On Mon, Apr 11, 2016 at 5:04 PM, David Howells <[email protected]> wrote:
> Hi Willem,
>
> With regards to:
>
> commit 4d0fc73ebe94ac984a187f21fbf4f3a1ac846f5a
> Author: Willem de Bruijn <[email protected]>
> Date: Thu Apr 7 11:44:59 2016 -0400
>
> rxrpc: do not pull udp headers on receive
>
> Commit e6afc8ace6dd modified the udp receive path by pulling the udp
> header before queuing an skbuff onto the receive queue.
>
> Does that mean that I can no longer access the UDP header via udp_hdr(skb)
> from with the ->data_ready() handler?
>
> I'm guessing that's not actually the case since ip_hdr(skb) seems to work - or
> is that something I shouldn't be using since the part of the buffer containing
> the IP header might've been discarded?
The network and transport header pointers are still valid. Commit e6afc8ace6dd
only changes where skb->data points to. It does not discard the data between
skb->head and skb->data. This rxrpc follow-up patch fixes some offset
arithmetic to the payload, which is computed relative to skb->data.
There are other uses of ip_hdr and udp_hdr in udp_recvmsg and similar
recvmsg handlers for other protocols. For instance, in the source address
processing for recvfrom ("if (sin) { .. }")
