Re: BPF_MISC+BPF_COP and BPF_COPX

[Mindaugas Rasiukevicius <rmind%netbsd.org@localhost>]

Alexander Nasonov <alnsn%yandex.ru@localhost> wrote:
> > Yes, I may want to keep the state in the memory store or pass the
> > arguments through it, since the accumulator might not be enough.
> 
> You have access to a whole packet, why do you need to pass additional
> arguments through the store? I'm worried about introducing tight
> coupling between these two very different environments and adding
> "sugar" for easy interaction is a big step in this direction.

Why is it a problem?  Given that the byte-code and the functions would come
from the same source, some coupling seems natural to me.  It is simplistic
anyway: some already parsed offsets or values could be passed through the
memory store.

> > If you prefer getter
> > and setter to perform a boundary check and enforce uint32_t type, I am
> > fine with that.  Although BPF_MEMWORDS constant and words storing
> > 32-bit values stayed since 80s.. it is not going to change.
> > 
> > However, abusing void * is wrong.  Once bpf_filter(9) is adjusted to
> > take an opaque struct bpf_ctx *, the memory store ought to be moved
> > into it.
> 
> Ah, you plan to generalize scratch memory. It's probably fine but don't
> generalize too many things because people (me at least) want to be able
> to recognize the original bpf and its orignal design.

Well, you suggested getter/setter. :)

> Please note that I allocate scratch memory on the stack in bpfjit.
> If you change scratch memory to be under bpf_ctx, you will need to
> reimplement quite a lot in bpfjit code.

Is it really a lot?  We can waste some cycles and just copy them into the
stack (if there are any initial values).

-- 
Mindaugas