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. This patch chose to propagate the event under certain configuration. -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 >>> >> >