From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EDA4EC04AB2 for ; Thu, 9 May 2019 17:54:41 +0000 (UTC) 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.kernel.org (Postfix) with ESMTPS id C646C2085A for ; Thu, 9 May 2019 17:54:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C646C2085A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([127.0.0.1]:58810 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hOnFh-0003ri-2R for qemu-devel@archiver.kernel.org; Thu, 09 May 2019 13:54:41 -0400 Received: from eggs.gnu.org ([209.51.188.92]:34746) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hOnDs-0002kv-Sw for qemu-devel@nongnu.org; Thu, 09 May 2019 13:52:49 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hOnDr-0006Dt-Rz for qemu-devel@nongnu.org; Thu, 09 May 2019 13:52:48 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34186) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hOnDo-0006CF-NC; Thu, 09 May 2019 13:52:44 -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 13433C05683E; Thu, 9 May 2019 17:52:44 +0000 (UTC) Received: from localhost (ovpn-204-168.brq.redhat.com [10.40.204.168]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A122A19C77; Thu, 9 May 2019 17:52:43 +0000 (UTC) From: Max Reitz To: qemu-block@nongnu.org Date: Thu, 9 May 2019 19:52:36 +0200 Message-Id: <20190509175237.19363-3-mreitz@redhat.com> In-Reply-To: <20190509175237.19363-1-mreitz@redhat.com> References: <20190509175237.19363-1-mreitz@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 [10.5.110.32]); Thu, 09 May 2019 17:52:44 +0000 (UTC) Content-Transfer-Encoding: quoted-printable 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] [PATCH v3 2/3] 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: Kevin Wolf , Vladimir Sementsov-Ogievskiy , qemu-devel@nongnu.org, Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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 --- 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) } =20 for (offset =3D 0; offset < size; offset +=3D n) { + bool buf_old_is_zero =3D false; + /* How many bytes can we handle with the next read? */ n =3D MIN(IO_BUF_SIZE, size - offset); =20 @@ -3452,6 +3454,7 @@ static int img_rebase(int argc, char **argv) */ if (offset >=3D old_backing_size) { memset(buf_old, 0, n); + buf_old_is_zero =3D true; } else { if (offset + n > old_backing_size) { n =3D 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 =3D blk_pwrite(blk, offset + written, - buf_old + written, pnum, 0); + if (buf_old_is_zero) { + ret =3D blk_pwrite_zeroes(blk, offset + written,= pnum, 0); + } else { + ret =3D blk_pwrite(blk, offset + written, + buf_old + written, pnum, 0); + } if (ret < 0) { error_report("Error while writing to COW image: = %s", strerror(-ret)); --=20 2.21.0