From nobody Tue Nov 4 23:49:20 2025 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) client-ip=208.118.235.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=redhat.com Return-Path: Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) by mx.zohomail.com with SMTPS id 1531480603416612.0784228700448; Fri, 13 Jul 2018 04:16:43 -0700 (PDT) Received: from localhost ([::1]:36529 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fdw42-00075N-6r for importer@patchew.org; Fri, 13 Jul 2018 07:16:42 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43865) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fdw1y-0005lf-8c for qemu-devel@nongnu.org; Fri, 13 Jul 2018 07:14:35 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fdw1x-0002cZ-Bk for qemu-devel@nongnu.org; Fri, 13 Jul 2018 07:14:34 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:35900 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fdw1v-0002au-7p; Fri, 13 Jul 2018 07:14:31 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D341D7DAC8; Fri, 13 Jul 2018 11:14:30 +0000 (UTC) Received: from localhost (ovpn-117-56.ams2.redhat.com [10.36.117.56]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 675302156700; Fri, 13 Jul 2018 11:14:30 +0000 (UTC) From: Max Reitz To: qemu-block@nongnu.org Date: Fri, 13 Jul 2018 13:14:23 +0200 Message-Id: <20180713111424.23670-3-mreitz@redhat.com> In-Reply-To: <20180713111424.23670-1-mreitz@redhat.com> References: <20180713111424.23670-1-mreitz@redhat.com> X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.2]); Fri, 13 Jul 2018 11:14:30 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.2]); Fri, 13 Jul 2018 11:14:30 +0000 (UTC) for IP:'10.11.54.6' DOMAIN:'int-mx06.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'mreitz@redhat.com' RCPT:'' X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 66.187.233.73 Subject: [Qemu-devel] [PATCH 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 , qemu-devel@nongnu.org, Max Reitz Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail: RSF_0 Z_629925259 SPT_0 Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" 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 dd684d8bf0..2552e7dad6 100644 --- a/qemu-img.c +++ b/qemu-img.c @@ -3403,6 +3403,8 @@ 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 @@ -3423,6 +3425,7 @@ 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; @@ -3458,8 +3461,12 @@ 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, p= num, 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 2.17.1