From patchwork Wed Jan 18 14:59:49 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stefan Hajnoczi X-Patchwork-Id: 136647 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [140.186.70.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 78DABB6F62 for ; Thu, 19 Jan 2012 02:42:13 +1100 (EST) Received: from localhost ([::1]:50597 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RnX0G-0004Gp-Qv for incoming@patchwork.ozlabs.org; Wed, 18 Jan 2012 10:00:44 -0500 Received: from eggs.gnu.org ([140.186.70.92]:44489) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RnWzo-0003tB-MR for qemu-devel@nongnu.org; Wed, 18 Jan 2012 10:00:21 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RnWzh-0002QY-5C for qemu-devel@nongnu.org; Wed, 18 Jan 2012 10:00:16 -0500 Received: from e06smtp13.uk.ibm.com ([195.75.94.109]:53850) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RnWzg-0002QF-Sw for qemu-devel@nongnu.org; Wed, 18 Jan 2012 10:00:09 -0500 Received: from /spool/local by e06smtp13.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 18 Jan 2012 15:00:08 -0000 Received: from d06nrmr1707.portsmouth.uk.ibm.com ([9.149.39.225]) by e06smtp13.uk.ibm.com ([192.168.101.143]) with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted; Wed, 18 Jan 2012 15:00:05 -0000 Received: from d06av05.portsmouth.uk.ibm.com (d06av05.portsmouth.uk.ibm.com [9.149.37.229]) by d06nrmr1707.portsmouth.uk.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id q0IF04Lw2502898 for ; Wed, 18 Jan 2012 15:00:04 GMT Received: from d06av05.portsmouth.uk.ibm.com (loopback [127.0.0.1]) by d06av05.portsmouth.uk.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id q0IF03U1018091 for ; Wed, 18 Jan 2012 08:00:03 -0700 Received: from localhost (sig-9-145-203-19.de.ibm.com [9.145.203.19]) by d06av05.portsmouth.uk.ibm.com (8.14.4/8.13.1/NCO v10.0 AVin) with ESMTP id q0IF03MJ018057; Wed, 18 Jan 2012 08:00:03 -0700 From: Stefan Hajnoczi To: Date: Wed, 18 Jan 2012 14:59:49 +0000 Message-Id: <1326898793-20331-4-git-send-email-stefanha@linux.vnet.ibm.com> X-Mailer: git-send-email 1.7.8.3 In-Reply-To: <1326898793-20331-1-git-send-email-stefanha@linux.vnet.ibm.com> References: <1326898793-20331-1-git-send-email-stefanha@linux.vnet.ibm.com> x-cbid: 12011815-2966-0000-0000-000002F1A02C X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 195.75.94.109 Cc: Kevin Wolf , Stefan Hajnoczi Subject: [Qemu-devel] [PATCH v4 3/6] block: perform zero-detection during copy-on-read X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Copy-on-Read populates the image file with data read from a backing image. In order to avoid bloating the image file when all zeroes are read we should scan the buffer and perform an optimized zero write operation. Signed-off-by: Stefan Hajnoczi --- block.c | 14 +++++++++++--- 1 files changed, 11 insertions(+), 3 deletions(-) diff --git a/block.c b/block.c index c9fa5c1..ae297bb 100644 --- a/block.c +++ b/block.c @@ -1517,6 +1517,7 @@ static int coroutine_fn bdrv_co_do_copy_on_readv(BlockDriverState *bs, */ void *bounce_buffer; + BlockDriver *drv = bs->drv; struct iovec iov; QEMUIOVector bounce_qiov; int64_t cluster_sector_num; @@ -1537,14 +1538,21 @@ static int coroutine_fn bdrv_co_do_copy_on_readv(BlockDriverState *bs, iov.iov_base = bounce_buffer = qemu_blockalign(bs, iov.iov_len); qemu_iovec_init_external(&bounce_qiov, &iov, 1); - ret = bs->drv->bdrv_co_readv(bs, cluster_sector_num, cluster_nb_sectors, - &bounce_qiov); + ret = drv->bdrv_co_readv(bs, cluster_sector_num, cluster_nb_sectors, + &bounce_qiov); if (ret < 0) { goto err; } - ret = bs->drv->bdrv_co_writev(bs, cluster_sector_num, cluster_nb_sectors, + if (drv->bdrv_co_write_zeroes && + buffer_is_zero(bounce_buffer, iov.iov_len)) { + ret = drv->bdrv_co_write_zeroes(bs, cluster_sector_num, + cluster_nb_sectors); + } else { + ret = drv->bdrv_co_writev(bs, cluster_sector_num, cluster_nb_sectors, &bounce_qiov); + } + if (ret < 0) { /* It might be okay to ignore write errors for guest requests. If this * is a deliberate copy-on-read then we don't want to ignore the error.