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

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Date:   Mon, 3 Aug 2020 12:02:18 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     David Howells <dhowells@...hat.com>
Cc:     Ian Kent <raven@...maw.net>,
        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 Fri, Jul 24, 2020 at 1:36 PM David Howells <dhowells@...hat.com> wrote:
>
> Ian Kent <raven@...maw.net> wrote:
>
> > I was wondering about id re-use.
> >
> > Assuming that ids that are returned to the idr db are re-used
> > what would the chance that a recently used id would end up
> > being used?
> >
> > Would that chance increase as ids are consumed and freed over
> > time?
>
> I've added something to deal with that in the fsinfo branch.  I've given each
> mount object and superblock a supplementary 64-bit unique ID that's not likely
> to repeat before we're no longer around to have to worry about it.
>
> fsinfo() then allows you to retrieve them by path or by mount ID.

Shouldn't the notification interface provide the unique ID?

Thanks,
Miklos

>
> So, yes, mnt_id and s_dev are not unique and may be reused very quickly, but
> I'm also providing uniquifiers that you can check.
>
> David
>