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Fri, 24 Apr 2020 08:55:11 -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-34-KV6ljlsZN0iydn_GufhnNg-1; Fri, 24 Apr 2020 08:55:08 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A7B53180F109; Fri, 24 Apr 2020 12:55:07 +0000 (UTC) Received: from linux.fritz.box.com (ovpn-114-114.ams2.redhat.com [10.36.114.114]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2EFC66084A; Fri, 24 Apr 2020 12:55:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1587732911; 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=1ocEUSIlpGwj/TGvjKW7k4pUWIviCfkD55ancij1hww=; b=idMzoMefdLL/QmfPcyHuGJQJ9p3Z0VgU4AuNFbq7oLoCkl/0m3QqiWhUoC0M0qXknlKH5f KaPw1BuZmD8zCdQFj9EYwJOrku4+W2OoVhu3I4ZAvKobRENR90m9w9NSaoIg36JdO2Zdoz iHqvcAv7U2+1LdIunUsKbrUWWg4xQow= X-MC-Unique: KV6ljlsZN0iydn_GufhnNg-1 From: Kevin Wolf To: qemu-block@nongnu.org Subject: [PATCH v7 07/10] block: truncate: Don't make backing file data visible Date: Fri, 24 Apr 2020 14:54:45 +0200 Message-Id: <20200424125448.63318-8-kwolf@redhat.com> In-Reply-To: <20200424125448.63318-1-kwolf@redhat.com> References: <20200424125448.63318-1-kwolf@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 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 = 2020/04/24 03:54:07 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.120 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, vsementsov@virtuozzo.com, berto@igalia.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" When extending the size of an image that has a backing file larger than its old size, make sure that the backing file data doesn't become visible in the guest, but the added area is properly zeroed out. Consider the following scenario where the overlay is shorter than its backing file: base.qcow2: AAAAAAAA overlay.qcow2: BBBB When resizing (extending) overlay.qcow2, the new blocks should not stay unallocated and make the additional As from base.qcow2 visible like before this patch, but zeros should be read. A similar case happens with the various variants of a commit job when an intermediate file is short (- for unallocated): base.qcow2: A-A-AAAA mid.qcow2: BB-B top.qcow2: C--C--C- After commit top.qcow2 to mid.qcow2, the following happens: mid.qcow2: CB-C00C0 (correct result) mid.qcow2: CB-C--C- (before this fix) Without the fix, blocks that previously read as zeros on top.qcow2 suddenly turn into A. Signed-off-by: Kevin Wolf Reviewed-by: Vladimir Sementsov-Ogievskiy Reviewed-by: Max Reitz --- block/io.c | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/block/io.c b/block/io.c index 795075954e..a4f9714230 100644 --- a/block/io.c +++ b/block/io.c @@ -3394,6 +3394,31 @@ int coroutine_fn bdrv_co_truncate(BdrvChild *child, = int64_t offset, bool exact, goto out; } =20 + /* + * If the image has a backing file that is large enough that it would + * provide data for the new area, we cannot leave it unallocated becau= se + * then the backing file content would become visible. Instead, zero-f= ill + * the new area. + * + * Note that if the image has a backing file, but was opened without t= he + * backing file, taking care of keeping things consistent with that ba= cking + * file is the user's responsibility. + */ + if (new_bytes && bs->backing) { + int64_t backing_len; + + backing_len =3D bdrv_getlength(backing_bs(bs)); + if (backing_len < 0) { + ret =3D backing_len; + error_setg_errno(errp, -ret, "Could not get backing file size"= ); + goto out; + } + + if (backing_len > old_size) { + flags |=3D BDRV_REQ_ZERO_WRITE; + } + } + if (drv->bdrv_co_truncate) { if (flags & ~bs->supported_truncate_flags) { error_setg(errp, "Block driver does not support requested flag= s"); --=20 2.25.3