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 7FDA7C369B2 for ; Thu, 17 Apr 2025 09:42:03 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1u5LkP-0006eI-PX; Thu, 17 Apr 2025 05:41:29 -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 1u5LkJ-0006bV-Hv for qemu-devel@nongnu.org; Thu, 17 Apr 2025 05:41:25 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1u5LkF-0007oz-AH for qemu-devel@nongnu.org; Thu, 17 Apr 2025 05:41:23 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1744882877; h=from:from:reply-to: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=NFvO6IoBTjWYPf3Ebu5SIXQTPn3yrfwiURlOzjpikzQ=; b=jWbos/bicyn6xbBb7HWBO9DahV8GAgecaOO8X3ytfbGTIIcAU7gKtRWzIVDarkS2pRDzDo KtdCteTMGHwV0qRhSF53k/8X4owX/bxnwE5aTJmoKoXUN6uUbYJggbKKpXYIEJJ9NdTrCE 0OE7RqjEyf3TWytOnF+rHHIyuOWcqcg= Received: from mx-prod-mc-02.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-613-Fz5ei7yjNjqCKdwe3dDzBA-1; Thu, 17 Apr 2025 05:41:15 -0400 X-MC-Unique: Fz5ei7yjNjqCKdwe3dDzBA-1 X-Mimecast-MFC-AGG-ID: Fz5ei7yjNjqCKdwe3dDzBA_1744882874 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (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 mx-prod-mc-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 768351956087; Thu, 17 Apr 2025 09:41:14 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.151]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 37C5A1954B00; Thu, 17 Apr 2025 09:41:12 +0000 (UTC) Date: Thu, 17 Apr 2025 10:41:10 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Yuri Nesterov Cc: qemu-devel@nongnu.org Subject: Re: [PATCH] usb-host: enable autoscan for bus+addr to survive host suspend/resume Message-ID: References: <20250416161929.2846102-1-yuri.nesterov@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.2.13 (2024-03-09) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@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_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Wed, Apr 16, 2025 at 10:27:54PM +0300, Yuri Nesterov wrote: > On Wed, Apr 16, 2025 at 8:07 PM Daniel P. Berrangé wrote: > > > > On Wed, Apr 16, 2025 at 07:19:29PM +0300, Yuri Nesterov wrote: > > > Currently, there is a special case for usb-host devices added using the > > > hostbus= and hostaddr= properties to avoid adding them to the hotplug > > > watchlist, since the address changes every time the device is plugged > > > in. However, on Linux, when the host system goes into suspend and then > > > resumes, those devices stop working in both the guest and the host. > > > > > > Enabling autoscan and adding those devices to the watchlist allows them > > > to keep working in the guest after host suspend/resume. > > > > So IIUC what you're saying is that on suspend the host device > > is removed by the kernel, and on resume, the USB device is > > recreated. So QEMU's open file handle for the USB device is > > invalid after resume. > > > > If the /dev/bus/usb/NNN/NNN file goes away and then gets > > re-created by the kernel though, we can't assume QEMU is > > going to be able to re-open the new /dev/bus/usb device > > file though. > > I'm not sure if the file actually goes away. It looks like the internal > state of the device changes and QEMU receives a "no device" > response in usb_host_req_complete_data. However, the file > remains in place. At least I don't see any changes in udevadm > monitor or inotifywait aside from attribute modifications. > > After resuming from suspend, the device doesn't work on either > host or guest. Probably the device stays with a detached kernel > driver since QEMU can't reattach it after receiving the "no device" > error. Adding such devices to the hotplug watchlist causes QEMU > to reopen them the same way it does for devices specified by > vendorid and productid or hostport. This is a bit odd, as AFAICT from reading the code, the usb_host_auto_check wll only trigger close + re-open of the device, if there is a period of time in which the /dev/bus/usb device node does not exist, but you're saying it remains existing across suspend/resume. > > The reason bus+addr devices aren't currently added to that list is well > explained in commit e058fa2dd599ccc780d334558be9c1d155222b80. > A special case was made because the device address changes every > time it's replugged. However, it turns out that it doesn't change after > a suspend/resume cycle so adding them to the list allows them to > keep working after resume. > With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|