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

[Paolo Bonzini]

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