linux-kernel - Re: [PATCH] nbd: provide a way for userspace processes to identify device backends

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Message-ID: <CAFnufp3ZzrKHiV1Vy9_bAymy0oEr288dL4yWo4EjqUzhJV6J-A@mail.gmail.com>
Date:   Wed, 19 May 2021 16:33:19 +0200
From:   Matteo Croce <mcroce@...ux.microsoft.com>
To:     Prasanna Kalever <pkalever@...hat.com>
Cc:     Ming Lei <ming.lei@...hat.com>,
        Prasanna Kumar Kalever <prasanna.kalever@...hat.com>,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        nbd@...er.debian.org, Josef Bacik <josef@...icpanda.com>,
        Jens Axboe <axboe@...nel.dk>,
        Ilya Dryomov <idryomov@...hat.com>,
        Xiubo Li <xiubli@...hat.com>,
        Lennart Poettering <lennart@...ttering.net>,
        Luca Boccassi <bluca@...ian.org>
Subject: Re: [PATCH] nbd: provide a way for userspace processes to identify
 device backends

On Tue, May 18, 2021 at 9:52 AM Prasanna Kalever <pkalever@...hat.com> wrote:
> > BTW, loop has similar issue, and patch of 'block: add a sequence number to disks'
> > is added for addressing this issue, what do you think of that generic
> > approach wrt. this nbd's issue? such as used the exposed sysfs sequence number
> > for addressing this issue?
> >
> > https://lore.kernel.org/linux-block/YH81n34d2G3C4Re+@gardel-login/#r
>
> If I understand the changes and the background of the fix correctly, I
> think with that fix author is trying to monotonically increase the seq
> number and add it to the disk on every single device map/attach and
> expose it through the sysfs, which will help the userspace processes
> further to correlate events for particular and specific devices that
> reuse the same loop device.
>

Yes, but nothing prevents to use diskseq in nbd, and increase it on reconfigure.
That would allow to detect if the device has been reconfigured.

Regards,
-- 
per aspera ad upstream