netdev - Re: [PATCH bpf-next v3] libbpf: add xsk_ring_prod__nb

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Date:   Fri, 5 Jul 2019 16:35:29 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Eelco Chaudron <echaudro@...hat.com>, netdev@...r.kernel.org
Cc:     ast@...nel.org, kafai@...com, songliubraving@...com, yhs@...com,
        andrii.nakryiko@...il.com, magnus.karlsson@...il.com
Subject: Re: [PATCH bpf-next v3] libbpf: add xsk_ring_prod__nb_free() function

On 07/03/2019 02:52 PM, 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>

The commit log as it is along with the code is a bit too confusing for
readers. After all you only do a rename below. It would need to additionally
state that the rename is as per libbpf convention (xyz__ prefix) in order to
denote that this API is exposed to be used by applications.

Given you are doing this for xsk_prod_nb_free(), should we do the same for
xsk_cons_nb_avail() as well? Extending XDP sample app would be reasonable
addition as well in this context.

> ---
> 
> v2 -> v3
>  - Removed cache by pass option
> 
> 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 | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/lib/bpf/xsk.h b/tools/lib/bpf/xsk.h
> index 82ea71a0f3ec..3411556e04d9 100644
> --- a/tools/lib/bpf/xsk.h
> +++ b/tools/lib/bpf/xsk.h
> @@ -76,7 +76,7 @@ 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;
>  
> @@ -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;
>