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

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Date:   Wed, 26 May 2021 16:13:23 +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 Wed, May 19, 2021 at 4:33 PM Matteo Croce <mcroce@...ux.microsoft.com> wrote:
>
> 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

FYI: I just sent a v2 of the diskseq change

https://lore.kernel.org/linux-block/20210520135622.44625-1-mcroce@linux.microsoft.com/

-- 
per aspera ad upstream