linux-kernel - Re: [Xen-devel] [PATCH 0/2] block/xen-blkfront: Support non-indirect with 64KB page granularity

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Message-ID: <55F5B6BD.4030904@citrix.com>
Date:	Sun, 13 Sep 2015 18:47:41 +0100
From:	Julien Grall <julien.grall@...rix.com>
To:	Bob Liu <bob.liu@...cle.com>
CC:	<xen-devel@...ts.xenproject.org>, <ian.campbell@...rix.com>,
	<stefano.stabellini@...citrix.com>, <linux-kernel@...r.kernel.org>,
	"David Vrabel" <david.vrabel@...rix.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Roger Pau Monné <roger.pau@...rix.com>
Subject: Re: [Xen-devel] [PATCH 0/2] block/xen-blkfront: Support non-indirect
 with 64KB page granularity



On 13/09/2015 13:44, Bob Liu wrote:
> I may misunderstood here.
> But I think same changes are also required even if backend supports indirect grant when frontend is using 64KB page granularity.
> Else
> 1) How to set up the grant map for requests in domU?
> The minimum segment buffer size in a request is PAGE_SIZE(64KB) while grant is 4KB based.
>
> 2) Codes like below in blkback.c may not work correctly?
> if ((req->u.rw.seg[i].last_sect >= (PAGE_SIZE >> 9)) ||
>
> Because PAGE_SIZE in backend is 4KB, while the written value by domU is 64KB based.

As mention in my cover letter, this patch is not self-sufficient to 
support 64KB guest. It's a follow-up of the 64KB page granularity 
support I sent on the ML (the new version was sent earlier this week [1]).

One of the patch [2] is taking care of breaking down the I/O request in 
multiple 4KB segment that will be used in the ring request. You may want 
to give a look to this patch before looking to this series.

Regards,

[1] https://lwn.net/Articles/656797/
[2] http://www.spinics.net/lists/arm-kernel/msg430468.html

-- 
Julien Grall
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