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

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert
Date: Wed, 17 Jul 2013 18:27:40 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130625 Thunderbird/17.0.7

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.


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