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From:   Benjamin Coddington <bcodding@redhat.com>
To:     Amir Goldstein <amir73il@gmail.com>
Cc:     Trond Myklebust <trond.myklebust@hammerspace.com>,
        Anna Schumaker <anna@kernel.org>,
        Jeff Layton <jlayton@kernel.org>,
        Chuck Lever <chuck.lever@oracle.com>,
        Christian Brauner <brauner@kernel.org>,
        Jan Kara <jack@suse.cz>, linux-fsdevel@vger.kernel.org,
        linux-nfs@vger.kernel.org
Subject: Re: [PATCH] nfs: derive f_fsid from server's fsid
Date:   Tue, 24 Oct 2023 14:00:53 -0400
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On 24 Oct 2023, at 13:12, Amir Goldstein wrote:
> On Tue, Oct 24, 2023 at 6:32 PM Benjamin Coddington <bcodding@redhat.com> 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.

> I am not decisive about the best way to tackle this and since
> Jan was not sure about the value of local-only notifications
> for network filesystems, I am going to put this one on hold.
>
> Thanks for the useful feedback!

Sure!

Ben