From patchwork Fri May 10 16:16:13 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kevin Wolf X-Patchwork-Id: 10939223 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 1AA6E76 for ; Fri, 10 May 2019 16:29:39 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 0B84F28B89 for ; Fri, 10 May 2019 16:29:39 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id F12FE28CC3; Fri, 10 May 2019 16:29:38 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 9F4E128B89 for ; Fri, 10 May 2019 16:29:38 +0000 (UTC) Received: from localhost ([127.0.0.1]:46330 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hP8Ov-00013I-TO for patchwork-qemu-devel@patchwork.kernel.org; Fri, 10 May 2019 12:29:37 -0400 Received: from eggs.gnu.org ([209.51.188.92]:40312) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hP8Cj-0004ZZ-Es for qemu-devel@nongnu.org; Fri, 10 May 2019 12:17:02 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hP8Ch-0000SN-Ha for qemu-devel@nongnu.org; Fri, 10 May 2019 12:17:01 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51802) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hP8Cb-0000HH-OF; Fri, 10 May 2019 12:16:55 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 043003082B46; Fri, 10 May 2019 16:16:53 +0000 (UTC) Received: from linux.fritz.box.com (ovpn-116-183.ams2.redhat.com [10.36.116.183]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1F81518504; Fri, 10 May 2019 16:16:51 +0000 (UTC) From: Kevin Wolf To: qemu-block@nongnu.org Date: Fri, 10 May 2019 18:16:13 +0200 Message-Id: <20190510161614.23236-15-kwolf@redhat.com> In-Reply-To: <20190510161614.23236-1-kwolf@redhat.com> References: <20190510161614.23236-1-kwolf@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.45]); Fri, 10 May 2019 16:16:53 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PULL 14/15] qemu-img: Use zero writes after source backing EOF X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" X-Virus-Scanned: ClamAV using ClamSMTP From: Max Reitz Past the end of the source backing file, we memset() buf_old to zero, so it is clearly easy to use blk_pwrite_zeroes() instead of blk_pwrite() then. Signed-off-by: Max Reitz Reviewed-by: Eric Blake Signed-off-by: Kevin Wolf --- qemu-img.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/qemu-img.c b/qemu-img.c index cfa44b4153..28fba1e7a7 100644 --- a/qemu-img.c +++ b/qemu-img.c @@ -3432,6 +3432,8 @@ static int img_rebase(int argc, char **argv) } for (offset = 0; offset < size; offset += n) { + bool buf_old_is_zero = false; + /* How many bytes can we handle with the next read? */ n = MIN(IO_BUF_SIZE, size - offset); @@ -3452,6 +3454,7 @@ static int img_rebase(int argc, char **argv) */ if (offset >= old_backing_size) { memset(buf_old, 0, n); + buf_old_is_zero = true; } else { if (offset + n > old_backing_size) { n = old_backing_size - offset; @@ -3487,8 +3490,12 @@ static int img_rebase(int argc, char **argv) if (compare_buffers(buf_old + written, buf_new + written, n - written, &pnum)) { - ret = blk_pwrite(blk, offset + written, - buf_old + written, pnum, 0); + if (buf_old_is_zero) { + ret = blk_pwrite_zeroes(blk, offset + written, pnum, 0); + } else { + ret = blk_pwrite(blk, offset + written, + buf_old + written, pnum, 0); + } if (ret < 0) { error_report("Error while writing to COW image: %s", strerror(-ret));