From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:43414)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <pbonzini@redhat.com>) id 1Uzoys-00057r-4j
	for qemu-devel@nongnu.org; Thu, 18 Jul 2013 10:14:56 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <pbonzini@redhat.com>) id 1Uzoyq-0004HK-Kr
	for qemu-devel@nongnu.org; Thu, 18 Jul 2013 10:14:54 -0400
Received: from mx1.redhat.com ([209.132.183.28]:40055)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <pbonzini@redhat.com>) id 1Uzoyq-0004HF-CN
	for qemu-devel@nongnu.org; Thu, 18 Jul 2013 10:14:52 -0400
Message-ID: <51E7F84C.2080705@redhat.com>
Date: Thu, 18 Jul 2013 16:14:36 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
MIME-Version: 1.0
References: <1373885375-13601-5-git-send-email-pl@kamp.de>
	<20130717084648.GD2458@dhcp-200-207.str.redhat.com>
	<51E66ACD.70706@redhat.com>
	<20130717102551.GF2458@dhcp-200-207.str.redhat.com>
	<CAN05THSiKdxONhHboG5a43KSeAZGnpq9=-T1YAKNipPQccDjww@mail.gmail.com>
	<51E6C5FC.1030304@redhat.com>
	<CAN05THSiLVt-cWq8x26Z6kdsAw0tvGf6zMDeJD8tVmZ=jCTSQQ@mail.gmail.com>
	<7C1EEB41-E2B3-4186-9188-379F02E76FF9@kamp.de>
	<51E6CE81.6000400@redhat.com>
	<36C25446-54C7-4D1F-9D8D-E8A3991489BD@kamp.de>
	<20130718092316.GG3582@dhcp-200-207.str.redhat.com>
	<51E7C260.50404@redhat.com> <51E7C707.7010101@kamp.de>
	<51E7C9C4.5010202@redhat.com> <51E7CBC8.1010804@kamp.de>
	<51E7E035.3010702@redhat.com> <51E7EDD0.6050001@kamp.de>
	<CAN05THS-Fm6A2_kjZ0JOgHR9P5Cy_8OZNdv=EozdUUxssY0yAg@mail.gmail.com>
In-Reply-To: <CAN05THS-Fm6A2_kjZ0JOgHR9P5Cy_8OZNdv=EozdUUxssY0yAg@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target
	on convert
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: ronnie sahlberg <ronniesahlberg@gmail.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Peter Lieven <pl@kamp.de>, qemu-devel <qemu-devel@nongnu.org>, Stefan Hajnoczi <stefanha@redhat.com>

Il 18/07/2013 15:55, ronnie sahlberg ha scritto:
>> > bdrv->write_zeroes will use writesame16 and set the unmap flag only if
>> > BDRV_MAY_DISCARD == 1 and BDRV_O_UNMAP == 1 and lbprz == 1.
> When you use WRITESAME16 you can ignore the lbprz flag.
> Just send a WRITESAME16 command with one block of data that is all set to zero.
> If the unmap flag is set and if unmapped blocks read back the same as
> the block you provided (all zero)
> then it will unmap those blocks, where possible.

True, so the unmap flag can be set iff BDRV_MAY_DISCARD == 1.  block.c
can take care of checking BDRV_O_UNMAP.

Paolo

> All other blocks that can not be unmapped, or where unmapped blocks
> will not read back the same, will instead be overwritten by the
> provided all-zero block.
> 
>