linux-kernel - Re: [PATCH v2] xen-blkback: fix persistent grants negotiation

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Date:   Fri, 15 Jul 2022 15:46:43 +0000
From:   SeongJae Park <sj@...nel.org>
To:     Andrii Chepurnyi <andrii.chepurnyi82@...il.com>
Cc:     Oleksandr <olekstysh@...il.com>, SeongJae Park <sj@...nel.org>,
        roger.pau@...rix.com, jgross@...e.com, axboe@...nel.dk,
        boris.ostrovsky@...cle.com, mheyne@...zon.de,
        xen-devel@...ts.xenproject.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2] xen-blkback: fix persistent grants negotiation

Hello,


Oleksandr, thank you for Cc-ing Andrii.  Andrii, thank you for the comment!

On Fri, 15 Jul 2022 15:00:10 +0300 Andrii Chepurnyi <andrii.chepurnyi82@...il.com> wrote:

> [-- Attachment #1: Type: text/plain, Size: 5237 bytes --]
> 
> Hello All,
> 
> I faced the mentioned issue recently and just to bring more context here is
> our setup:
> We use pvblock backend for Android guest. It starts using u-boot with
> pvblock support(which frontend doesn't support the persistent grants
> feature), later it loads and starts the Linux kernel(which frontend
> supports the persistent grants feature). So in total, we have sequent two
> different frontends reconnection, the first of which doesn't support
> persistent grants.
> So the original patch [1] perfectly solves the original issue and provides
> the ability to use persistent grants after the reconnection when Linux
> frontend which supports persistent grants comes into play.
> At the same time [2] will disable the persistent grants feature for the
> first and second frontend.

Thank you for this great explanation of your situation.

> Is it possible to keep [1]  as is?

Yes, my concerns about Max's original patch[1] are conflicting behavior
description in the document[1] and different behavior on blkfront-side
'feature_persistent' parameter.  I will post Max's patch again with patches for
blkfront behavior change and Documents updates.

[1] https://lore.kernel.org/xen-devel/20220121102309.27802-1-sj@kernel.org/


Thanks,
SJ

> 
> [1]
> https://lore.kernel.org/xen-devel/20220106091013.126076-1-mheyne@amazon.de/
> [2] https://lore.kernel.org/xen-devel/20220714224410.51147-1-sj@kernel.org/
> 
> Best regards,
> Andrii
> 
> On Fri, Jul 15, 2022 at 1:15 PM Oleksandr <olekstysh@...il.com> wrote:
> 
> >
> > On 15.07.22 01:44, SeongJae Park wrote:
> >
> >
> > Hello all.
> >
> > Adding Andrii Chepurnyi to CC who have played with the use-case which
> > required reconnect recently and faced some issues with
> > feature_persistent handling.
[...]