linux-kernel - Re: [PATCH 3/4] inotify_user: add system call inotify_add_watch

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Date:   Mon, 18 Sep 2023 14:40:50 +0200
From:   Jan Kara <jack@...e.cz>
To:     Max Kellermann <max.kellermann@...os.com>
Cc:     jack@...e.cz, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, amir73il@...il.com
Subject: Re: [PATCH 3/4] inotify_user: add system call inotify_add_watch_at()

On Mon 18-09-23 14:32:16, Max Kellermann wrote:
> This implements a missing piece in the inotify API: referring to a
> file by a directory file descriptor and a path name.  This can be
> solved in userspace currently only by doing something similar to:
> 
>   int old = open(".");
>   fchdir(dfd);
>   inotify_add_watch(....);
>   fchdir(old);
> 
> Support for LOOKUP_EMPTY is still missing.  We could add another IN_*
> flag for that (which would clutter the IN_* flags list further) or
> add a "flags" parameter to the new system call (which would however
> duplicate features already present via special IN_* flags).
> 
> To: Jan Kara <jack@...e.cz>
> Cc: Amir Goldstein <amir73il@...il.com>
> To: linux-fsdevel@...r.kernel.org
> To: linux-kernel@...r.kernel.org
> Signed-off-by: Max Kellermann <max.kellermann@...os.com>

Thanks for the patches! But generally we don't add new functionality to the
inotify API and rather steer users towards fanotify. In this particular
case fanotify_mark(2) already has the support for dirfd + name. Is there
any problem with using fanotify for you? Note that since kernel 5.13 you
don't need CAP_SYS_ADMIN capability for fanotify functionality that is
more-or-less equivalent to what inotify provides.

								Honza

> ---
>  fs/notify/inotify/inotify_user.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c
> index b6e6f6ab21f8..8a9096c5ebb1 100644
> --- a/fs/notify/inotify/inotify_user.c
> +++ b/fs/notify/inotify/inotify_user.c
> @@ -797,6 +797,12 @@ SYSCALL_DEFINE3(inotify_add_watch, int, fd, const char __user *, pathname,
>  	return do_inotify_add_watch(fd, AT_FDCWD, pathname, mask);
>  }
>  
> +SYSCALL_DEFINE4(inotify_add_watch_at, int, fd, int, dfd, const char __user *, pathname,
> +		u32, mask)
> +{
> +	return do_inotify_add_watch(fd, dfd, pathname, mask);
> +}
> +
>  SYSCALL_DEFINE2(inotify_rm_watch, int, fd, __s32, wd)
>  {
>  	struct fsnotify_group *group;
> -- 
> 2.39.2
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR