Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley
        Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United
        Kingdom.
        Registered in England and Wales under Company Registration No. 3798903
From:   David Howells <dhowells@redhat.com>
In-Reply-To: <303106be4785135446e56cb606138a6e94885887.camel@themaw.net>
References: <303106be4785135446e56cb606138a6e94885887.camel@themaw.net> <CAJfpeguO8Qwkzx9zfGVT7W+pT5p6fgj-_8oJqJbXX_KQBpLLEQ@mail.gmail.com> <1293241.1595501326@warthog.procyon.org.uk> <CAJfpegspWA6oUtdcYvYF=3fij=Bnq03b8VMbU9RNMKc+zzjbag@mail.gmail.com> <158454378820.2863966.10496767254293183123.stgit@warthog.procyon.org.uk> <158454391302.2863966.1884682840541676280.stgit@warthog.procyon.org.uk> <2003787.1595585999@warthog.procyon.org.uk> <865566fb800a014868a9a7e36a00a14430efb11e.camel@themaw.net> <2023286.1595590563@warthog.procyon.org.uk> <CAJfpegsT_3YqHPWCZGX7Lr+sE0NVmczWz5L6cN8CzsVz4YKLCQ@mail.gmail.com> <1283475.1596449889@warthog.procyon.org.uk> <1576646.1596455376@warthog.procyon.org.uk>
To:     Ian Kent <raven@themaw.net>
Cc:     dhowells@redhat.com, Miklos Szeredi <miklos@szeredi.hu>,
        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
Subject: Re: [PATCH 13/17] watch_queue: Implement mount topology and attribute change notifications [ver #5]
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <1692825.1596457912.1@warthog.procyon.org.uk>
Date:   Mon, 03 Aug 2020 13:31:52 +0100
Message-ID: <1692826.1596457912@warthog.procyon.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Ian Kent <raven@themaw.net> wrote:

> > 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?

Zero is skipped, so you could use that.

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

It's 64-bits, so you're not likely to see it reach -1, even if it does start
at UINT_MAX+1.

David