On Wed, Jun 30, 2021 at 09:26:20PM +0800, Qu Wenruo wrote:

quoted

Is there a way to list such subvolumes from progs?

No, root with 0 ref will not show up in "btrfs subv list".

We might need one then, but I'll read the full report, maybe it's a
one-off bug.

In fact unless we pass @check_ref = false, btrfs_get_fs_root() won't 
return such ghost root at all.

In progs the subvolumes are searched directly by the key, so this
(kernel function) is not relevant.