Re: [PATCH v8 bpf-next 09/14] bpd: add multi-buffer support to xdp copy helpers

[Vladimir Oltean <olteanv@gmail.com>]

On Thu, Apr 08, 2021 at 02:51:01PM +0200, Lorenzo Bianconi wrote:
> From: Eelco Chaudron <echaudro@redhat.com>
> 
> This patch adds support for multi-buffer for the following helpers:
>   - bpf_xdp_output()
>   - bpf_perf_event_output()
> 
> Signed-off-by: Eelco Chaudron <echaudro@redhat.com>
> Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> ---

Also there is a typo in the commit message: bpd -> bpf.

>  net/core/filter.c                             |  63 ++++++++-
>  .../selftests/bpf/prog_tests/xdp_bpf2bpf.c    | 127 ++++++++++++------
>  .../selftests/bpf/progs/test_xdp_bpf2bpf.c    |   3 +-
>  3 files changed, 149 insertions(+), 44 deletions(-)
> 
> diff --git a/net/core/filter.c b/net/core/filter.c
> index c4eb1392f88e..c00f52ab2532 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -4549,10 +4549,56 @@ static const struct bpf_func_proto bpf_sk_ancestor_cgroup_id_proto = {
>  };
>  #endif
>  
> -static unsigned long bpf_xdp_copy(void *dst_buff, const void *src_buff,
> +static unsigned long bpf_xdp_copy(void *dst_buff, const void *ctx,
>  				  unsigned long off, unsigned long len)
>  {
> -	memcpy(dst_buff, src_buff + off, len);
> +	struct xdp_buff *xdp = (struct xdp_buff *)ctx;

There is no need to cast a void pointer in C.

> +	struct xdp_shared_info *xdp_sinfo;
> +	unsigned long base_len;
> +
> +	if (likely(!xdp->mb)) {
> +		memcpy(dst_buff, xdp->data + off, len);
> +		return 0;
> +	}
> +
> +	base_len = xdp->data_end - xdp->data;

Would a static inline int xdp_buff_head_len() be useful?

> +	xdp_sinfo = xdp_get_shared_info_from_buff(xdp);
> +	do {
> +		const void *src_buff = NULL;
> +		unsigned long copy_len = 0;
> +
> +		if (off < base_len) {
> +			src_buff = xdp->data + off;
> +			copy_len = min(len, base_len - off);
> +		} else {
> +			unsigned long frag_off_total = base_len;
> +			int i;
> +
> +			for (i = 0; i < xdp_sinfo->nr_frags; i++) {
> +				skb_frag_t *frag = &xdp_sinfo->frags[i];
> +				unsigned long frag_len, frag_off;
> +
> +				frag_len = xdp_get_frag_size(frag);
> +				frag_off = off - frag_off_total;
> +				if (frag_off < frag_len) {
> +					src_buff = xdp_get_frag_address(frag) +
> +						   frag_off;
> +					copy_len = min(len,
> +						       frag_len - frag_off);
> +					break;
> +				}
> +				frag_off_total += frag_len;
> +			}
> +		}
> +		if (!src_buff)
> +			break;
> +
> +		memcpy(dst_buff, src_buff, copy_len);
> +		off += copy_len;
> +		len -= copy_len;
> +		dst_buff += copy_len;
> +	} while (len);
> +
>  	return 0;
>  }