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

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Date:   Mon, 03 Aug 2020 13:31:52 +0100
From:   David Howells <dhowells@...hat.com>
To:     Ian Kent <raven@...maw.net>
Cc:     dhowells@...hat.com, Miklos Szeredi <miklos@...redi.hu>,
        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]

Ian Kent <raven@...maw.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