linux-ext4 - Re: [PATCH 1/4] fs: send uevents for filesystem mount events

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Message-ID: <20260105172618.GB191481@frogsfrogsfrogs>
Date: Mon, 5 Jan 2026 09:26:18 -0800
From: "Darrick J. Wong" <djwong@...nel.org>
To: Ian Kent <raven@...maw.net>
Cc: Christian Brauner <brauner@...nel.org>, linux-ext4@...r.kernel.org,
	linux-xfs@...r.kernel.org, hch@....de,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 1/4] fs: send uevents for filesystem mount events

On Sat, Dec 27, 2025 at 07:58:10AM +0800, Ian Kent wrote:
> 
> On 24/12/25 20:47, Christian Brauner wrote:
> > On Wed, Dec 17, 2025 at 06:04:29PM -0800, Darrick J. Wong wrote:
> > > From: Darrick J. Wong <djwong@...nel.org>
> > > 
> > > Add the ability to send uevents whenever a filesystem mounts, unmounts,
> > > or goes down.  This will enable XFS to start daemons whenever a
> > > filesystem is first mounted.
> > > 
> > > Regrettably, we can't wire this directly into get_tree_bdev_flags or
> > > generic_shutdown_super because not all filesystems set up a kobject
> > > representation in sysfs, and the VFS has no idea if a filesystem
> > > actually does that.
> > > 
> > > Signed-off-by: "Darrick J. Wong" <djwong@...nel.org>
> > > ---
> > I have issues with uevents as a mechanism for this. Uevents are tied to
> > network namespaces and they are not really namespaced appropriately. Any
> > filesystem that hooks into this mechanism will spew uevents into the
> > initial network namespace unconditionally. Any container mountable
> > filesystem that wants to use this interface will spam the host with
> > this event though the even is completely useless without appropriate
> > meta information about the relevant mount namespaces and further
> > parameters. This is a design dead end going forward imho. So please
> > let's not do this.
> > 
> > Instead ties this to fanotify which is the right interface for this.
> > My suggestion would be to tie this to mount namespaces as that's the
> > appropriate object. Fanotify already supports listening for general
> > mount/umount events on mount namespaces. So extend it to send filesystem
> > creation/destruction events so that a caller may listen on the initial
> > mount namespace - where xfs fses can be mounted - you could even make it
> > filterable per filesystem type right away.
> 
> Seconded, there are way too many sources of mount events for them to not
> 
> be specific and targeted.

NP, thanks to you both for the quick feedback. :)

--D

> 
> Just my opinion, ;),
> 
> Ian
> 
>