BPF Berkeley Packet Filter Question

[Julian Elischer]

On 30/12/2015 12:46 PM, Juan Herrera wrote:
> Hello BSD folks,
>
> I am developing a networking application in C and I have a question
> regarding BPF (Berkeley Packet Filters), I will give you an idea of the app
> first,  I need to send a packet from machine A to machine B (any kind of
> packet) so for this I wrote a packet generator application which will send
> a packet to machine B, but before sending the packet I need to append some
> metadata values at the end of the packet, already done, so in machine B I
> have a raw socket listener app ready to receive incoming packets from
> machine A, however I want to implement filtering with BPF on machine B, but
> as my metadata was appended at the end of the packet (have to be at the
> end), I need to read the packet length with(using) Berkeley Packet Filter
> to match a specific field to filter one of the bytes at the end of my
> packet (metadata appended), in other words I need to know the incoming
> packet length to filtered against one of the metadatas fields and be able
> to drop the packet before reaching user space applications(drop it in
> kernel space).
>
> So my question is, Can I use BPF to read the packet length ?
to continue on my previous mail.

you can also use netgraph to do this in several ways as well.
But I'd need more information to be able to explain what to do.

>
> TIA!
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