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

[ronnie sahlberg]

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.