Hi,

some months ago I've sent a patch to the linux kernel list that enabled
notification of network driver link state changes over the netlink
socket. Technically, this has been implemented by a kernel thread that
mirrored dev->state:__LINK_STATE_NO_CARRIER into dev->flags:IFF_RUNNING
and sent netlink messages. Note: The in-kernel-flag IFF_RUNNING is
unused at least since 2.4, it is the LINK_STATE_NO_CARRIER bit that is
seen as RUNNING from user mode.

This was followed by a discussion with Jamal (look at
http://marc.theaimsgroup.com/?t=101751064400001&r=1&w=2), however, it
took ...ahem.. a while until the revised version I attach to this mail.
Don't ask ;-)

I had quite positive feedback from LVS and zebra people, so I tried to
remove most of the objections against the patch.

-Anyway, I wanted to keep the current semantics of
netif_carrier_on()/_off(). The extended states that can be found RFC2863
did not seem to useful to me for linux, mainly because "notPresent" is
already implemented with netif_device_detach()/_attach() and especially
for ethernet drivers there is no real difference between "testing" and
"down".
-Using Ingos workqueue implementation, I removed the need for the first
versions' own kernel thread.
-I changed the simple approach of iterating over all network devices,
now the handler only looks at devices that had an event. This change
also increases compatibility to broken drivers that manipulate
IFF_RUNNING directly, there is a good chance that these drivers will
never generate state notification events. I kept the semantic not to
create a list of events for one device, only the latest state change is
forwarded when the queue is run.

Patch against 2.5.41 is attached for comments, of course with the aim of
kernel inclusion. I have tested it on a UP machine, but hope that I've
got the locking stuff right.

Cheers, Stefan