From nobody Mon Nov 10 15:59:43 2025 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; 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 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=redhat.com ARC-Seal: i=1; a=rsa-sha256; t=1557324243; cv=none; d=zoho.com; s=zohoarc; b=foPZL7/AjLuvbCHpBcUUCUN4bvujxk0f7nA5B9lfGA3IwyWa5XhML0zJe+dG+QRpu3ewiOCkuaxaPqLsbLtJKC2bLR9+d9G0912de3a0rtxKjiFT3s0W4qqjK7y3E+b22kFQ3JflyKlmAQlmgEH4apXn9ZlZXsebyrhbcsJhaBo= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zoho.com; s=zohoarc; t=1557324243; h=Content-Transfer-Encoding:Cc:Date:From:In-Reply-To:List-Subscribe:List-Post:List-Id:List-Archive:List-Help:List-Unsubscribe:MIME-Version:Message-ID:References:Sender:Subject:To:ARC-Authentication-Results; bh=G1UZblFwvw8wiT0kmsvRSAbgexoq2OMGwQdpyaxWY+U=; b=ifPXh2ciDgwJ2rSbj567Of0v0ZkHrDSFxHaVVxfEcgcNAl7cjnFh0RABSXVJcBiS9oxow8yxZr432MkP07zUUzR+/uHcNNGo9TL1V7beMtmQjIKQISuqJOyo1fo8U/983t2kzTG6jGIg8z8bwWEhCnLQhPRJ15JzuTIZIj7Z1yc= ARC-Authentication-Results: i=1; mx.zoho.com; spf=pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail header.from= (p=none dis=none) header.from= Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 15573242435081014.1103515751181; Wed, 8 May 2019 07:04:03 -0700 (PDT) Received: from localhost ([127.0.0.1]:37767 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hONAt-0007wY-Og for importer@patchew.org; Wed, 08 May 2019 10:03:59 -0400 Received: from eggs.gnu.org ([209.51.188.92]:45815) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hON8w-0006Yt-4t for qemu-devel@nongnu.org; Wed, 08 May 2019 10:01:59 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hON8v-00021m-6d for qemu-devel@nongnu.org; Wed, 08 May 2019 10:01:58 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43176) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hON8s-0001uo-NG; Wed, 08 May 2019 10:01:54 -0400 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 529ECC067C19; Wed, 8 May 2019 14:01:46 +0000 (UTC) Received: from localhost (ovpn-204-94.brq.redhat.com [10.40.204.94]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E024E60C74; Wed, 8 May 2019 14:01:45 +0000 (UTC) From: Max Reitz To: qemu-block@nongnu.org Date: Wed, 8 May 2019 16:01:38 +0200 Message-Id: <20190508140139.32722-3-mreitz@redhat.com> In-Reply-To: <20190508140139.32722-1-mreitz@redhat.com> References: <20190508140139.32722-1-mreitz@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Wed, 08 May 2019 14:01:46 +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 v2 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+importer=patchew.org@nongnu.org Sender: "Qemu-devel" 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 e22a4fda17..cfad922816 100644 --- a/qemu-img.c +++ b/qemu-img.c @@ -3431,6 +3431,8 @@ 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 @@ -3451,6 +3453,7 @@ 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; @@ -3486,8 +3489,12 @@ 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 2.20.1