linux-kernel - Re: [Xen-devel] [PATCH v2 2/2] block/xen-blkfront: Handle non-indirect grant with 64KB pages

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Date:	Thu, 12 Nov 2015 18:32:55 +0000
From:	Julien Grall <julien.grall@...rix.com>
To:	Roger Pau Monné <roger.pau@...rix.com>,
	<xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>
CC:	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Ian Campbell <ian.campbell@...rix.com>
Subject: Re: [Xen-devel] [PATCH v2 2/2] block/xen-blkfront: Handle non-indirect
 grant with 64KB pages

On 12/11/15 18:24, Roger Pau Monné wrote:
>> So if one get EOPNOTSUPP the other will get too.
> 
> That's why I said that I think it's not currently possible. IMHO, it's
> fine as it is now.
> 
> The only scenario I can think of that can lead to that combination is
> that we migrate the guest and one request gets processed by one backend
> that supports the operation, while the other request get processed by a
> backend that doesn't support it.
> 
> With your current implementation we would return an error code anyway,
> which is not that bad I guess.

hmmm ... We would return an error to the block layer rather than 0
because the operation is not supported.

That reminds me that blkif_recover needs to be fixed to support
splitting request. I haven't done it because ARM doesn't yet support
suspend/resume (CCing Ian who is working on it).

>>>
>>> Should s->status be able to store all the possible return codes from the
>>> response (OK/ERROR/NOTSUPP)?
>>
>> That could would work. However, how do you decide which will be the
>> final status?
> 
> It should be the most restrictive one, for example if we have ERROR and
> NOTSUPP we should return ERROR, while if we have OK and NOTSUPP we
> should return NOTSUPP.

I will give a look.

-- 
Julien Grall
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