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 X-Spam-Level: X-Spam-Status: No, score=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 26944C4BA24 for ; Thu, 27 Feb 2020 10:04:12 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id E531C24680 for ; Thu, 27 Feb 2020 10:04:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="QM4HMZD0" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E531C24680 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:56414 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1j7G1Y-0002TC-T2 for qemu-devel@archiver.kernel.org; Thu, 27 Feb 2020 05:04:08 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:34889) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1j7Fzy-0000zg-Qw for qemu-devel@nongnu.org; Thu, 27 Feb 2020 05:02:35 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1j7Fzs-0008Ql-62 for qemu-devel@nongnu.org; Thu, 27 Feb 2020 05:02:25 -0500 Received: from us-smtp-2.mimecast.com ([205.139.110.61]:22897 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1j7Fzq-0008JO-6o for qemu-devel@nongnu.org; Thu, 27 Feb 2020 05:02:23 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1582797738; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=yEP0uL/7y5bev94ZxGklPmRsSoskzSTmRapYsEMv4ZA=; b=QM4HMZD0AyLQgBn6UjF0RF6Sw4erSeATXee6ou+tLBABxdYM5d1POzJRTYlVdV864BYg4x n7S1rsGBjvKibOTfPtdZWU91n53fMhU7vP4AVFCCyvcDa4Q0Oj2YqkxYwVVbq8t8TOWtiP C1Vp5SIcDAsZCQ8mmpCB0uIW2MfrVlY= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-488-bRKkmXuiN2GPlvUvfEsdNA-1; Thu, 27 Feb 2020 05:02:17 -0500 X-MC-Unique: bRKkmXuiN2GPlvUvfEsdNA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0AA3B13E5; Thu, 27 Feb 2020 10:02:16 +0000 (UTC) Received: from linux.fritz.box (unknown [10.36.118.7]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3054C8B779; Thu, 27 Feb 2020 10:02:08 +0000 (UTC) Date: Thu, 27 Feb 2020 11:02:06 +0100 From: Kevin Wolf To: Coiby Xu Subject: Re: [PATCH v4 0/5] vhost-user block device backend implementation Message-ID: <20200227100206.GA7493@linux.fritz.box> References: <20200218050711.8133-1-coiby.xu@gmail.com> <20200219163815.GD1085125@stefanha-x1.localdomain> <20200227074114.GB83512@stefanha-x1.localdomain> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.61 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: bharatlkmlkvm@gmail.com, =?iso-8859-1?Q?Marc-Andr=E9?= Lureau , qemu-devel@nongnu.org, Stefan Hajnoczi Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 27.02.2020 um 10:53 hat Coiby Xu geschrieben: > Thank you for reminding me of this socket short read issue! It seems > we still need customized vu_message_read because libvhost-user assumes > we will always get a full-size VhostUserMsg and hasn't taken care of > this short read case. I will improve libvhost-user's vu_message_read > by making it keep reading from socket util getting enough bytes. I > assume short read is a rare case thus introduced performance penalty > would be negligible. In any case, please make sure that we use the QIOChannel functions called from a coroutine in QEMU so that it will never block, but the coroutine can just yield while it's waiting for more bytes. Kevin > On Thu, Feb 27, 2020 at 3:41 PM Stefan Hajnoczi wro= te: > > > > On Wed, Feb 26, 2020 at 11:18:41PM +0800, Coiby Xu wrote: > > > Hi Stefan, > > > > > > Thank you for reviewing my code! > > > > > > I tried to reach you on IRC. But somehow either you missed my message > > > or I missed your reply. So I will reply by email instead. > > > > > > If we use qio_channel_set_aio_fd_handler to monitor G_IO_IN event, > > > i.e. use vu_dispatch as the read handler, then we can re-use > > > vu_message_read. And "removing the blocking recv from libvhost-user" > > > isn't necessary because "the operation of poll() and ppoll() is not > > > affected by the O_NONBLOCK flag" despite that we use > > > qio_channel_set_blocking before calling qio_channel_set_aio_fd_handle= r > > > to make recv non-blocking. > > > > I'm not sure I understand. poll() just says whether the file descripto= r > > is readable. It does not say whether enough bytes are readable :). So > > our callback will be invoked if there is 1 byte ready, but when we try > > to read 20 bytes either it will block (without O_NONBLOCK) or return > > only 1 byte (with O_NONBLOCK). Neither case is okay, so I expect that > > code changes will be necessary. > > > > But please go ahead and send the next revision and I'll take a look. > > > > Stefan >=20 >=20 >=20 > -- > Best regards, > Coiby >=20