libbb: make msleep() result in only one syscall instead of looping

function                                             old     new   delta
msleep                                                45      52      +7

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

libbb/bb_do_delay.c

@@ -36,6 +36,7 @@ void FAST_FUNC sleep1(void)
 
 void FAST_FUNC msleep(unsigned ms)
 {
+#if 0
 	/* 1. usleep(n) is not guaranteed by standards to accept n >= 1000000
 	 * 2. multiplication in usleep(ms * 1000) can overflow if ms > 4294967
 	 *    (sleep of ~71.5 minutes)
@@ -46,4 +47,21 @@ void FAST_FUNC msleep(unsigned ms)
 		ms -= 500;
 	}
 	usleep(ms * 1000);
+#else
+//usleep is often implemented as a call to nanosleep.
+//Simply do the same to implement msleep.
+//it's marginally larger, but wakes your CPU less often:
+//function    old     new   delta
+//msleep       45      52      +7
+	struct timespec ts;
+	ts.tv_sec = ms / 1000;
+	ts.tv_nsec = (ms % 1000) * 1000000;
+	/*
+	 * If a signal has non-default handler, nanosleep returns early.
+	 * Our version of msleep doesn't return early
+	 * if interrupted by such signals:
+	 */
+	while (nanosleep(&ts, &ts) != 0)
+		continue;
+#endif
 }

libbb/platform.c

@@ -27,7 +27,6 @@ int FAST_FUNC usleep(unsigned usec)
 	 * If a signal has non-default handler, nanosleep returns early.
 	 * Our version of usleep doesn't return early
 	 * if interrupted by such signals:
-	 *
 	 */
 	while (nanosleep(&ts, &ts) != 0)
 		continue;

networking/ifupdown.c

@@ -1357,15 +1357,15 @@ static FILE *open_new_state_file(void)
 					IFSTATE_FILE_PATH".new");
 		}
 		/* Someone else created the .new file */
-		if (cnt > 30 * 1000) {
+		if (cnt > 30) {
 			/* Waited for 30*30/2 = 450 milliseconds, still EEXIST.
 			 * Assuming a stale file, rewriting it.
 			 */
 			flags = (O_WRONLY | O_CREAT | O_TRUNC);
 			continue;
 		}
-		usleep(cnt);
-		cnt += 1000;
+		msleep(cnt);
+		cnt++;
 	}
 
 	return xfdopen_for_write(fd);