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Mon, 20 Jul 2020 09:18:31 -0400 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-152-yoLrkeaKMqaM0alVRgOJMQ-1; Mon, 20 Jul 2020 09:18:27 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9B7948064DD; Mon, 20 Jul 2020 13:18:26 +0000 (UTC) Received: from linux.fritz.box.com (ovpn-114-59.ams2.redhat.com [10.36.114.59]) by smtp.corp.redhat.com (Postfix) with ESMTP id 82C6B7303C; Mon, 20 Jul 2020 13:18:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1595251109; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=pKcGHN9BiCQRQAAgwMmB3i4OhnaN31yh4S3mMqcJVPM=; b=elkxNzqzqTkI96hadefoGHaQsTAIWilVwqKqWsmB8pmOrElx8J+MNa/yWpIWArhUmXLdgP TQRhE5jfPdCSj/Ff7WstDWxW0QxKkZoETljP3YhUsZRinQwCW2eFTqd0BdN9BvsbAgqiZT c65U94/lsHJnx7yqEGIehjNIzzi6/vM= X-MC-Unique: yoLrkeaKMqaM0alVRgOJMQ-1 From: Kevin Wolf To: qemu-block@nongnu.org Subject: [PATCH for-5.1 1/2] qcow2: Implement v2 zero writes with discard if possible Date: Mon, 20 Jul 2020 15:18:09 +0200 Message-Id: <20200720131810.177978-2-kwolf@redhat.com> In-Reply-To: <20200720131810.177978-1-kwolf@redhat.com> References: <20200720131810.177978-1-kwolf@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.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; Received-SPF: pass client-ip=205.139.110.120; envelope-from=kwolf@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/20 02:11:17 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, nsoffer@redhat.com, qemu-devel@nongnu.org, mreitz@redhat.com Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) Content-Type: text/plain; charset="utf-8" qcow2 version 2 images don't support the zero flag for clusters, so for write_zeroes requests, we return -ENOTSUP and get explicit zero buffer writes. If the image doesn't have a backing file, we can do better: Just discard the respective clusters. This is relevant for 'qemu-img convert -O qcow2 -n', where qemu-img has to assume that the existing target image may contain any data, so it has to write zeroes. Without this patch, this results in a fully allocated target image, even if the source image was empty. Reported-by: Nir Soffer Signed-off-by: Kevin Wolf Reviewed-by: Max Reitz --- block/qcow2-cluster.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c index 4b5fc8c4a7..a677ba9f5c 100644 --- a/block/qcow2-cluster.c +++ b/block/qcow2-cluster.c @@ -1797,8 +1797,15 @@ int qcow2_cluster_zeroize(BlockDriverState *bs, uint= 64_t offset, assert(QEMU_IS_ALIGNED(end_offset, s->cluster_size) || end_offset >=3D bs->total_sectors << BDRV_SECTOR_BITS); =20 - /* The zero flag is only supported by version 3 and newer */ + /* + * The zero flag is only supported by version 3 and newer. However, if= we + * have no backing file, we can resort to discard in version 2. + */ if (s->qcow_version < 3) { + if (!bs->backing) { + return qcow2_cluster_discard(bs, offset, bytes, + QCOW2_DISCARD_REQUEST, false); + } return -ENOTSUP; } =20 --=20 2.25.4