memory barrier functions available for drivers.

git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@25183 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/os/drivers/KernelExport.h

@@ -154,6 +154,8 @@ extern status_t		unregister_kernel_daemon(daemon_hook hook, void *arg);
 
 extern void			call_all_cpus(void (*func)(void *, int), void *cookie);
 extern void			call_all_cpus_sync(void (*func)(void *, int), void *cookie);
+extern void			memory_read_barrier(void);
+extern void			memory_write_barrier(void);
 
 /* safe methods to access user memory without having to lock it */
 extern status_t		user_memcpy(void *to, const void *from, size_t size);

headers/private/kernel/arch/cpu.h

@@ -41,6 +41,10 @@ status_t arch_cpu_user_memset(void *s, char c, size_t count,
 void arch_cpu_idle(void);
 void arch_cpu_sync_icache(void *address, size_t length);
 
+void arch_cpu_memory_read_barrier(void);
+void arch_cpu_memory_write_barrier(void);
+
+
 #ifdef __cplusplus
 }
 #endif