On 04/02/2014 11:03 AM, Michael S. Tsirkin wrote: > On Wed, Apr 02, 2014 at 10:57:08AM -0400, Vlad Yasevich wrote: >> On 04/02/2014 06:46 AM, Yan Vugenfirer wrote: >>> >>> On Apr 2, 2014, at 11:51 AM, Michael S. Tsirkin <m...@redhat.com> wrote: >>> >>>> On Thu, Nov 21, 2013 at 09:05:51PM -0500, Vlad Yasevich wrote: >>>>> When a link change occurs on a backend (like tap), we currently do >>>>> not propage such change to the nic. As a result, when someone turns >>>>> off a link on a tap device, for instance, then a guest doesn't see >>>>> that change and continues to try to send traffic or run DHCP even >>>>> though the lower-layer is disconnected. This is OK when the network >>>>> is set up as a HUB since the the guest may be connected to other HUB >>>>> ports too, but when it's set up as a netdev, it makes thinkgs worse. >>>>> >>>>> The patch addresses this by setting the peers link down only when the >>>>> peer is not a HUBPORT device. With this patch, in the following config >>>>> -netdev tap,id=net0 -device e1000,mac=XXXXX,netdev=net0 >>>>> when net0 link is turned off, the guest e1000 shows lower-layer link >>>>> down. This allows guests to boot much faster in such configurations. >>>>> With windows guest, it also allows the network to recover properly >>>>> since windows will not configure the link-local IPv4 address, and >>>>> when the link is turned on, the proper address address is configured. >>>>> >>>>> Signed-off-by: Vlad Yasevich <vyase...@redhat.com> >>>>> --- >>>>> net/net.c | 26 +++++++++++++++++--------- >>>>> 1 file changed, 17 insertions(+), 9 deletions(-) >>>>> >>>>> diff --git a/net/net.c b/net/net.c >>>>> index 0a88e68..8a084bf 100644 >>>>> --- a/net/net.c >>>>> +++ b/net/net.c >>>>> @@ -1065,15 +1065,23 @@ void qmp_set_link(const char *name, bool up, >>>>> Error **errp) >>>>> nc->info->link_status_changed(nc); >>>>> } >>>>> >>>>> - /* Notify peer. Don't update peer link status: this makes it >>>>> possible to >>>>> - * disconnect from host network without notifying the guest. >>>>> - * FIXME: is disconnected link status change operation useful? >>>>> - * >>>>> - * Current behaviour is compatible with qemu vlans where there could >>>>> be >>>>> - * multiple clients that can still communicate with each other in >>>>> - * disconnected mode. For now maintain this compatibility. */ >>>> >>>> Hmm this went in without much discussion. >>>> >>>> But before this change went in, it was possible to control link state on >>>> NIC >>>> and on link separately, without guest noticing. >>>> >>>> Why did we decide to drop this functionality? >>> >>> Not sure there was a real need for the patch. >>> >>> On other hand Windows guest will not receive IP address from DHCP server if >>> you start VM with tap link down and then set it to up without toggling link >>> state of the guest device as well. >> >> Same for a linux guest. It a fault scenario. So we either handle >> it by propagating the link event, or we forbid it. Doing neither >> allows for a bad state in common configuration. > > It's how networking works. > If I turn off my router at home I can't get dhcp either.
And you device link will show that it has not carrier. > > We had a way to disable networking at link or at > the router, then removed the ability to turn it > off at the router and I'm asking why. We didn't remove the ability to turn it off at router/switch. We just now propagate carrier loss correctly. In fact, if you have a configuration where the VM is connected to a hub in qemu, turning off the link on the 'tap' connected to the same hub doesn't not change guest state. > >> This patch chose to propagate the event under certain configuration. >> >> -vlad > > So don't do this then. > If you want guest to know that link is down, > put it down on guest side. > > It's that simple. > Sorry, but that's not always possible. The host administrator may not always be vm administrator and without this patch vm administrator has no idea what happened to his network. -vlad > > > >>> >>> Yan. >>> >>>> >>>> >>>> >>>>> - if (nc->peer && nc->peer->info->link_status_changed) { >>>>> - nc->peer->info->link_status_changed(nc->peer); >>>>> + if (nc->peer) { >>>>> + /* Change peer link only if the peer is NIC and then notify peer. >>>>> + * If the peer is a HUBPORT or a backend, we do not change the >>>>> + * link status. >>>>> + * >>>>> + * This behavior is compatible with qemu vlans where there could >>>>> be >>>>> + * multiple clients that can still communicate with each other in >>>>> + * disconnected mode. For now maintain this compatibility. >>>>> + */ >>>>> + if (nc->peer->info->type == NET_CLIENT_OPTIONS_KIND_NIC) { >>>>> + for (i = 0; i < queues; i++) { >>>>> + ncs[i]->peer->link_down = !up; >>>>> + } >>>>> + } >>>>> + if (nc->peer->info->link_status_changed) { >>>>> + nc->peer->info->link_status_changed(nc->peer); >>>>> + } >>>>> } >>>>> } >>>>> >>>>> -- >>>>> 1.8.4.2 >>>>> >>>> >>>