From nobody Mon Feb 9 15:10:29 2026 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.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; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=redhat.com ARC-Seal: i=1; a=rsa-sha256; t=1557870265; cv=none; d=zoho.com; s=zohoarc; b=WrbW1TT8ROLtb4tFvJRGnsl6MtjHxjc78d3vMF/PWvejL6CV2VZijngz9jRe7OLSHv6CdYPozIwjpVUxeILSBMMzBH8XjIFVKCt5fbqeMpIGLCaVQ45U8Ji5U0cR3KBmMqeetSFC/WaCmkHDwUy1MdKYOuMMuLkfWKz9JCt6c5w= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zoho.com; s=zohoarc; t=1557870265; h=Content-Transfer-Encoding:Cc:Date:From:In-Reply-To:List-Subscribe:List-Post:List-Id:List-Archive:List-Help:List-Unsubscribe:MIME-Version:Message-ID:References:Sender:Subject:To:ARC-Authentication-Results; bh=c8Eu4lF/1AsSB8wLMxlRWLMe1eeBc4H+rZHjPxC72+M=; b=Zw+i0u8zojUti1UOYx5Av78vP9lJatfBcM8tcUd0ItxYfK4SUmpuiaxtxmeIMf8sz9eM8VFc43rr41sxZyWObIE+vLvQ9rnZIYeKCnky6ITrW2UAcG/psUeLj390gcL3u/QCSAvv34P2v2r6ta43viI1CMJT258bJOSf7tqP+R4= ARC-Authentication-Results: i=1; mx.zoho.com; spf=pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail header.from= (p=none dis=none) header.from= Return-Path: Received: from lists.gnu.org (209.51.188.17 [209.51.188.17]) by mx.zohomail.com with SMTPS id 1557870265799308.59166339608066; Tue, 14 May 2019 14:44:25 -0700 (PDT) Received: from localhost ([127.0.0.1]:55055 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hQfDc-0000ln-Ja for importer@patchew.org; Tue, 14 May 2019 17:44:16 -0400 Received: from eggs.gnu.org ([209.51.188.92]:49304) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hQfC6-0008Ix-6R for qemu-devel@nongnu.org; Tue, 14 May 2019 17:42:43 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hQfC4-0006qC-UO for qemu-devel@nongnu.org; Tue, 14 May 2019 17:42:42 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34428) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hQfC1-0006f7-0i; Tue, 14 May 2019 17:42:37 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id EE42036955; Tue, 14 May 2019 21:42:35 +0000 (UTC) Received: from localhost (unknown [10.40.205.236]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7F2795C236; Tue, 14 May 2019 21:42:35 +0000 (UTC) From: Max Reitz To: qemu-block@nongnu.org Date: Tue, 14 May 2019 23:42:29 +0200 Message-Id: <20190514214230.22601-2-mreitz@redhat.com> In-Reply-To: <20190514214230.22601-1-mreitz@redhat.com> References: <20190514214230.22601-1-mreitz@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Tue, 14 May 2019 21:42:36 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PATCH 1/2] block/file-posix: Unaligned O_DIRECT block-status 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: Kevin Wolf , qemu-stable@nongnu.org, qemu-devel@nongnu.org, Max Reitz Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" Content-Type: text/plain; charset="utf-8" Currently, qemu crashes whenever someone queries the block status of an unaligned image tail of an O_DIRECT image: $ echo > foo $ qemu-img map --image-opts driver=3Dfile,filename=3Dfoo,cache.direct=3Don Offset Length Mapped to File qemu-img: block/io.c:2093: bdrv_co_block_status: Assertion `*pnum && QEMU_IS_ALIGNED(*pnum, align) && align > offset - aligned_offset' failed. This is because bdrv_co_block_status() checks that the result returned by the driver's implementation is aligned to the request_alignment, but file-posix can fail to do so, which is actually mentioned in a comment there: "[...] possibly including a partial sector at EOF". Fix this by rounding up those partial sectors. There are two possible alternative fixes: (1) We could refuse to open unaligned image files with O_DIRECT altogether. That sounds reasonable until you realize that qcow2 does necessarily not fill up its metadata clusters, and that nobody runs qemu-img create with O_DIRECT. Therefore, unpreallocated qcow2 files usually have an unaligned image tail. (2) bdrv_co_block_status() could ignore unaligned tails. It actually throws away everything past the EOF already, so that sounds reasonable. Unfortunately, the block layer knows file lengths only with a granularity of BDRV_SECTOR_SIZE, so bdrv_co_block_status() usually would have to guess whether its file length information is inexact or whether the driver is broken. Fixing what raw_co_block_status() returns is the safest thing to do. There seems to be no other block driver that sets request_alignment and does not make sure that it always returns aligned values. Cc: qemu-stable@nongnu.org Signed-off-by: Max Reitz Reviewed-by: Eric Blake --- block/file-posix.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/block/file-posix.c b/block/file-posix.c index e09e15bbf8..f489a5420c 100644 --- a/block/file-posix.c +++ b/block/file-posix.c @@ -2488,6 +2488,9 @@ static int coroutine_fn raw_co_block_status(BlockDriv= erState *bs, off_t data =3D 0, hole =3D 0; int ret; =20 + assert(QEMU_IS_ALIGNED(offset, bs->bl.request_alignment) && + QEMU_IS_ALIGNED(bytes, bs->bl.request_alignment)); + ret =3D fd_open(bs); if (ret < 0) { return ret; @@ -2513,6 +2516,20 @@ static int coroutine_fn raw_co_block_status(BlockDri= verState *bs, /* On a data extent, compute bytes to the end of the extent, * possibly including a partial sector at EOF. */ *pnum =3D MIN(bytes, hole - offset); + + /* + * We are not allowed to return partial sectors, though, so + * round up if necessary. + */ + if (!QEMU_IS_ALIGNED(*pnum, bs->bl.request_alignment)) { + int64_t file_length =3D raw_getlength(bs); + if (file_length > 0) { + /* Ignore errors, this is just a safeguard */ + assert(hole =3D=3D file_length); + } + *pnum =3D ROUND_UP(*pnum, bs->bl.request_alignment); + } + ret =3D BDRV_BLOCK_DATA; } else { /* On a hole, compute bytes to the beginning of the next extent. = */ --=20 2.21.0