On Tue, 26 Aug 2008 19:29:12 -0700
"Suresh Bhaskaran" <Suresh.Bhaskaran@xxxxxxxxxxxxxx> wrote:
> 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
>
>
>
You just reinvented AF_PACKET with mmap. I don't see why you want to.
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