Re: [Qemu-devel] [PATCH] net: Update netdev peer on link change

[Stefan Hajnoczi <stefanha@gmail.com>]

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 <vyasevic@redhat.com>
> ---
>  net/net.c | 26 +++++++++++++++++---------
>  1 file changed, 17 insertions(+), 9 deletions(-)

Merged for QEMU 1.8.  Link state changes can lead to weird bugs so I
don't want to rush this into QEMU 1.7.

Thanks, applied to my net-next tree:
https://github.com/stefanha/qemu/commits/net-next

Stefan