Re: [RFC][PATCH] fanotify: allow setting FAN_CREATE in mount mark mask

[Amir Goldstein <amir73il@gmail.com>]

On Tue, Mar 30, 2021 at 10:31 AM Christian Brauner
<christian.brauner@ubuntu.com> wrote:
>
> On Sun, Mar 28, 2021 at 06:56:24PM +0300, Amir Goldstein wrote:
> > Add a high level hook fsnotify_path_create() which is called from
> > syscall context where mount context is available, so that FAN_CREATE
> > event can be added to a mount mark mask.
> >
> > This high level hook is called in addition to fsnotify_create(),
> > fsnotify_mkdir() and fsnotify_link() hooks in vfs helpers where the mount
> > context is not available.
> >
> > In the context where fsnotify_path_create() will be called, a dentry flag
> > flag is set on the new dentry the suppress the FS_CREATE event in the vfs
> > level hooks.
> >
> > This functionality was requested by Christian Brauner to replace
> > recursive inotify watches for detecting when some path was created under
> > an idmapped mount without having to monitor FAN_CREATE events in the
> > entire filesystem.
> >
> > In combination with more changes to allow unprivileged fanotify listener
> > to watch an idmapped mount, this functionality would be usable also by
> > nested container managers.
> >
> > Link: https://lore.kernel.org/linux-fsdevel/20210318143140.jxycfn3fpqntq34z@wittgenstein/
> > Cc: Christian Brauner <christian.brauner@ubuntu.com>
> > Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> > ---
>
> Was about to look at this. Does this require preliminary patches since
> it doesn't apply to current master. If so, can you just give me a link
> to a branch so I can pull from that? :)
>

The patch is less useful on its own.
Better take the entire work for the demo which includes this patch:

[1] https://github.com/amir73il/linux/commits/fanotify_userns
[2] https://github.com/amir73il/inotify-tools/commits/fanotify_userns

Thanks,
Amir.