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 B07D7C74A5B for ; Sat, 18 Mar 2023 12:20:01 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pdVX3-0003l7-KS; Sat, 18 Mar 2023 08:19:33 -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 1pdVX1-0003km-M9 for qemu-devel@nongnu.org; Sat, 18 Mar 2023 08:19:31 -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 1pdVX0-0004Xf-0o for qemu-devel@nongnu.org; Sat, 18 Mar 2023 08:19:31 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1679141965; 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=Ahi+AcoB0aF6LDB17KrdGfGHs2mE9naerJyr3aQJ1CM=; b=jQYiD4CldAK88zs5gnnvpdFYKbR92nwx7kgHpjorKK+qRDVvtqTPly62wSQq7VoFsxW9Sd leHt8TRuskyZ0C6DaaMbdbUnyzRD7337bsTo+P+56IWEFFDW+yGE3BhZEHrb86e6t+SeYn TiAmMvug0oFAzPM8GTa2GkcLCLSwVTo= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-644-UzwqILy_OZWqQueVIO3zXg-1; Sat, 18 Mar 2023 08:19:24 -0400 X-MC-Unique: UzwqILy_OZWqQueVIO3zXg-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 53DFF101A54F; Sat, 18 Mar 2023 12:19:23 +0000 (UTC) Received: from redhat.com (unknown [10.2.16.99]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 656C2C15BAD; Sat, 18 Mar 2023 12:19:22 +0000 (UTC) Date: Sat, 18 Mar 2023 07:19:20 -0500 From: Eric Blake To: Hanna Czenczek Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org, Vladimir Sementsov-Ogievskiy , Kevin Wolf , Stefan Hajnoczi , Fam Zheng Subject: Re: [PATCH 2/4] block: Split padded I/O vectors exceeding IOV_MAX Message-ID: <20230318121920.3pibvzhi47s56zbm@redhat.com> References: <20230317175019.10857-1-hreitz@redhat.com> <20230317175019.10857-3-hreitz@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230317175019.10857-3-hreitz@redhat.com> User-Agent: NeoMutt/20220429 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Received-SPF: pass client-ip=170.10.133.124; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H2=-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 On Fri, Mar 17, 2023 at 06:50:17PM +0100, Hanna Czenczek wrote: > When processing vectored guest requests that are not aligned to the > storage request alignment, we pad them by adding head and/or tail > buffers for a read-modify-write cycle. > > > To do this, the use of qemu_iovec_init_extended() in bdrv_pad_request() > is effectively replaced by the new function bdrv_create_padded_qiov(), > which not only wraps the request IOV with padding head/tail, but also > ensures that the resulting vector will not have more than IOV_MAX > elements. Putting that functionality into qemu_iovec_init_extended() is > infeasible because it requires allocating a bounce buffer; doing so > would require many more parameters (buffer alignment, how to initialize > the buffer, and out parameters like the buffer, its length, and the > original elements), which is not reasonable. > > Conversely, it is not difficult to move qemu_iovec_init_extended()'s > functionality into bdrv_create_padded_qiov() by using public > qemu_iovec_* functions, so that is what this patch does. > > Because bdrv_pad_request() was the only "serious" user of > qemu_iovec_init_extended(), the next patch will remove the latter > function, so the functionality is not implemented twice. > > Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2141964 > Signed-off-by: Hanna Czenczek > --- > block/io.c | 153 +++++++++++++++++++++++++++++++++++++++++++++++++---- > 1 file changed, 143 insertions(+), 10 deletions(-) Reviewed-by: Eric Blake -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org