linux-kernel - Re: [PATCH 3/7] vfs: Add a mount-notification facility

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Message-ID: <CAG48ez2SAKbPeChAf06GMazMPPThFM+OR00abRZafAP7v+ptKw@mail.gmail.com>
Date:   Wed, 29 May 2019 01:23:36 +0200
From:   Jann Horn <jannh@...gle.com>
To:     David Howells <dhowells@...hat.com>
Cc:     Al Viro <viro@...iv.linux.org.uk>, raven@...maw.net,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        linux-block@...r.kernel.org, keyrings@...r.kernel.org,
        linux-security-module <linux-security-module@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/7] vfs: Add a mount-notification facility

On Wed, May 29, 2019 at 1:04 AM David Howells <dhowells@...hat.com> wrote:
> Jann Horn <jannh@...gle.com> wrote:
> > It might make sense to redesign this stuff so that watches don't hold
> > references on the object being watched.
>
> I explicitly made it hold a reference so that if you place a watch on an
> automounted mount it stops it from expiring.
>
> Further, if I create a watch on something, *should* it be unmountable, just as
> if I had a file open there or had chdir'd into there?

I don't really know. I guess it depends on how it's being used? If
someone decides to e.g. make a file browser that installs watches for
a bunch of mountpoints for some fancy sidebar showing the device
mounts on the system, or something like that, that probably shouldn't
inhibit unmounting... I don't know if that's a realistic use case.