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Date:   Thu, 3 Sep 2020 23:24:09 +0200
From:   Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org, davem@...emloft.net,
        lorenzo.bianconi@...hat.com, brouer@...hat.com,
        echaudro@...hat.com, sameehj@...zon.com, kuba@...nel.org,
        john.fastabend@...il.com, daniel@...earbox.net, ast@...nel.org,
        shayagr@...zon.com
Subject: Re: [PATCH v2 net-next 7/9] bpf: helpers: add multibuffer support

On Thu, Sep 03, 2020 at 10:58:51PM +0200, Lorenzo Bianconi wrote:
> From: Sameeh Jubran <sameehj@...zon.com>
> 
> The implementation is based on this [0] draft by Jesper D. Brouer.
> 
> Provided two new helpers:
> 
> * bpf_xdp_get_frag_count()
> * bpf_xdp_get_frags_total_size()
> 
> [0] xdp mb design - https://github.com/xdp-project/xdp-project/blob/master/areas/core/xdp-multi-buffer01-design.org
> Signed-off-by: Sameeh Jubran <sameehj@...zon.com>
> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> ---
>  include/uapi/linux/bpf.h       | 14 ++++++++++++
>  net/core/filter.c              | 39 ++++++++++++++++++++++++++++++++++
>  tools/include/uapi/linux/bpf.h | 14 ++++++++++++
>  3 files changed, 67 insertions(+)
> 
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index c4a6d245619c..53db75095306 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -3590,6 +3590,18 @@ union bpf_attr {
>   *
>   *	Return
>   *		0 on success, or a negative error in case of failure.
> + *
> + * int bpf_xdp_get_frag_count(struct xdp_buff *xdp_md)
> + *	Description
> + *		Get the total number of frags for a given packet.
> + *	Return
> + *		The number of frags
> + *
> + * int bpf_xdp_get_frags_total_size(struct xdp_buff *xdp_md)
> + *	Description
> + *		Get the total size of frags for a given packet.
> + *	Return
> + *		The total size of frags for a given packet.
>   */
>  #define __BPF_FUNC_MAPPER(FN)		\
>  	FN(unspec),			\
> @@ -3742,6 +3754,8 @@ union bpf_attr {
>  	FN(d_path),			\
>  	FN(copy_from_user),		\
>  	FN(xdp_adjust_mb_header),	\
> +	FN(xdp_get_frag_count),		\
> +	FN(xdp_get_frags_total_size),	\
>  	/* */
>  
>  /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> diff --git a/net/core/filter.c b/net/core/filter.c
> index ae6b10cf062d..ba058fc16440 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -3526,6 +3526,41 @@ static const struct bpf_func_proto bpf_xdp_adjust_mb_header_proto = {
>  	.arg2_type	= ARG_ANYTHING,
>  };
>  
> +BPF_CALL_1(bpf_xdp_get_frag_count, struct  xdp_buff*, xdp)
> +{
> +	struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp);
> +
> +	return xdp->mb ? sinfo->nr_frags : 0;
> +}
> +
> +const struct bpf_func_proto bpf_xdp_get_frag_count_proto = {
> +	.func		= bpf_xdp_get_frag_count,
> +	.gpl_only	= false,
> +	.ret_type	= RET_INTEGER,
> +	.arg1_type	= ARG_PTR_TO_CTX,
> +};
> +
> +BPF_CALL_1(bpf_xdp_get_frags_total_size, struct  xdp_buff*, xdp)
> +{
> +	struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp);
> +	int nfrags, i;
> +	int size = 0;
> +
> +	nfrags = xdp->mb ? sinfo->nr_frags : 0;
> +
> +	for (i = 0; i < nfrags && i < MAX_SKB_FRAGS; i++)
> +		size += skb_frag_size(&sinfo->frags[i]);
> +

I only quickly jumped through series and IMHO this helper should be
rewritten/optimized in a way that we bail out as early as possible if
!xdp->mb as the rest of the code on that condition will do nothing and i'm
not sure if compiler would optimize it.


	struct skb_shared_info *sinfo;
	int nfrags, i;
	int size = 0;

	if (!xdp->mb)
		return 0;

	sinfo = xdp_get_shared_info_from_buff(xdp);

	nfrags = min(sinfo->nr_frags, MAX_SKB_FRAGS);

	for (i = 0; i < nfrags; i++)
		size += skb_frag_size(&sinfo->frags[i]);

	return size;

Thoughts?


> +	return size;
> +}
> +
> +const struct bpf_func_proto bpf_xdp_get_frags_total_size_proto = {
> +	.func		= bpf_xdp_get_frags_total_size,
> +	.gpl_only	= false,
> +	.ret_type	= RET_INTEGER,
> +	.arg1_type	= ARG_PTR_TO_CTX,
> +};
> +
>  BPF_CALL_2(bpf_xdp_adjust_tail, struct xdp_buff *, xdp, int, offset)
>  {
>  	void *data_hard_end = xdp_data_hard_end(xdp); /* use xdp->frame_sz */
> @@ -6889,6 +6924,10 @@ xdp_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>  		return &bpf_xdp_adjust_tail_proto;
>  	case BPF_FUNC_xdp_adjust_mb_header:
>  		return &bpf_xdp_adjust_mb_header_proto;
> +	case BPF_FUNC_xdp_get_frag_count:
> +		return &bpf_xdp_get_frag_count_proto;
> +	case BPF_FUNC_xdp_get_frags_total_size:
> +		return &bpf_xdp_get_frags_total_size_proto;
>  	case BPF_FUNC_fib_lookup:
>  		return &bpf_xdp_fib_lookup_proto;
>  #ifdef CONFIG_INET
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 392d52a2ecef..dd4669096cbb 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -3591,6 +3591,18 @@ union bpf_attr {
>   *
>   *	Return
>   *		0 on success, or a negative error in case of failure.
> + *
> + * int bpf_xdp_get_frag_count(struct xdp_buff *xdp_md)
> + *	Description
> + *		Get the total number of frags for a given packet.
> + *	Return
> + *		The number of frags
> + *
> + * int bpf_xdp_get_frags_total_size(struct xdp_buff *xdp_md)
> + *	Description
> + *		Get the total size of frags for a given packet.
> + *	Return
> + *		The total size of frags for a given packet.
>   */
>  #define __BPF_FUNC_MAPPER(FN)		\
>  	FN(unspec),			\
> @@ -3743,6 +3755,8 @@ union bpf_attr {
>  	FN(d_path),			\
>  	FN(copy_from_user),		\
>  	FN(xdp_adjust_mb_header),	\
> +	FN(xdp_get_frag_count),		\
> +	FN(xdp_get_frags_total_size),	\
>  	/* */
>  
>  /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> -- 
> 2.26.2
> 

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