Fix usleep(3) return type to be POSIX-compliant.

POSIX usleep(3) returns 0 on successful completion, -1 otherwise:
  http://www.opengroup.org/onlinepubs/007908799/xsh/usleep.html

This was found by an external user porting native code:
  http://groups.google.com/group/android-porting/browse_thread/thread/674848f001db0292

2 files changed, 8 insertions, 5 deletions

diff --git a/libc/include/unistd.h b/libc/include/unistd.h
index 67cb5fe..954f34e 100644
--- a/libc/include/unistd.h
+++ b/libc/include/unistd.h
@@ -145,7 +145,7 @@ extern int ftruncate(int, off_t);
 extern int pause(void);
 extern unsigned int alarm(unsigned int);
 extern unsigned int sleep(unsigned int);
-extern void usleep(unsigned long);
+extern int usleep(unsigned long);
 
 extern int gethostname(char *, size_t);
 extern int sethostname(const char *, size_t);
diff --git a/libc/unistd/usleep.c b/libc/unistd/usleep.c
index 75458b1..19e8ee8 100644
--- a/libc/unistd/usleep.c
+++ b/libc/unistd/usleep.c
@@ -28,7 +28,7 @@
 #include <time.h>
 #include <errno.h>
 
-void usleep(unsigned long usec)
+int usleep(unsigned long usec)
 {
   struct timespec ts;
 
@@ -43,10 +43,13 @@ void usleep(unsigned long usec)
 
   for (;;)
   {
-    if ( nanosleep( &ts, &ts ) >= 0 )
-        break;
+    if ( nanosleep( &ts, &ts ) == 0 )
+        return 0;
 
+    // We try again if the nanosleep failure is EINTR.
+    // The other possible failures are EINVAL (which we should pass through),
+    // and ENOSYS, which doesn't happen.
     if ( errno != EINTR )
-        break;
+        return -1;
   }
 }