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 E98C8C54E68 for ; Tue, 19 Mar 2024 18:51:54 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rmeYF-0004YD-LY; Tue, 19 Mar 2024 14:51:08 -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 1rmeYB-0004XT-4R for qemu-devel@nongnu.org; Tue, 19 Mar 2024 14:51:03 -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 1rmeY9-0007su-0y for qemu-devel@nongnu.org; Tue, 19 Mar 2024 14:51:02 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1710874259; 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=RSbqtND9/mjwNUd9Dgm2TGpPJGE+aWvOrCqrjJnBnJk=; b=eJgd8wbTdFwsYJRApYzSmVa2sXJKo3CQDxEoHNPAnXGPWTOmUL0zEBx8d9xI5sVgp9AjsM aVpZouAgiTIGhvSDUjh3v8cguUMWe4srAjf2h8wD0qvvmxfkfGKeBSkOMrWaejNk84RPT3 Lnyk2pSlveVQ++y/fePieL0zfUPd32M= 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-307-Cu-hB8kLMG2UF6M8yWdDEA-1; Tue, 19 Mar 2024 14:50:57 -0400 X-MC-Unique: Cu-hB8kLMG2UF6M8yWdDEA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (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 8B89E8007A6; Tue, 19 Mar 2024 18:50:56 +0000 (UTC) Received: from localhost (unknown [10.39.195.82]) by smtp.corp.redhat.com (Postfix) with ESMTP id CA6A63C20; Tue, 19 Mar 2024 18:50:55 +0000 (UTC) Date: Tue, 19 Mar 2024 14:50:34 -0400 From: Stefan Hajnoczi To: Fiona Ebner Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, hreitz@redhat.com, kwolf@redhat.com, fam@euphon.net, t.lamprecht@proxmox.com, w.bumiller@proxmox.com Subject: Re: [PATCH] block/io: accept NULL qiov in bdrv_pad_request Message-ID: <20240319185034.GC1127203@fedora> References: <20240319091341.303414-1-f.ebner@proxmox.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="J9S/dtcBNMOND2p9" Content-Disposition: inline In-Reply-To: <20240319091341.303414-1-f.ebner@proxmox.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.1 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: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.422, 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, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=unavailable 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 --J9S/dtcBNMOND2p9 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Mar 19, 2024 at 10:13:41AM +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 Hi Fiona, Can you add a qemu-iotests test case for this issue? Thanks, Stefan >=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 > --- > block/io.c | 31 +++++++++++++++++++------------ > 1 file changed, 19 insertions(+), 12 deletions(-) >=20 > diff --git a/block/io.c b/block/io.c > index 33150c0359..395bea3bac 100644 > --- a/block/io.c > +++ b/block/io.c > @@ -1726,22 +1726,29 @@ static int bdrv_pad_request(BlockDriverState *bs, > return 0; > } > =20 > - sliced_iov =3D qemu_iovec_slice(*qiov, *qiov_offset, *bytes, > - &sliced_head, &sliced_tail, > - &sliced_niov); > + /* > + * For prefetching in stream_populate(), no qiov is passed along, be= cause > + * only copy-on-read matters. > + */ > + if (qiov && *qiov) { > + sliced_iov =3D qemu_iovec_slice(*qiov, *qiov_offset, *bytes, > + &sliced_head, &sliced_tail, > + &sliced_niov); > =20 > - /* Guaranteed by bdrv_check_request32() */ > - assert(*bytes <=3D SIZE_MAX); > - ret =3D bdrv_create_padded_qiov(bs, pad, sliced_iov, sliced_niov, > - sliced_head, *bytes); > - if (ret < 0) { > - bdrv_padding_finalize(pad); > - return ret; > + /* Guaranteed by bdrv_check_request32() */ > + assert(*bytes <=3D SIZE_MAX); > + ret =3D bdrv_create_padded_qiov(bs, pad, sliced_iov, sliced_niov, > + sliced_head, *bytes); > + if (ret < 0) { > + bdrv_padding_finalize(pad); > + return ret; > + } > + *qiov =3D &pad->local_qiov; > + *qiov_offset =3D 0; > } > + > *bytes +=3D pad->head + pad->tail; > *offset -=3D pad->head; > - *qiov =3D &pad->local_qiov; > - *qiov_offset =3D 0; > if (padded) { > *padded =3D true; > } > --=20 > 2.39.2 >=20 >=20 --J9S/dtcBNMOND2p9 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmX53noACgkQnKSrs4Gr c8iatAf8DP/oO0mZvaGXV8KnpTNaEdnvJYrd5/UHgMca0IiSK7ZWH0YfiHb09w8t vbFIr4hrLzwdpygmAexav01B+J0bdV1jBxBcxYPRoVha2axq2ABUmxhMoROxXfcG EOKlTz0xgnxhmGwQ77/UtltepKzbm+cHmT0+raLNa+R3wLBZxtavZpK8EAqbHkjQ WmT+MToQnE+fGeZkz+3hRuTkoVJJh0Udez/dwgIa3hh0azDQGx4G9Bs47xhA6Kxi FAo0XbgW0mfItim+xDJRbCcEDKedsa7FMKZnNpDj2vLaPYvMvE5Zf1apgVt+/6Vm /PwMQllMiKqe5TcKu53yZL9sAgjBJg== =+b+3 -----END PGP SIGNATURE----- --J9S/dtcBNMOND2p9--