3815,6 +3815,11 @@ static long btrfs_ioctl_qgroup_create(struct file *file, void __user *arg)
 		goto out;
 	}
 
+	if (sa->create && is_fstree(sa->qgroupid)) {
+		ret = -EINVAL;
+		goto out;
+	}
+
 	trans = btrfs_join_transaction(root);
 	if (IS_ERR(trans)) {
 		ret = PTR_ERR(trans);
-- 
2.43.0