VirtualBox network connectivity broken on recent -CURRENT

[Don Lewis]

On  4 Jun, To: mmacy at nextbsd.org wrote:
> On  4 Jun, Matthew Macy wrote:
>> 
>> 
>> 
>>  ---- On Sat, 04 Jun 2016 19:04:42 -0700 Randy Westlund
>>  <rwestlun at gmail.com> wrote ----
>>  > On Fri, Jun 03, 2016 at 05:11:24PM -0700, Don Lewis wrote: 
>>  > > It looks like something changed in -CURRENT to break network 
>>  > > connectivity to VirtualBox guests.  This was last known to work
>>  > > with r299139 (May 6th) and is definitely broken with r301229.
>>  >  
>>  > I've been having VirtualBox networking problems as well.  I can't
>>  > get my VMs on the network recently, but I don't recall when it
>>  > last worked. Everything looks right from the guest (the arp cache
>>  > shows the VirtualBox NAT router), but tcpdump on the host shows no
>>  > traffic.  I haven't had time to investigate further :/
>>  > 
>> 
>> The odds of it being fixed will increase greatly if someone would do a
>> bisect and test.
> 
> I started bisecting a bit earlier today.  So far all I know is r300184
> is also broken.

The culprit turned out to be r300043.  There seems to be some
sort of ABI compatiblity issue that was resolved when I rebuilt and
reinstalled virtualbox-ose-kmod.  There should probably be note in
src/UPDATING if so.  The .kmod files that I had been
running were probably built with r299139.

I used to have PORTS_MODULES=emulators/virtualbox-ose-kmod in
/etc/make.conf, but took it out because pkg would also try to
intall/upgrade it from my local pkg repo.

What is strange is that the kmods would successfully load even on very
recent kernels, but when I did a "pkg install -f virtualbox-ose-kmod"
to fetch a recently rebuilt version (just a few days old), it would not
load with a r300043 kernel.  Is there a check to prevent a module with a
newer version from loading on an older kernel, but not the reverse?