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=-4.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 435BCC433E0 for ; Tue, 11 Aug 2020 10:24:11 +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 16F752054F for ; Tue, 11 Aug 2020 10:24:11 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 16F752054F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:42748 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1k5RRy-0005Pt-7m for qemu-devel@archiver.kernel.org; Tue, 11 Aug 2020 06:24:10 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:38704) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1k5RRB-0004za-B3 for qemu-devel@nongnu.org; Tue, 11 Aug 2020 06:23:21 -0400 Received: from mx2.suse.de ([195.135.220.15]:39178) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1k5RR9-00074p-Dg for qemu-devel@nongnu.org; Tue, 11 Aug 2020 06:23:20 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id B7594AE51; Tue, 11 Aug 2020 10:23:36 +0000 (UTC) Message-ID: Subject: Reminder: [PATCH v2] virtio-rng: return available data with O_NONBLOCK From: Martin Wilck To: "Michael S. Tsirkin" , Jason Wang Date: Tue, 11 Aug 2020 12:23:15 +0200 In-Reply-To: <20200715133255.10526-1-mwilck@suse.com> References: <20200715133255.10526-1-mwilck@suse.com> Content-Type: text/plain; charset="ISO-8859-15" User-Agent: Evolution 3.36.4 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=195.135.220.15; envelope-from=mwilck@suse.com; helo=mx2.suse.de X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/11 02:05:49 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x (no timestamps) [generic] X-Spam_score_int: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action 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: qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 2020-07-15 at 15:32 +0200, mwilck@suse.com wrote: > From: Martin Wilck > > If a program opens /dev/hwrng with O_NONBLOCK and uses poll() and > non-blocking read() to retrieve random data, it ends up in a tight > loop with poll() always returning POLLIN and read() returning EAGAIN. > This repeats forever until some process makes a blocking read() call. > The reason is that virtio_read() always returns 0 in non-blocking > mode, > even if data is available. Worse, it fetches random data from the > hypervisor after every non-blocking call, without ever using this > data. Gentle review reminder. https://patchew.org/QEMU/20200715133255.10526-1-mwilck@suse.com/ Regards Martin