Commit b7e3a280 authored by Magnus Karlsson's avatar Magnus Karlsson Committed by Alexei Starovoitov
Browse files

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 unnecessary 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: 1cad0788 ("libbpf: add support for using AF_XDP sockets")
Signed-off-by: default avatarMagnus Karlsson <magnus.karlsson@intel.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent a06d7296

tools/lib/bpf/libbpf_util.h

+25 −0
Original line number Diff line number Diff line
@@ -23,6 +23,31 @@ do { \ 
#define pr_info(fmt, ...)	__pr(LIBBPF_INFO, fmt, ##__VA_ARGS__)

#define pr_debug(fmt, ...)	__pr(LIBBPF_DEBUG, fmt, ##__VA_ARGS__)



/* Use these barrier functions instead of smp_[rw]mb() when they are

 * used in a libbpf header file. That way they can be built into the

 * application that uses libbpf.

 */

#if defined(__i386__) || defined(__x86_64__)

# define libbpf_smp_rmb() asm volatile("" : : : "memory")

# define libbpf_smp_wmb() asm volatile("" : : : "memory")

# define libbpf_smp_mb() \

	asm volatile("lock; addl $0,-4(%%rsp)" : : : "memory", "cc")

#elif defined(__aarch64__)

# define libbpf_smp_rmb() asm volatile("dmb ishld" : : : "memory")

# define libbpf_smp_wmb() asm volatile("dmb ishst" : : : "memory")

# define libbpf_smp_mb() asm volatile("dmb ish" : : : "memory")

#elif defined(__arm__)

/* These are only valid for armv7 and above */

# define libbpf_smp_rmb() asm volatile("dmb ish" : : : "memory")

# define libbpf_smp_wmb() asm volatile("dmb ishst" : : : "memory")

# define libbpf_smp_mb() asm volatile("dmb ish" : : : "memory")

#else

# warning Architecture missing native barrier functions in libbpf_util.h.

# define libbpf_smp_rmb() __sync_synchronize()

# define libbpf_smp_wmb() __sync_synchronize()

# define libbpf_smp_mb() __sync_synchronize()

#endif



#ifdef __cplusplus

} /* extern "C" */

#endif

tools/lib/bpf/xsk.h

+4 −3
Original line number Diff line number Diff line
@@ -16,6 +16,7 @@ 
#include <linux/if_xdp.h>



#include "libbpf.h"

#include "libbpf_util.h"



#ifdef __cplusplus

extern "C" {
@@ -123,7 +124,7 @@ 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 indicating

	 * this to the kernel by writing the producer pointer.

	 */

	smp_wmb();

	libbpf_smp_wmb();



	*prod->producer += nb;

}
@@ -137,7 +138,7 @@ 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();

		libbpf_smp_rmb();



		*idx = cons->cached_cons;

		cons->cached_cons += entries;
@@ -151,7 +152,7 @@ static inline void xsk_ring_cons__release(struct xsk_ring_cons *cons, size_t nb) 
	/* Make sure data has been read before indicating we are done

	 * with the entries by updating the consumer pointer.

	 */

	smp_mb();

	libbpf_smp_mb();



	*cons->consumer += nb;

}

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