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From: | Christoph Hellwig |
Subject: | Re: [Qemu-devel] [RFC PATCH 06/17] block: use bdrv_{co, aio}_discard for write_zeroes operations |
Date: | Sat, 24 Mar 2012 16:33:07 +0100 |
User-agent: | Mutt/1.5.17 (2007-11-01) |
On Wed, Mar 14, 2012 at 01:49:48PM +0100, Paolo Bonzini wrote: > It does make the distinction. "I don't care" is UNMAP (or WRITE > SAME(16) with the UNMAP bit set); "I want to have zeroes" is WRITE > SAME(10) or WRITE SAME(16) with an all-zero payload. But once the taget sets the unmap zeroes data bit even UNMAP / WRITE SAME with unmap have to zero all blocks touched. Also strictly speaking even the WRITE SAME with unmap requires a payload of zeroes, even if most targets don't bother to check for this.
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