Re: [PATCH v2] btrfs: reject refs=0 subvolume without DEAD in SUBVOL_SYNC_WAIT

[David Sterba]

On Sun, Nov 01, 2026 at 05:48:21PM +1030, Qu Wenruo wrote:
> With that said, there are more problems with the ioctl.
> 
> - No real user
>    No one is utilizing BTRFS_SUBVOL_SYNC* flags. Btrfs-progs itself
>    doesn't even bother it.
> 
>    So all these fixes are very low priority, unless there are some wild
>    programs utilizing this.
> 
>    But even btrfs-progs doesn't utilize them, the possibility are very
>    low.

Obviously the ioctl was added so progs 'subvol sync' can use it for
non-root users. I started working on it but there's a problem with the
behaviour change between the user types. Root has full access and
reports the progress while with this ioctl there were some problems I
don't remember. The ioctl was designed to emulate all modes that root
can do so it should be possible to get 1:1 output.