On Tue, Oct 24, 2023 at 9:01 PM Benjamin Coddington <bcodding@xxxxxxxxxx> wrote:
>
> On 24 Oct 2023, at 13:12, Amir Goldstein wrote:
> > On Tue, Oct 24, 2023 at 6:32 PM Benjamin Coddington <bcodding@xxxxxxxxxx> wrote:
> >> Yes, but if the specific export is on the same server's filesystem as the
> >> "root", you'll still get zero. There are various ways to set fsid on
> >> exports for linux servers, but the fsid will be the same for all exports of
> >> the same filesystem on the server.
> >>
> >
> > OK. good to know. I thought zero fsid was only for the root itself.
>
> Yes, but by "root" here I always mean the special NFSv4 root - the special
> per-server global root filehandle.
>
> ...
>
> >> I'm not familiar with fanotify enough to know if having multiple fsid 0
> >> mounts of different filesystems on different servers will do the right
> >> thing. I wanted to point out that very real possibility for v4.
> >>
> >
> > The fact that fsid 0 would be very common for many nfs mounts
> > makes this patch much less attractive.
> >
> > Because we only get events for local client changes, we do not
> > have to tie the fsid with the server's fsid, we could just use a local
> > volatile fsid, as we do in other non-blockdev fs (tmpfs, kernfs).
>
> A good way to do this would be to use the nfs_server->s_dev's major:minor -
> this represents the results of nfs_compare_super(), so it should be the same
> value if NFS is treating it as the same filesystem.
>
Yes, that would avoid local collisions and this is what we are going
to do for most of the simple fs with anon_bdev [1].
But anon_bdev major is 0 and minor is quickly recyclable.
fanotify identified objects by {f_fsid, f_handle} pair.
Since nfs client encodes persistent file handles, I would like to try to hold
its f_fsid to higher standards than those of the simple fs.
You say that server->fsid.minor is always 0.
Perhaps we should mix server->fsid.major with server->s_dev's minor?
Thanks,
Amir.
[1] https://lore.kernel.org/linux-fsdevel/20231023143049.2944970-1-amir73il@xxxxxxxxx/
