Re: [RFC 1/2] netvsc: reference counting fix

From: Stephen Hemminger <stephen@networkplumber.org>
Date: Sat, 13 Aug 2016 11:35:59 -0700

This is how I think it should be fixed, but not tested yet.

Subjec: netvsc: use device not module reference counts

Fix how the cross-device reference counting is handled.  When VF is
associated with the synthetic interface, the VF driver module should
still be able to be unloaded.  The module unload code will callback
with NETDEV_UNREGISTER event which breaks the connection safely.
(Fixes 9f4b5ba5db4 hv_netvsc: Implement support for VF drivers on Hyper-V)

Signed-off-by: Stephen Hemminger <redacted>

This might not work.

It is assumed that when a netdev unregister happens, it may be done so
at any point in time.

Therefore that NETDEV_UNREGISTER event must eliminate any and all
references to a given netdev.  And that works perfectly fine right now
with all existing subsystems that take references to netdevs.

You'll have to add something so that a NETDEV_UNREGISTER event tears
this VF down and thus releases it's reference to the synthetic device.