On 04/04/2016 03:07 PM, Jesper Dangaard Brouer wrote:
On Mon, 04 Apr 2016 10:49:09 +0200 Daniel Borkmann <dan...@iogearbox.net> wrote:
On 04/02/2016 03:21 AM, Brenden Blanco wrote:
Add a new bpf prog type that is intended to run in early stages of the
packet rx path. Only minimal packet metadata will be available, hence a new
context type, struct xdp_metadata, is exposed to userspace. So far only
expose the readable packet length, and only in read mode.
The PHYS_DEV name is chosen to represent that the program is meant only
for physical adapters, rather than all netdevs.
While the user visible struct is new, the underlying context must be
implemented as a minimal skb in order for the packet load_* instructions
to work. The skb filled in by the driver must have skb->len, skb->head,
and skb->data set, and skb->data_len == 0.
[...]
Do you plan to support bpf_skb_load_bytes() as well? I like using
this API especially when dealing with larger chunks (>4 bytes) to
load into stack memory, plus content is kept in network byte order.
What about other helpers such as bpf_skb_store_bytes() et al that
work on skbs. Do you intent to reuse them as is and thus populate
the per cpu skb with needed fields (faking linear data), or do you
see larger obstacles that prevent for this?
Argh... maybe the minimal pseudo/fake SKB is the wrong "signal" to send
to users of this API.
The hole idea is that an SKB is NOT allocated yet, and not needed at
this level. If we start supporting calling underlying SKB functions,
then we will end-up in the same place (performance wise).
I'm talking about the current skb-related BPF helper functions we have,
so the question is how much from that code we have we can reuse under
these constraints (obviously things like the tunnel helpers are a different
story) and if that trade-off is acceptable for us. I'm also thinking
that, for example, if you need to parse the packet data anyway for a drop
verdict, you might as well pass some meta data (that is set in the real
skb later on) for those packets that go up the stack.
