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

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On Sun, Mar 28, 2021 at 6:56 PM Amir Goldstein <amir73il@xxxxxxxxx> 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@xxxxxxxxxx>
> Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
> ---
>
> Jan,
>
> After trying several different approaches, I finally realized that
> making FAN_CREATE available for mount marks is not that hard and it could
> be very useful IMO.
>
> Adding support for other "inode events" with mount mark, such as
> FAN_ATTRIB, FAN_DELETE, FAN_MOVE may also be possible, but adding support
> for FAN_CREATE was really easy due to the fact that all call sites are
> already surrounded by filename_creat()/done_path_create() calls.
>

FWIW, adding support for FAN_DELETE and FAN_MOVE_SELF was not
so hard. The move event at least will also be needed for the use case
where watching when a negative path is instantiated.

https://github.com/amir73il/linux/commits/fsnotify_path_hooks

Thanks,
Amir.



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