On Wed, Apr 02, 2014 at 01:46:14PM +0300, 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. > > Yan.
So why not toggle the link of the guest device? > > > > > > > >> - 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 > >> > >