Messages in this thread | | | Subject | Re: [PATCH net] veth: xdp: use head instead of hard_start | From | Toshiaki Makita <> | Date | Tue, 31 Mar 2020 14:45:26 +0900 |
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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@huawei.com> 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
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