Re: [PATCH] nfs: derive f_fsid from server's fsid

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 10:01:07 -0400	[thread overview]
Message-ID: <1CFE0178-CE91-4C99-B43E-33EF78D0BEBF@redhat.com> (raw)
In-Reply-To: <20231024110109.3007794-1-amir73il@gmail.com>

On 24 Oct 2023, at 7:01, Amir Goldstein wrote:

> Fold the server's 128bit fsid to report f_fsid in statfs(2).
> This is similar to how uuid is folded for f_fsid of ext2/ext4/zonefs.
>
> This allows nfs client to be monitored by fanotify filesystem watch
> for local client access if nfs supports re-export.
>
> For example, with inotify-tools 4.23.8.0, the following command can be
> used to watch local client access over entire nfs filesystem:
>
>   fsnotifywatch --filesystem /mnt/nfs
>
> Note that fanotify filesystem watch does not report remote changes on
> server.  It provides the same notifications as inotify, but it watches
> over the entire filesystem and reports file handle of objects and fsid
> with events.

I think this will run into trouble where an NFSv4 will report both
fsid.major and fsid.minor as zero for the special root filesystem.   We can
expect an NFSv4 client to have one of these per server.

Could use s_dev from nfs_server for a unique major/minor for each mount on
the client, but these values won't be stable against a particular server
export.

Ben