Re: [PATCH 0/3] fanotify support for btrfs sub-volumes

Jan Kara
2023-10-27T10:58:23Z

On Thu 26-10-23 22:44:26, Christoph Hellwig wrote:
> On Wed, Oct 25, 2023 at 07:04:45PM +0200, Jan Kara wrote:
> > Well, this is the discussion how btrfs should be presenting its subvolumes
> > to VFS / userspace, isn't it?
>
> Yes. Which we've pressured to resolve forever, but it's been ignored.
>
> > I never dived into that too closely but as
> > far as I remember it was discussed to death without finding an acceptable
> > (to all parties) solution? I guess having a different fsid per subvolume
> > makes sense (and we can't change that given it is like that forever even if
> > we wanted). Having different subvolumes share one superblock is more
> > disputable but there were reasons for that as well. So I'm not sure how you
> > imagine to resolve this...
>
> We need to solve this out kernel wide, and right now the kernel doesn't
> support different dev_t / fsids inside a single file syste at all.
> SuSE hacks around that badly for limited user interfaces with the
> horrible get_inode_dev method they've added, but this has been rejected
> upstream for good reason. What this series does is to add another
> limited version of this through the backdoor.

OK, I see. I agree adding ->get_fsid is just piling on top of the problems
so I can see why you don't like it. Band aids are double-edged sword ;)

Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR