On 2020/03/31 12:56, maowenan wrote:
On 2020/3/31 7:35, Toshiaki Makita wrote:
Hi Mao & Jesper
(Resending with plain text...)
On 2020/03/30 20:34, Jesper Dangaard Brouer wrote:
On Mon, 30 Mar 2020 18:26:31 +0800
Mao Wenan <maowenan@xxxxxxxxxx> wrote:
xdp.data_hard_start is mapped to the first
address of xdp_frame, but the pointer hard_start
is the offset(sizeof(struct xdp_frame)) of xdp_frame,
it should use head instead of hard_start to
set xdp.data_hard_start. Otherwise, if BPF program
calls helper_function such as bpf_xdp_adjust_head, it
will be confused for xdp_frame_end.
I have noticed this[1] and have a patch in my current patchset for
fixing this. IMHO is is not so important fix right now, as the effect
is that you currently only lose 32 bytes of headroom.
I consider that it is needed because bpf_xdp_adjust_head() just a common helper function,
veth as one driver application should keep the same as 32 bytes of headroom as other driver.
And convert_to_xdp_frame set() also store info in top of packet, and set:
xdp_frame = xdp->data_hard_start;
[1] https://lore.kernel.org/netdev/158446621887.702578.17234304084556809684.stgit@firesoul/
You are right, the subtraction is not necessary here.
I guess you mean that previous subtraction is not necessary ? this line : void *head = hard_start - sizeof(struct xdp_frame); ?
No I just mean subtraction of headroom is not necessary, and I noticed this
description was confusing. Sorry about that.
You can use "head" for data_hard_start.
Toshiaki Makita
