Hi,

For some reason I totally forgot in the process, I thought I needed VLAN
support in uml_switch. I had fun all weekend working on this, and it
actually seems to be working, too. Which is amazing, as in general my C
code doesn't work all that great :-)

So, if you want to play with the kernel's 8021q module which implements
IEEE802.1q VLANs, here's a patch to uml_switch so VLANs stay seperate on
a switch level too.

About this patch:
This patch is against uml_router in uml_utilities_20040406.tar.bz2 and
it adds a -vlan parameter to uml_switch. If -vlan is not used, it should
drop back to default behaviour of switching all packets (did a quick
test, and it seems to do that). The switch itself is still not very
intelligent. In effect it's the connecting UML which decides which VLAN
it wants to be on, and the switch will happily forward packets to ports
which are listed as being on the same VLAN. For this the "port"
structure in port.c has been expanded to hold an extra VLAN ID field
(static int vid). Also, the packet struct has been replaced by a packet
union, which is capable of switching holding either a IEEE 802.1q packet
or a normal packet. The switching functionality itself has been modified
to check for a VLAN match between sender host and receiving port. If no
match can be made, it'll drop the packet silently, else it'll pass it
along to the proper port on which the destination host lives. Also the
TUNTAP interface can now be VLAN'ed to accomodate several separate
chunks of UML network. I tested some scenarios, and it seems to work
fairly well under my tests.

The use:
I have no idea. Maybe it's a useful feature for someone, maybe it's not.
For me it's been primarily playing around so far, though I'm starting to
develop an idea of making an UML based router which is capable of
routing between seperate VLANs with UMLs and from there to the host OS
using only one TUNTAP interface.

Oh, for those who want to play around with this; you'll need a tool to
configure VLANs available in your UML image. It's called `vconfig`, and
can be found, together with a short explanation/howto on:
http://www.candelatech.com/~greear/vlan.html

I'm not a star coder by any definition, so this might in fact be the
ugliest hack you've ever seen. Don't be afraid to let me know about it,
but please also include suggestions on how to make it better.

Enjoy.

-- 
Regards,

Ferdinand O. Tempel

Your friendly neighborhood linuxops.net administrator.