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

Christoph Hellwig
2023-10-27T05:44:36Z

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.