linux-kernel - Re: [PATCH] VFS: generate FS_CREATE before FS_OPEN when ->atomic

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Date: Wed, 12 Jun 2024 04:14:04 +0100
From: Al Viro <viro@...iv.linux.org.uk>
To: NeilBrown <neilb@...e.de>
Cc: Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	Amir Goldstein <amir73il@...il.com>,
	James Clark <james.clark@....com>, ltp@...ts.linux.it,
	linux-nfs@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] VFS: generate FS_CREATE before FS_OPEN when
 ->atomic_open used.

On Wed, Jun 12, 2024 at 12:55:40PM +1000, NeilBrown wrote:
> > 	IF we don't care about that, we might as well take fsnotify_open()
> > out of vfs_open() and, for do_open()/do_tmpfile()/do_o_path(), into
> > path_openat() itself.  I mean, having
> >         if (likely(!error)) {
> >                 if (likely(file->f_mode & FMODE_OPENED)) {
> > 			fsnotify_open(file);
> >                         return file;
> > 		}
> > in there would be a lot easier to follow...  It would lose fsnotify_open()
> > in a few more failure exits, but if we don't give a damn about having it
> > paired with fsnotify_close()...
> > 
> 
> Should we have fsnotify_open() set a new ->f_mode flag, and
> fsnotify_close() abort if it isn't set (and clear it if it is)?
> Then we would be guaranteed a balance - which does seem like a good
> idea.

Umm...  In that case, I would rather have FMODE_NONOTIFY set just before
the fput() in path_openat() - no need to grab another flag from ->f_mode
(not a lot of unused ones there) and no need to add any overhead on
the fast path.