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 92EA4C3ABC5 for ; Wed, 7 May 2025 08:46:44 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1uCaPn-0007qZ-3d; Wed, 07 May 2025 04:46:07 -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 1uCaPf-0007qR-JC for qemu-devel@nongnu.org; Wed, 07 May 2025 04:45:59 -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 1uCaPb-0000Nw-5q for qemu-devel@nongnu.org; Wed, 07 May 2025 04:45:57 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1746607552; 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=VX04qeOyFgEd1uyFBFdIgzO06tKo8ZQcWBRhUp8irkY=; b=S5eXi9MHcJiv87TCYF7G/+sIHAneeFvFJqdKGIAcq7/oRQcVZEfGPwNHnmH1beLWGftd2w 141/xhaIenlRmiG0JhFzBs1ZSKevPynPr/AgcXwy5+KRWdaii4u/IYcPGihtZV+5p/iIKs 5qsw+c4rCXjQe4ygB6PSlekJlbSa9Yc= Received: from mx-prod-mc-01.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-218-rytgggROO4aKQJRC12XMcA-1; Wed, 07 May 2025 04:45:50 -0400 X-MC-Unique: rytgggROO4aKQJRC12XMcA-1 X-Mimecast-MFC-AGG-ID: rytgggROO4aKQJRC12XMcA_1746607549 Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (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-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 10E0519560AD; Wed, 7 May 2025 08:45:49 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.63]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id D8F0E19560AF; Wed, 7 May 2025 08:45:47 +0000 (UTC) Date: Wed, 7 May 2025 09:45:44 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: =?utf-8?B?U3TDqXBoYW5l?= Graber Cc: qemu-devel@nongnu.org Subject: Re: [PATCH] hw/usb/network: Remove hardcoded 0x40 prefix Message-ID: References: <20250506164602.3897164-1-stgraber@stgraber.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20250506164602.3897164-1-stgraber@stgraber.org> User-Agent: Mutt/2.2.14 (2025-02-20) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.414, 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 Tue, May 06, 2025 at 12:45:53PM -0400, Stéphane Graber via wrote: > USB NICs have a "40:" prefix hardcoded for all MAC addresses. > > This overrides user-provided configuration and leads to an inconsistent > experience. > > I couldn't find any documented reason (comment or git commits) for this > behavior. It seems like everyone is just expecting the MAC address to be > fully passed through to the guest, but it isn't. > > This is also particularly problematic as the "40:" prefix isn't a > reserved prefix for MAC addresses (IEEE OUI). There are a number of > valid allocations out there which use this prefix, meaning that QEMU may > be causing MAC address conflicts. > > Signed-off-by: Stéphane Graber > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2951 > --- > hw/usb/dev-network.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/hw/usb/dev-network.c b/hw/usb/dev-network.c > index 81cc09dcac..1df2454181 100644 > --- a/hw/usb/dev-network.c > +++ b/hw/usb/dev-network.c > @@ -1383,7 +1383,7 @@ static void usb_net_realize(USBDevice *dev, Error **errp) > qemu_format_nic_info_str(qemu_get_queue(s->nic), s->conf.macaddr.a); > snprintf(s->usbstring_mac, sizeof(s->usbstring_mac), > "%02x%02x%02x%02x%02x%02x", > - 0x40, > + s->conf.macaddr.a[0], > s->conf.macaddr.a[1], > s->conf.macaddr.a[2], > s->conf.macaddr.a[3], To repeat what I said in the ticket, the 0x40 byte originates from when this was first committed to QEMU. We can see the finall accepted patch https://lists.nongnu.org/archive/html/qemu-devel/2008-07/msg00385.html but tracing the history back further, this was *not* in the version of the patches submitted by the original author 2 years earlier: https://lists.nongnu.org/archive/html/qemu-devel/2006-10/msg00339.html There's no explanation of this difference. Could easily be a left-over hack from some debugging attempt that no one noticed until now. It can't have been forcing a specific vendor's prefix, since prefixes are more than 1 byte long. To me, it smells like a debugging hack where someone wanted to see this fixed byte appear, though even that is a bit wierd as you could just set the desired mac as a cli arg. Anyway I can't come up with a justification for keeping this, so Reviewed-by: Daniel P. Berrangé ..unless someone believes we need to tie this change to a machine type version ? 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 :|