From patchwork Mon Apr 20 13:32:12 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kevin Wolf X-Patchwork-Id: 11498961 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 2BCED6CA for ; Mon, 20 Apr 2020 13:34:22 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 0192A2070B for ; Mon, 20 Apr 2020 13:34:22 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="bl4i68ji" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0192A2070B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Received: from localhost ([::1]:35722 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jQWZ3-0006TB-0E for patchwork-qemu-devel@patchwork.kernel.org; Mon, 20 Apr 2020 09:34:21 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:60900 helo=eggs1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jQWXl-0004Mq-3s for qemu-devel@nongnu.org; Mon, 20 Apr 2020 09:33:06 -0400 Received: from Debian-exim by eggs1p.gnu.org with spam-scanned (Exim 4.90_1) (envelope-from ) id 1jQWXc-0004he-Uf for qemu-devel@nongnu.org; Mon, 20 Apr 2020 09:32:59 -0400 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:60680 helo=us-smtp-delivery-1.mimecast.com) by eggs1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jQWXc-0004de-D6 for qemu-devel@nongnu.org; Mon, 20 Apr 2020 09:32:52 -0400 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= 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 X-MC-Unique: -Ky8TvMcN5OXy8lUZS39mg-1 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) 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 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+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" 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; } + /* + * 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 because + * then the backing file content would become visible. Instead, zero-fill + * the area where backing file and new area overlap. + * + * Note that if the image has a backing file, but was opened without the + * backing file, taking care of keeping things consistent with that backing + * file is the user's responsibility. + */ + if (new_bytes && bs->backing) { + flags |= BDRV_REQ_ZERO_WRITE; + } + if (drv->bdrv_co_truncate) { if (flags & ~bs->supported_truncate_flags) { error_setg(errp, "Block driver does not support requested flags");