linux-kernel - Re: [PATCH 13/17] watch_queue: Implement mount topology and attribute change notifications [ver #5]

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Message-ID: <303106be4785135446e56cb606138a6e94885887.camel@themaw.net>
Date:   Mon, 03 Aug 2020 20:01:27 +0800
From:   Ian Kent <raven@...maw.net>
To:     David Howells <dhowells@...hat.com>,
        Miklos Szeredi <miklos@...redi.hu>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        Christian Brauner <christian@...uner.io>, andres@...razel.de,
        Jeff Layton <jlayton@...hat.com>, dray@...hat.com,
        Karel Zak <kzak@...hat.com>, keyrings@...r.kernel.org,
        Linux API <linux-api@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org,
        LSM <linux-security-module@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 13/17] watch_queue: Implement mount topology and
 attribute change notifications [ver #5]

On Mon, 2020-08-03 at 12:49 +0100, David Howells wrote:
> Miklos Szeredi <miklos@...redi.hu> wrote:
> 
> > OTOH mount notification is way smaller and IMO a more mature
> > interface.  So just picking the unique ID patch into this set might
> > make sense.
> 
> But userspace can't retrieve the unique ID without fsinfo() as things
> stand.
> 
> I'm changing it so that the fields are 64-bit, but initialised with
> the
> existing mount ID in the notifications set.  The fsinfo set changes
> that to a
> unique ID.  I'm tempted to make the unique IDs start at UINT_MAX+1 to
> disambiguate them.

Mmm ... so what would I use as a mount id that's not used, like NULL
for strings?

I'm using -1 now but changing this will mean I need something
different.

Could we set aside a mount id that will never be used so it can be
used for this case?

Maybe mount ids should start at 1 instead of zero ...

Ian