linux-ext4 - Re: [PATCH v7 05/18] fsnotify: introduce pre-content permission events

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Message-ID: <CAOQ4uxjeWrJtcgsC0YEmjdMPBOOpfz=zQ9VuG=z-Sc6WYNJOjQ@mail.gmail.com>
Date: Wed, 13 Nov 2024 19:49:31 +0100
From: Amir Goldstein <amir73il@...il.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Josef Bacik <josef@...icpanda.com>, kernel-team@...com, linux-fsdevel@...r.kernel.org, 
	jack@...e.cz, brauner@...nel.org, linux-xfs@...r.kernel.org, 
	linux-btrfs@...r.kernel.org, linux-mm@...ck.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH v7 05/18] fsnotify: introduce pre-content permission events

On Wed, Nov 13, 2024 at 5:57 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Tue, 12 Nov 2024 at 16:06, Amir Goldstein <amir73il@...il.com> wrote:
> >
> > Maybe I could use just this one bit, but together with the existing
> > FMODE_NONOTIFY bit, I get 4 modes, which correspond to the
> > highest watching priority:
>
> So you'd use two bits, but one of those would re-use the existing
> FMODE_NONOTIFY? That sounds perfectly fine to me.
>

Yes, exactly, like this:

/*
 * The two FMODE_NONOTIFY_ bits used together have a special meaning of
 * not reporting any events at all including non-permission events.
 * These are the possible values of FMODE_NOTIFY(f->f_mode) and their meaning:
 *
 * FMODE_NONOTIFY_HSM - suppress only pre-content events.
 * FMODE_NONOTIFY_PERM - suppress permission (incl. pre-content) events.
 * FMODE_NONOTIFY - suppress all (incl. non-permission) events.
 */
#define FMODE_NONOTIFY_MASK \
        (FMODE_NONOTIFY_HSM | FMODE_NONOTIFY_PERM)
#define FMODE_NONOTIFY FMODE_NONOTIFY_MASK
#define FMODE_NOTIFY(mode) \
        ((mode) & FMODE_NONOTIFY_MASK)

Please see attached patch (build and sanity tested) to make sure that
we are on the same page.

Going forward in the patch series, the choice of the NONOTIFY lingo
creates some double negatives, like:

        /*
         * read()/write() and other types of access generate pre-content events.
         */
        if (!likely(file->f_mode & FMODE_NONOTIFY_HSM)) {
                int ret = fsnotify_path(&file->f_path);

But it was easier for me to work with NONOTIFY flags.

Thanks,
Amir.

View attachment "0001-fsnotify-opt-in-for-permission-events-at-file-open-t.patch" of type "text/x-patch" (8202 bytes)