From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ian Kent <raven@themaw.net>
Date: Mon, 03 Aug 2020 12:01:27 +0000
Subject: Re: [PATCH 13/17] watch_queue: Implement mount topology and attribute change notifications [ver #5]
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To: David Howells <dhowells@redhat.com>, Miklos Szeredi <miklos@szeredi.hu>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, Al Viro <viro@zeniv.linux.org.uk>, Casey Schaufler <casey@schaufler-ca.com>, Stephen Smalley <sds@tycho.nsa.gov>, Nicolas Dichtel <nicolas.dichtel@6wind.com>, Christian Brauner <christian@brauner.io>, andres@anarazel.de, Jeff Layton <jlayton@redhat.com>, dray@redhat.com, Karel Zak <kzak@redhat.com>, keyrings@vger.kernel.org, Linux API <linux-api@vger.kernel.org>, linux-fsdevel@vger.kernel.org, LSM <linux-security-module@vger.kernel.org>, linux-kernel@vger.kernel.org

On Mon, 2020-08-03 at 12:49 +0100, David Howells wrote:
> Miklos Szeredi <miklos@szeredi.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