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

[Peter Lieven]

For Disks we always use read/write16 so i think we Should also use writesame16. 
Or not?

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.