netdev - Re: [PATCH net-next v2] libbpf: add xsk_ring_prod__nb

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Date:   Wed, 26 Jun 2019 10:30:04 +0200
From:   "Eelco Chaudron" <echaudro@...hat.com>
To:     netdev@...r.kernel.org
Cc:     ast@...nel.org, daniel@...earbox.net, kafai@...com,
        songliubraving@...com, yhs@...com, andrii.nakryiko@...il.com,
        magnus.karlsson@...il.com
Subject: Re: [PATCH net-next v2] libbpf: add xsk_ring_prod__nb_free() function

Please ignore, this was supposed to be bpf-next not net-next :(

On 26 Jun 2019, at 10:27, Eelco Chaudron wrote:

> When an AF_XDP application received X packets, it does not mean X
> frames can be stuffed into the producer ring. To make it easier for
> AF_XDP applications this API allows them to check how many frames can
> be added into the ring.
>
> Signed-off-by: Eelco Chaudron <echaudro@...hat.com>
> ---
>
> v1 -> v2
>  - Renamed xsk_ring_prod__free() to xsk_ring_prod__nb_free()
>  - Add caching so it will only touch global state when needed
>
>  tools/lib/bpf/xsk.h | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/tools/lib/bpf/xsk.h b/tools/lib/bpf/xsk.h
> index 82ea71a0f3ec..6acb81102346 100644
> --- a/tools/lib/bpf/xsk.h
> +++ b/tools/lib/bpf/xsk.h
> @@ -76,11 +76,11 @@ xsk_ring_cons__rx_desc(const struct xsk_ring_cons 
> *rx, __u32 idx)
>  	return &descs[idx & rx->mask];
>  }
>
> -static inline __u32 xsk_prod_nb_free(struct xsk_ring_prod *r, __u32 
> nb)
> +static inline __u32 xsk_prod__nb_free(struct xsk_ring_prod *r, __u32 
> nb)
>  {
>  	__u32 free_entries = r->cached_cons - r->cached_prod;
>
> -	if (free_entries >= nb)
> +	if (free_entries >= nb && nb != 0)
>  		return free_entries;
>
>  	/* Refresh the local tail pointer.
> @@ -110,7 +110,7 @@ static inline __u32 xsk_cons_nb_avail(struct 
> xsk_ring_cons *r, __u32 nb)
>  static inline size_t xsk_ring_prod__reserve(struct xsk_ring_prod 
> *prod,
>  					    size_t nb, __u32 *idx)
>  {
> -	if (xsk_prod_nb_free(prod, nb) < nb)
> +	if (xsk_prod__nb_free(prod, nb) < nb)
>  		return 0;
>
>  	*idx = prod->cached_prod;
> -- 
> 2.20.1