[PATCH v4 4/4] vfs: add notifications for mount attribute change

[Christian Brauner]

On Fri, Jan 24, 2025 at 04:49:28PM +0100, Miklos Szeredi wrote:
> On Fri, 24 Jan 2025 at 16:38, Christian Brauner <brauner at kernel.org> wrote:
> >
> > On Thu, Jan 23, 2025 at 08:41:07PM +0100, Miklos Szeredi wrote:
> > > Notify when mount flags, propagation or idmap changes.
> > >
> > > Just like attach and detach, no details are given in the notification, only
> > > the mount ID.
> > >
> > > Signed-off-by: Miklos Szeredi <mszeredi at redhat.com>
> > > ---
> >
> > I think this is a good next step but I would first go with the minimal
> > functionality of notifying about mount topology changes for v6.15.
> 
> I can totally relate to that.   I added the fourth patch more as a
> "let's see if this can also fit into the current framework".
> 
> > Btw, if we notify in do_remount() on the mount that triggered
> > superblock reconfiguration then we also need to trigger in
> > vfs_cmd_reconfigure() aka fsconfig(FSCONFIG_CMD_RECONFIGURE) but the
> > mount that was used to change superblock options is only available in
> > fspick() currently. That would need to be handled.
> 
> No, if we'd want to watch changes on super blocks, then we'd need to
> iterate all the mounts of the superblock and notify each.

Ah, I remember that old remount had unclear semantics where mount
specific and superblock specific options are interleaved. So we would
need to notify from do_remount() on mount specific changes. Right, then
this change is correct and I agree about the superblock part.