add atomic refcnt and locks.

It might be unnecessary, if open/close can be done without lock.

src/atomic.h

@@ -0,0 +1,58 @@
+#ifndef _ATOMIC_H_
+#define _ATOMIC_H_
+
+#include <stdlib.h>
+#include <pthread.h>
+#include <util.h>
+
+typedef int refcnt;
+
+static inline void refcnt_inc(refcnt *cnt)
+{
+        __sync_add_and_fetch(cnt, 1);
+}
+
+static inline void refcnt_dec(refcnt *cnt)
+{
+        __sync_sub_and_fetch(cnt, 1);
+}
+
+
+typedef pthread_mutex_t lock;
+
+static inline void lock_init(lock *l)
+{
+        pthread_mutex_init(l, NULL);
+}
+
+static inline void lock_acquire(lock *l)
+{
+        int ret = pthread_mutex_lock(l);
+        if (ret < 0) {
+                switch (ret) {
+                case EINVAL:
+                        pr_err("invalid mutex\n");
+                        exit(1);
+                case EDEADLK:
+                        pr_err("a deadlock would occur\n");
+                        exit(1);
+                }
+        }
+}
+
+static inline void lock_release(lock *l)
+{
+        int ret = pthread_mutex_unlock(l);
+        if (ret < 0) {
+                switch (ret) {
+                case EINVAL:
+                        pr_err("invalid mutex\n");
+                        exit(1);
+                case EPERM:
+                        pr_err("this thread does not hold this mutex\n");
+                        exit(1);
+                }
+        }
+}
+
+#endif /* _ATOMIC_H_ */