Hello,
I am requesting a sanity check on my “driver-level”
bridging approach in this e-mail. Please let me know if you see any
“gotcha’s” in this approach.
Problem:
- I have a single
physical ethernet device on my embedded linux target, and I want to bridge
packets to/from a device across on the other side of a shared memory, that
also processes ethernet data.
- For a variety of
reasons, I can’t use the “brctl addbr” utility
(I’ve tried!), so I’m implementing the bridging functionality
for this specific case, at the driver level.
My approach:
- Modify the existing
ethernet driver by adding some additional code:
- Whenever I receive a
packet on the physical ethernet:
- Just before sending
the skb to the network interface (netif_rx(skb)), also push the packet to
shmem.
- Whenever I send a
packet to the physical ethernet:
- Before pushing the
packet to the physical ethernet device, also push the packet to shared
memory.
- When I receive a
packet from the “shared memory” device:
- Build up two copies
of an skb
- Get the handle to
the network device by doing a dev_get_by_name(“eth0”)
- Push one up to the
netif (netif_rx(skb))
- Push the other
(identical) skb to the physical ethernet device.
- dev_put(“eth0”)
when I’m done.
- I use
netif_stop_queue() and netif_wake_queue() for flow control to the network interface,
but for shmem congestion, I just drop packets (for now), since I
don’t have “easy” queue api’s for flow control handy..
Some questions/concerns I have:
- is there something
in the skb that has “directionality”?
- That is, if I take
and skb that is intended to go to the network interface (e.g.
netif_rx(skb)), and “push” it down to physical device, will
something get usynchronized?
- Or, if I get an skb
from the system (from the hard_start_xmit()), can I “push” it
up again to the netif, or will some “directionality” thing in
the skb make things go out of whack?
- Also, if I push all
these additional created skb’s up to the interface, or down, is
there some “count” between the system netif and the physical
device that may get out of whack, and out of sync?
- Also, is there
something like a “man” pages for the above api’s, and
also skb questions? (other than the source code)? I wasn’t to find
a good man page on the above by few minutes “google”
In any case, I’m already partially along this approach, but I sure
could use any advance warning of potential issues and workarounds!
Thanks again.
Suresh Bhaskaran
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