netdev - [PATCH bpf 2/2] libbpf: remove dependency on barrier.h in xsk.h

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Date:   Tue,  9 Apr 2019 08:44:13 +0200
From:   Magnus Karlsson <magnus.karlsson@...el.com>
To:     magnus.karlsson@...el.com, bjorn.topel@...el.com, ast@...nel.org,
        daniel@...earbox.net, netdev@...r.kernel.org
Cc:     bpf@...r.kernel.org, bruce.richardson@...el.com,
        ciara.loftus@...el.com, ilias.apalodimas@...aro.org,
        xiaolong.ye@...el.com, ferruh.yigit@...el.com,
        qi.z.zhang@...el.com, georgmueller@....net
Subject: [PATCH bpf 2/2] libbpf: remove dependency on barrier.h in xsk.h

The use of smp_rmb() and smp_wmb() creates a Linux header dependency
on barrier.h that is uneccessary in most parts. This patch implements
the two small defines that are needed from barrier.h. As a bonus, the
new implementations are faster than the default ones as they default
to sfence and lfence for x86, while we only need a compiler barrier in
our case. Just as it is when the same ring access code is compiled in
the kernel.

Fixes: 1cad07884239 ("libbpf: add support for using AF_XDP sockets")
Signed-off-by: Magnus Karlsson <magnus.karlsson@...el.com>
---
 tools/lib/bpf/xsk.h | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/xsk.h b/tools/lib/bpf/xsk.h
index 3638147..317b44f 100644
--- a/tools/lib/bpf/xsk.h
+++ b/tools/lib/bpf/xsk.h
@@ -39,6 +39,21 @@ DEFINE_XSK_RING(xsk_ring_cons);
 struct xsk_umem;
 struct xsk_socket;
 
+#if !defined bpf_smp_rmb && !defined bpf_smp_wmb
+# if defined(__i386__) || defined(__x86_64__)
+#  define bpf_smp_rmb() asm volatile("" : : : "memory")
+#  define bpf_smp_wmb() asm volatile("" : : : "memory")
+# elif defined(__aarch64__)
+#  define bpf_smp_rmb() asm volatile("dmb ishld" : : : "memory")
+#  define bpf_smp_wmb() asm volatile("dmb ishst" : : : "memory")
+# elif defined(__arm__)
+#  define bpf_smp_rmb() asm volatile("dmb ish" : : : "memory")
+#  define bpf_smp_wmb() asm volatile("dmb ishst" : : : "memory")
+# else
+#  error Architecture not supported by the XDP socket code in libbpf.
+# endif
+#endif
+
 static inline __u64 *xsk_ring_prod__fill_addr(struct xsk_ring_prod *fill,
 					      __u32 idx)
 {
@@ -119,7 +134,7 @@ static inline void xsk_ring_prod__submit(struct xsk_ring_prod *prod, size_t nb)
 	/* Make sure everything has been written to the ring before signalling
 	 * this to the kernel.
 	 */
-	smp_wmb();
+	bpf_smp_wmb();
 
 	*prod->producer += nb;
 }
@@ -133,7 +148,7 @@ static inline size_t xsk_ring_cons__peek(struct xsk_ring_cons *cons,
 		/* Make sure we do not speculatively read the data before
 		 * we have received the packet buffers from the ring.
 		 */
-		smp_rmb();
+		bpf_smp_rmb();
 
 		*idx = cons->cached_cons;
 		cons->cached_cons += entries;
-- 
2.7.4