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Mon, 20 Apr 2020 09:32:52 -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-285--Ky8TvMcN5OXy8lUZS39mg-1; Mon, 20 Apr 2020 09:32:47 -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 00CAA802570; Mon, 20 Apr 2020 13:32:46 +0000 (UTC) Received: from linux.fritz.box.com (ovpn-114-38.ams2.redhat.com [10.36.114.38]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7A8CF116D9F; Mon, 20 Apr 2020 13:32:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1587389569; 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=jcer1LVMtRqjIwUaiSpHPGpJOhvpyU4IPvZZtPti7wU=; b=bl4i68jiOLrp0/5CnKKCZrRGdChYkeIwPXxbo+1PrzWTfuGdtMigSm0+o3JQlWLeh8RWV8 xtPcFYliAYXYThNTYt5A7dABCdlfbcxeOIlc7eca9d9Tr4ConhVdaE39JykQAVUndT/qRq VsgfEK9HY72CtRYWfkWjNJtEO30KWSc= X-MC-Unique: -Ky8TvMcN5OXy8lUZS39mg-1 From: Kevin Wolf To: qemu-block@nongnu.org Subject: [PATCH v4 7/9] block: truncate: Don't make backing file data visible Date: Mon, 20 Apr 2020 15:32:12 +0200 Message-Id: <20200420133214.28921-8-kwolf@redhat.com> In-Reply-To: <20200420133214.28921-1-kwolf@redhat.com> References: <20200420133214.28921-1-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=207.211.31.81; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs1p.gnu.org: First seen = 2020/04/20 01:47:04 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.81 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: Alberto Garcia --- block/io.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/block/io.c b/block/io.c index 795075954e..f149dff3ba 100644 --- a/block/io.c +++ b/block/io.c @@ -3394,6 +3394,20 @@ 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 area where backing file and new area overlap. + * + * 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) { + 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 2.20.1