netdev - [PATCH bpf-next v2] libbpf: add xsk_ring_prod__nb

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Message-Id: <d4692ea57ba7a3fe33549fc6222fb8aea5a4225e.1561537968.git.echaudro@redhat.com>
Date:   Wed, 26 Jun 2019 10:33:16 +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: [PATCH bpf-next v2] libbpf: add xsk_ring_prod__nb_free() function

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