libbpf: xsk: Remove linux/compiler.h header

In commit 291471dd1559 ("libbpf, xsk: Add libbpf_smp_store_release
libbpf_smp_load_acquire") linux/compiler.h was added as a dependency
to xsk.h, which is the user-facing API. This makes it harder for
userspace application to consume the library. Here the header
inclusion is removed, and instead {READ,WRITE}_ONCE() is added
explicitly.

Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210310080929.641212-2-bjorn.topel@gmail.com

diff --git a/tools/lib/bpf/libbpf_util.h b/tools/lib/bpf/libbpf_util.h
index cfbcfc063c81c96c558e9626b030d23dcc32601e..954da9b34a3481595b41eb8bc18e11b221794316 100644 (file)
--- a/tools/lib/bpf/libbpf_util.h
+++ b/tools/lib/bpf/libbpf_util.h
@@ -5,25 +5,30 @@
 #define __LIBBPF_LIBBPF_UTIL_H
 
 #include <stdbool.h>
-#include <linux/compiler.h>
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-/* 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.
+/* Load-Acquire Store-Release barriers used by the XDP socket
+ * library. The following macros should *NOT* be considered part of
+ * the xsk.h API, and is subject to change anytime.
+ *
+ * LIBRARY INTERNAL
  */
+
+#define __XSK_READ_ONCE(x) (*(volatile typeof(x) *)&x)
+#define __XSK_WRITE_ONCE(x, v) (*(volatile typeof(x) *)&x) = (v)
+
 #if defined(__i386__) || defined(__x86_64__)
 # define libbpf_smp_store_release(p, v)                                        \
        do {                                                            \
                asm volatile("" : : : "memory");                        \
-               WRITE_ONCE(*p, v);                                      \
+               __XSK_WRITE_ONCE(*p, v);                                \
        } while (0)
 # define libbpf_smp_load_acquire(p)                                    \
        ({                                                              \
-               typeof(*p) ___p1 = READ_ONCE(*p);                       \
+               typeof(*p) ___p1 = __XSK_READ_ONCE(*p);                 \
                asm volatile("" : : : "memory");                        \
                ___p1;                                                  \
        })
@@ -41,11 +46,11 @@ extern "C" {
 # define libbpf_smp_store_release(p, v)                                        \
        do {                                                            \
                asm volatile ("fence rw,w" : : : "memory");             \
-               WRITE_ONCE(*p, v);                                      \
+               __XSK_WRITE_ONCE(*p, v);                                \
        } while (0)
 # define libbpf_smp_load_acquire(p)                                    \
        ({                                                              \
-               typeof(*p) ___p1 = READ_ONCE(*p);                       \
+               typeof(*p) ___p1 = __XSK_READ_ONCE(*p);                 \
                asm volatile ("fence r,rw" : : : "memory");             \
                ___p1;                                                  \
        })
@@ -55,19 +60,21 @@ extern "C" {
 #define libbpf_smp_store_release(p, v)                                 \
        do {                                                            \
                __sync_synchronize();                                   \
-               WRITE_ONCE(*p, v);                                      \
+               __XSK_WRITE_ONCE(*p, v);                                \
        } while (0)
 #endif
 
 #ifndef libbpf_smp_load_acquire
 #define libbpf_smp_load_acquire(p)                                     \
        ({                                                              \
-               typeof(*p) ___p1 = READ_ONCE(*p);                       \
+               typeof(*p) ___p1 = __XSK_READ_ONCE(*p);                 \
                __sync_synchronize();                                   \
                ___p1;                                                  \
        })
 #endif
 
+/* LIBRARY INTERNAL -- END */
+
 #ifdef __cplusplus
 } /* extern "C" */
 #endif