From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org 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 smtp.lore.kernel.org (Postfix) with ESMTPS id B8C06C54E64 for ; Mon, 25 Mar 2024 19:57:45 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1roqRH-0007jY-HC; Mon, 25 Mar 2024 15:57:00 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1roqRA-0007iv-K1 for qemu-devel@nongnu.org; Mon, 25 Mar 2024 15:56:52 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1roqR9-0005k4-1l for qemu-devel@nongnu.org; Mon, 25 Mar 2024 15:56:52 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1711396609; 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: in-reply-to:in-reply-to:references:references; bh=7WYCJ/fs5qtm0lfmnlO1gUKlf4Od1iU5/JbvJs425q4=; b=BKrce+owaU4KmvQwf/R4XykksXHBiJuXNZ1buDCOYWrnZeG+omjmj2M2mtA6nfWXtLVfrq XVXChMfDQIgmeJE4DSdhDedFFC5IzCs3NF/yFs6iMqazp6fRWZ/+3gMhFdcyH+4vObZGfC xjMCuYJeom+yimgJOovEwanYDHsM0mg= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-563-Tz6ZBPMGNdy4zZ1tDXSThQ-1; Mon, 25 Mar 2024 15:56:45 -0400 X-MC-Unique: Tz6ZBPMGNdy4zZ1tDXSThQ-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 4A9D88FA220; Mon, 25 Mar 2024 19:56:45 +0000 (UTC) Received: from localhost (unknown [10.39.192.114]) by smtp.corp.redhat.com (Postfix) with ESMTP id 71159492BD0; Mon, 25 Mar 2024 19:56:44 +0000 (UTC) Date: Mon, 25 Mar 2024 15:56:38 -0400 From: Stefan Hajnoczi To: Fiona Ebner Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, qemu-stable@nongnu.org, hreitz@redhat.com, kwolf@redhat.com, fam@euphon.net, t.lamprecht@proxmox.com, w.bumiller@proxmox.com Subject: Re: [PATCH v3 1/4] block/io: accept NULL qiov in bdrv_pad_request Message-ID: <20240325195638.GA1944176@fedora> References: <20240322095009.346989-1-f.ebner@proxmox.com> <20240322095009.346989-2-f.ebner@proxmox.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="GPYy9dBDu50Ywqcl" Content-Disposition: inline In-Reply-To: <20240322095009.346989-2-f.ebner@proxmox.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.10 Received-SPF: pass client-ip=170.10.129.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.065, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org --GPYy9dBDu50Ywqcl Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, Mar 22, 2024 at 10:50:06AM +0100, Fiona Ebner wrote: > From: Stefan Reiter >=20 > Some operations, e.g. block-stream, perform reads while discarding the > results (only copy-on-read matters). In this case, they will pass NULL > as the target QEMUIOVector, which will however trip bdrv_pad_request, > since it wants to extend its passed vector. In particular, this is the > case for the blk_co_preadv() call in stream_populate(). >=20 > If there is no qiov, no operation can be done with it, but the bytes > and offset still need to be updated, so the subsequent aligned read > will actually be aligned and not run into an assertion failure. >=20 > In particular, this can happen when the request alignment of the top > node is larger than the allocated part of the bottom node, in which > case padding becomes necessary. For example: >=20 > > ./qemu-img create /tmp/backing.qcow2 -f qcow2 64M -o cluster_size=3D327= 68 > > ./qemu-io -c "write -P42 0x0 0x1" /tmp/backing.qcow2 > > ./qemu-img create /tmp/top.qcow2 -f qcow2 64M -b /tmp/backing.qcow2 -F = qcow2 > > ./qemu-system-x86_64 --qmp stdio \ > > --blockdev qcow2,node-name=3Dnode0,file.driver=3Dfile,file.filename=3D/= tmp/top.qcow2 \ > > < > {"execute": "qmp_capabilities"} > > {"execute": "blockdev-add", "arguments": { "driver": "compress", "file"= : "node0", "node-name": "node1" } } > > {"execute": "block-stream", "arguments": { "job-id": "stream0", "device= ": "node1" } } > > EOF >=20 > Originally-by: Stefan Reiter > Signed-off-by: Thomas Lamprecht > [FE: do update bytes and offset in any case > add reproducer to commit message] > Signed-off-by: Fiona Ebner > --- >=20 > No changes in v3. > No changes in v2. >=20 > block/io.c | 31 +++++++++++++++++++------------ > 1 file changed, 19 insertions(+), 12 deletions(-) Reviewed-by: Stefan Hajnoczi --GPYy9dBDu50Ywqcl Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmYB1vYACgkQnKSrs4Gr c8g6gQgAurkX9/v/rP6xPV0XPQZpnL/T2sM688MOA3UAhg2QjdYyfsU79mbAZ7pe TNHDMfiYtOlfjp4qgK6GfPfTlbTPig6H2finN+PCM044txIexy2qfBzUmjIqhOzt 6fvJDiggcRu5VuH8aCWwPc6Mzld1YgZ1YBLryo33mb6F6ImaMRorSUu3p1pkMZkm bOn/aE3uuRjMTFiaqVvYCXLxT+pn8jGcAfCOdcAL3PtWQHPyt3MjKfyBf0+8u1Jm pPyrQ1tH+g/EeW4kNS0GX1JOo3B/1PzuxSWOXRnfwwRHp35XqdAD6QWhzpi0ybcX Q9bQgKIBb7O77PPEf1T326AyICto1Q== =E78V -----END PGP SIGNATURE----- --GPYy9dBDu50Ywqcl--