From patchwork Tue Mar 26 13:54:37 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kevin Wolf X-Patchwork-Id: 13604230 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 C4377CD11DD for ; Tue, 26 Mar 2024 13:55:49 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rp7GS-0004A1-Ng; Tue, 26 Mar 2024 09:54:56 -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 1rp7GQ-00048b-Ry for qemu-devel@nongnu.org; Tue, 26 Mar 2024 09:54:54 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rp7GO-0001OI-RD for qemu-devel@nongnu.org; Tue, 26 Mar 2024 09:54:54 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1711461292; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=xxieEArCi0NDQMAtUawPdx+iKrN+HtIvUn0JLn9V9qU=; b=a0GeI/uPNWpY/BNVdC+MlQkjRJjZ3f8dxLzkW3K4hTPdCYCdAeGcwqI5tBOHvOaZNqm4Kb SgiF999WbCXu+RkyxujCaxUkVziVCEgV5NRwDzvfwtyBL/hifWi2WhZbRkSRmgr4skEhVJ jFbD78dcvAm8jkzIROk6rS6rBXSUTMo= 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-142-PBajGdvwPXi0YyzqJ9x8uw-1; Tue, 26 Mar 2024 09:54:50 -0400 X-MC-Unique: PBajGdvwPXi0YyzqJ9x8uw-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (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 5C0488007B5; Tue, 26 Mar 2024 13:54:50 +0000 (UTC) Received: from merkur.fritz.box (unknown [10.39.193.60]) by smtp.corp.redhat.com (Postfix) with ESMTP id A60751121312; Tue, 26 Mar 2024 13:54:49 +0000 (UTC) From: Kevin Wolf To: qemu-block@nongnu.org Cc: kwolf@redhat.com, peter.maydell@linaro.org, qemu-devel@nongnu.org Subject: [PULL 3/6] block/io: accept NULL qiov in bdrv_pad_request Date: Tue, 26 Mar 2024 14:54:37 +0100 Message-ID: <20240326135440.421609-4-kwolf@redhat.com> In-Reply-To: <20240326135440.421609-1-kwolf@redhat.com> References: <20240326135440.421609-1-kwolf@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.3 Received-SPF: pass client-ip=170.10.133.124; envelope-from=kwolf@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=-0.088, 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 From: Stefan Reiter 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(). 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. 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: > ./qemu-img create /tmp/backing.qcow2 -f qcow2 64M -o cluster_size=32768 > ./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=node0,file.driver=file,file.filename=/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 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 Message-ID: <20240322095009.346989-2-f.ebner@proxmox.com> Reviewed-by: Kevin Wolf Reviewed-by: Stefan Hajnoczi Signed-off-by: Kevin Wolf --- block/io.c | 33 ++++++++++++++++++++------------- 1 file changed, 20 insertions(+), 13 deletions(-) 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; } - sliced_iov = qemu_iovec_slice(*qiov, *qiov_offset, *bytes, - &sliced_head, &sliced_tail, - &sliced_niov); - - /* Guaranteed by bdrv_check_request32() */ - assert(*bytes <= SIZE_MAX); - ret = bdrv_create_padded_qiov(bs, pad, sliced_iov, sliced_niov, - sliced_head, *bytes); - if (ret < 0) { - bdrv_padding_finalize(pad); - return ret; + /* + * For prefetching in stream_populate(), no qiov is passed along, because + * only copy-on-read matters. + */ + if (qiov && *qiov) { + sliced_iov = qemu_iovec_slice(*qiov, *qiov_offset, *bytes, + &sliced_head, &sliced_tail, + &sliced_niov); + + /* Guaranteed by bdrv_check_request32() */ + assert(*bytes <= SIZE_MAX); + ret = bdrv_create_padded_qiov(bs, pad, sliced_iov, sliced_niov, + sliced_head, *bytes); + if (ret < 0) { + bdrv_padding_finalize(pad); + return ret; + } + *qiov = &pad->local_qiov; + *qiov_offset = 0; } + *bytes += pad->head + pad->tail; *offset -= pad->head; - *qiov = &pad->local_qiov; - *qiov_offset = 0; if (padded) { *padded = true; }