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Date: Wed, 17 Jul 2013 19:04:01 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target
	on convert
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To: Peter Lieven <pl@kamp.de>
Cc: Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>, qemu-devel <qemu-devel@nongnu.org>, ronnie sahlberg <ronniesahlberg@gmail.com>

Il 17/07/2013 19:02, Peter Lieven ha scritto:
> For Disks we always use read/write16 so i think we Should also use writesame16. Or not?

Yes.

Remember you can still use UNMAP if LBPRZ=0.

Paolo

> Von meinem iPhone gesendet
> 
> Am 17.07.2013 um 18:31 schrieb ronnie sahlberg <ronniesahlberg@gmail.com>:
> 
>> On Wed, Jul 17, 2013 at 9:27 AM, Paolo Bonzini <pbonzini@redhat.com> 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.