From nobody Mon Feb 9 16:51:16 2026 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.zoho.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; Return-Path: Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) by mx.zohomail.com with SMTPS id 1490986545627119.55782488451996; Fri, 31 Mar 2017 11:55:45 -0700 (PDT) Received: from localhost ([::1]:42466 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cu1i4-0003zl-9x for importer@patchew.org; Fri, 31 Mar 2017 14:55:44 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:42034) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cu1gV-0002zB-Cq for qemu-devel@nongnu.org; Fri, 31 Mar 2017 14:54:10 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cu1gU-00071Y-Gz for qemu-devel@nongnu.org; Fri, 31 Mar 2017 14:54:07 -0400 Received: from mx1.redhat.com ([209.132.183.28]:40000) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1cu1gS-0006zl-0w; Fri, 31 Mar 2017 14:54:04 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 03C4D3E9; Fri, 31 Mar 2017 18:54:03 +0000 (UTC) Received: from red.redhat.com (ovpn-122-200.rdu2.redhat.com [10.10.122.200]) by smtp.corp.redhat.com (Postfix) with ESMTP id 38E5B4FA21; Fri, 31 Mar 2017 18:54:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 03C4D3E9 Authentication-Results: ext-mx05.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx05.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=eblake@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com 03C4D3E9 From: Eric Blake To: qemu-devel@nongnu.org Date: Fri, 31 Mar 2017 13:53:55 -0500 Message-Id: <20170331185356.2479-3-eblake@redhat.com> In-Reply-To: <20170331185356.2479-1-eblake@redhat.com> References: <20170331185356.2479-1-eblake@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Fri, 31 Mar 2017 18:54:03 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PATCH v8 2/3] qcow2: Discard unaligned tail when wiping image 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-block@nongnu.org, mreitz@redhat.com 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" There is a subtle difference between the fast (qcow2v3 with no extra data) and slow path (qcow2v2 format [aka 0.10], or when a snapshot is present) of qcow2_make_empty(). The slow path fails to discard the final (partial) cluster of an unaligned image. The problem stems from the fact that qcow2_discard_clusters() was silently ignoring sub-cluster head and tail on unaligned requests. A quick audit of all callers shows that qcow2_snapshot_create() has always passed a cluster-aligned request since the call was added in commit 1ebf561; qcow2_co_pdiscard() has passed a cluster-aligned request since commit ecdbead taught the block layer about preferred discard alignment; and qcow2_make_empty() was fixed to pass an aligned start (but not necessarily end) in commit a3e1505. Asserting that the start is always aligned also points out that we now have a dead check: rounding the end offset down can never result in a value less than the aligned start offset (the check was rendered dead with commit ecdbead). Meanwhile, we do not want to round the end cluster down in the one case of the end offset matching the (unaligned) file size - that final partial cluster should still be discarded. With those fixes in place, the fast and slow paths are back in sync at discarding an entire image; the next patch will update qemu-iotests to ensure we don't regress. Note that bdrv_co_pdiscard ignores ALL partial cluster requests, including the partial cluster at the end of an image; it can be argued that the partial cluster at the end should be special-cased so that a guest issuing discard requests at proper alignments everywhere else can likewise empty the entire image. But that optimization is left for another day. Signed-off-by: Eric Blake --- v8: swap patch order v7: new patch --- block/qcow2-cluster.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c index 78c11d4..100398c 100644 --- a/block/qcow2-cluster.c +++ b/block/qcow2-cluster.c @@ -1519,12 +1519,10 @@ int qcow2_discard_clusters(BlockDriverState *bs, ui= nt64_t offset, end_offset =3D offset + (nb_sectors << BDRV_SECTOR_BITS); - /* Round start up and end down */ - offset =3D align_offset(offset, s->cluster_size); - end_offset =3D start_of_cluster(s, end_offset); - - if (offset > end_offset) { - return 0; + /* The caller must cluster-align start; round end down except at EOF */ + assert(QEMU_IS_ALIGNED(offset, s->cluster_size)); + if (end_offset !=3D bs->total_sectors * BDRV_SECTOR_SIZE) { + end_offset =3D start_of_cluster(s, end_offset); } nb_clusters =3D size_to_clusters(s, end_offset - offset); --=20 2.9.3