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Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on c

From: ronnie sahlberg
Subject: Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert
Date: Wed, 17 Jul 2013 10:09:21 -0700

On Wed, Jul 17, 2013 at 10:02 AM, Peter Lieven <address@hidden> wrote:
> For Disks we always use read/write16 so i think we Should also use 
> writesame16. Or not?

Sounds good.

> Von meinem iPhone gesendet
> Am 17.07.2013 um 18:31 schrieb ronnie sahlberg <address@hidden>:
>> On Wed, Jul 17, 2013 at 9:27 AM, Paolo Bonzini <address@hidden> wrote:
>>> Il 17/07/2013 17:54, ronnie sahlberg ha scritto:
>>>> I think it is reasonable to assume that IF LBPRZ==1 and IF it is an
>>>> "optimal unmap request" then the blocks will become unmapped and they
>>>> will read back as 0.
>>> Yes, but it is not reasonable to assume that bdrv_discard will only
>>> receive "optimal" requests.  Thus, using WRITE SAME for LBPRZ=1, and not
>>> exposing LBPRZ=1 if LBPWS=0 (may also use LBPWS10 depending on the
>>> capacity), is the safer thing to do.
>>> Paolo
>> ACK.
>> WRITESAME10/16 with UNMAP flag set is probably best.

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