From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39053) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UopNU-0006r6-9O for qemu-devel@nongnu.org; Tue, 18 Jun 2013 02:26:56 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UopNR-0000vc-KH for qemu-devel@nongnu.org; Tue, 18 Jun 2013 02:26:52 -0400 Received: from mx1.redhat.com ([209.132.183.28]:3239) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UopNR-0000uM-AA for qemu-devel@nongnu.org; Tue, 18 Jun 2013 02:26:49 -0400 Date: Tue, 18 Jun 2013 09:27:35 +0300 From: "Michael S. Tsirkin" Message-ID: <20130618062735.GC23367@redhat.com> References: <1371476111-4449-1-git-send-email-akong@redhat.com> <1371476111-4449-2-git-send-email-akong@redhat.com> <20130617140018.GA10085@redhat.com> <20130618020558.GA9666@localhost.nay.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130618020558.GA9666@localhost.nay.redhat.com> Subject: Re: [Qemu-devel] [PATCH 1/2] avoid to allcate used macaddr to to new nic List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Amos Kong , aliguori@us.ibm.com, qemu-devel@nongnu.org, stefanha@redhat.com On Tue, Jun 18, 2013 at 10:05:58AM +0800, Fam Zheng wrote: > On Mon, 06/17 17:00, Michael S. Tsirkin wrote: > > On Mon, Jun 17, 2013 at 09:35:10PM +0800, Amos Kong wrote: > > > QEMU allocates macaddr to nic if user doesn't assigne macaddr. > > > But we didn't check if the allocated macaddr is used, it might > > > cause macaddr repeated. > > > > > > # qemu -device e1000,netdev=h1,mac=52:54:00:12:34:56 > > > (qemu) device_add e1000 > > > (qemu) info network > > > e1000.0: index=0,type=nic,model=e1000,macaddr=52:54:00:12:34:56 > > > \ h1: index=0,type=user,net=10.0.2.0,restrict=off > > > e1000.1: index=0,type=nic,model=e1000,macaddr=52:54:00:12:34:56 > > > > > > This patch adds a check in allocating macaddr, reallocate macaddr > > > if it's used by other nic. > > > > > > Signed-off-by: Amos Kong > > > > I'm not sure this is not exactly what was intended in this case. > > Also this ptotects against an unlikely case of mixing > > implicit and explicit addresses, but not against > > a likely case of multiple qemu on same LAN using same MAC. > > IMHO, either way we can do little to protect against collision of > multiple qemu on the same LAN, but at least this patch protects against > repeated MAC address in one qemu instance. Better in some degree. This is a policy, we should not dictate it. Maybe you want same MAC for some reason? > Leaving it to user, and asking for address explictly, absolutely helps, > but makes the interface a bit harder to use: there are still cases user > wants it generated automatically. A user that does not want to know what "MAC" even means is the only one I'm aware of. This is not such a case. > Just wondering if a random one could be better? If we are talking about a guest with multiple NICs, if you generate MACs randomly guest won't know which is which. It also breaks assumptions guests make that MAC is a static property of hardware. E.g. it can force windows re-activation, break resume from suspend etc > -- > Fam