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

[David Sterba <dsterba@suse.cz>]

On Tue, Nov 10, 2026 at 07:00:34AM +1030, Qu Wenruo wrote:
> 
> 
> 在 2026/11/10 05:17, David Sterba 写道:
> > 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.
> 
> Are you still planning to implement the full root-less subvolume wait in 
> progs?

Yes, but I don't have an ETA.

> Or is this feature deprecated and we can eventually remove it to reduce 
> LLM bug reports?

I don't understand what would need to be deprecated, it's a new ioctl
missing the userspace counterpart to implement an unprivileged
functionality where it makes sense.