From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45837) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UzlhK-00069I-MZ for qemu-devel@nongnu.org; Thu, 18 Jul 2013 06:44:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UzlhI-0007dM-3J for qemu-devel@nongnu.org; Thu, 18 Jul 2013 06:44:34 -0400 Received: from mx.ipv6.kamp.de ([2a02:248:0:51::16]:41769 helo=mx01.kamp.de) by eggs.gnu.org with smtp (Exim 4.71) (envelope-from ) id 1UzlhH-0007cy-PC for qemu-devel@nongnu.org; Thu, 18 Jul 2013 06:44:32 -0400 Message-ID: <51E7C707.7010101@kamp.de> Date: Thu, 18 Jul 2013 12:44:23 +0200 From: Peter Lieven 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> <51E6C5FC.1030304@redhat.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> In-Reply-To: <51E7C260.50404@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: Kevin Wolf , Stefan Hajnoczi , qemu-devel , ronnie sahlberg On 18.07.2013 12:24, Paolo Bonzini wrote: > Il 18/07/2013 11:23, Kevin Wolf ha scritto: >> Am 17.07.2013 um 19:48 hat Peter Lieven geschrieben: >>> Am 17.07.2013 um 19:04 schrieb Paolo Bonzini : >>> >>>> Il 17/07/2013 19:02, Peter Lieven ha scritto: >>>>> For Disks we always use read/write16 so i think we Should also use writesame16. Or not? >>>> Yes. >>>> >>>> Remember you can still use UNMAP if LBPRZ=0. >>> I can always use it if writesame is not available, but in this case bdi->discard_zeroes must be 0. >>> >>> Maybe we should call it discard_writes_zeroes or similar. >>> >>> Discard_zeroes is sth that should only indicate if lbprz == 1. At least if we refer to the Linux ioctl. We could include both in BDI. >> Maybe what we really should do is to define different operations (with >> an exact behaviour) instead of having one bdrv_discard() and then adding >> flags everywhere to tell what the operation is doing exactly. > A BDRV_MAY_UNMAP flag for bdrv_write_zeroes? I thought that we wanted to add a paramter to the BDI (call it write_zeroes_w_discard). If this is set the bdrv MUST accept a flag to bdrv_discard() lets call it BDRV_DISCARD_WRITE_ZEROES and he has to ensure that all sectors specified in bdrv_discard() read as zero after the operation. If this flag is not set (e.g. when the OS issues a normal discard) the operation may still silently fail with undefined provisioning state and content of the specified sectors. With the above flag a general optimization of bdrv_write_zeroes would be possible, that calls bdrv_discard with BDRV_DISCARD_WRITE_ZEROES if bdi->write_zeroes_w_discard == 1. For iscsi this would mean it sets bdi->write_zeroes_w_discard = 1 iff BDRV_O_UNMAP == 1 and lbpme == 1 and lbpws == 1 and lbprz == 1. The second flag that could be added is bdi->discard_zeroes. But this only says unmapped blocks read back as zero. Peter