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=-2.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 17FD0C54E4B for ; Mon, 11 May 2020 10:21:37 +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 D82022075E for ; Mon, 11 May 2020 10:21:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Wdw4SXGv" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D82022075E 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]:40482 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jY5Z2-0002Au-1t for qemu-devel@archiver.kernel.org; Mon, 11 May 2020 06:21:36 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:48244) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jY5YM-0001Tr-5l for qemu-devel@nongnu.org; Mon, 11 May 2020 06:20:54 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:52601 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jY5YL-0003SS-BT for qemu-devel@nongnu.org; Mon, 11 May 2020 06:20:53 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1589192451; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=VjmQHhVMcUm20e38DUZZKfoXauzZsIWn3wSRQEQWl7Y=; b=Wdw4SXGvwGSpJc6HCLLJ7a8n6v3EzbhQDxVCqOfGB5jtTtGCvGhoXJXr3PaI4x2FB0Cy0Z W32+xl/gecNWhyUEZIMCshR7xkqqybAbxs8zBca6ByVlbOBrtefR9xsx5EI+RrqiPQyQ/Z i6mcF/F+CfPcqsANuEp4m+5jcuVXib0= 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-372-jZ1eBfpYNQSfbWgK7i2CSw-1; Mon, 11 May 2020 06:20:49 -0400 X-MC-Unique: jZ1eBfpYNQSfbWgK7i2CSw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 27848107ACCA for ; Mon, 11 May 2020 10:20:49 +0000 (UTC) Received: from [10.40.192.119] (unknown [10.40.192.119]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 62B3F1002394; Mon, 11 May 2020 10:20:43 +0000 (UTC) Subject: Re: device hotplug & file handles To: Gerd Hoffmann , libvir-list@redhat.com, qemu-devel@nongnu.org References: <20200507144914.4zg3753uh3kytz6g@sirius.home.kraxel.org> From: Michal Privoznik Message-ID: Date: Mon, 11 May 2020 12:20:41 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200507144914.4zg3753uh3kytz6g@sirius.home.kraxel.org> Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=205.139.110.61; envelope-from=mprivozn@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/11 03:10:56 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] 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_PASS=-0.001 autolearn=_AUTOLEARN 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 5/7/20 4:49 PM, Gerd Hoffmann wrote: > Hi, > > For usb device pass-through (aka -device usb-host) it would be very > useful to pass file handles from libvirt to qemu. The workflow would > change from ... > > (1) libvirt enables access to /dev/usb/$bus/$dev > (2) libvirt passes $bus + $dev (using hostbus + hostaddr properties) > to qemu. > (3) qemu opens /dev/usb/$bus/$dev > > ... to ... > > (1) libvirt opens /dev/usb/$bus/$dev > (2) libvirt passes filehandle to qemu. > > Question is how can we pass the file descriptor best? My idea would be > to simply add an fd property to usb-host: > > * Coldplug would be "-device usb-host,fd=" (cmd line). > * Hotplug would be "device_add usb-host,fd=" (monitor). > > Will that work from libvirt point of view? > Or does anyone have an better idea? > > thanks, > Gerd > > PS: background: https://bugzilla.redhat.com/show_bug.cgi?id=1595525 > I don't have a better idea, but a little background on why libvirt even invented private /dev in the first place. The reason was that occasionally, when udev ran its rules it would overwrite the security labels on /dev nodes set by libvirt and thus denying access to QEMU. See: https://bugzilla.redhat.com/show_bug.cgi?id=1354251 Now, I think there is the same risk with what you are proposing. This isn't problem for DAC where permissions are checked during open(), but it may be a problem for SELinux where each individual operation with the FD is inspected. Having said that, I am not against this approach, in fact I'm in favour of it. Let's hope that people learned that having udev overwriting seclabels is a bad idea and the bug won't appear again. Michal