util: Optimize path_encode

strncpy() shows up in profiling.
Since we already know the length, use memcpy() instead.

Measured 2% _user_ cpu time reduction on EeePC coldplug

index 0ff121d..6586d1c 100644
@@ -114,7 +114,6 @@ size_t util_path_encode(char *s, size_t len)
 	char t[(len * 3)+1];
 	size_t i, j;
 
-	t[0] = '\0';
 	for (i = 0, j = 0; s[i] != '\0'; i++) {
 		if (s[i] = '/') {
 			memcpy(&t[j], "\\x2f", 4);

@@ -127,8 +126,11 @@ size_t util_path_encode(char *s, size_t len)
 			j++;
 		}
 	}
-	t[j] = '\0';
-	strncpy(s, t, len);
+	if (len = 0)
+		return j;
+	i = (j < len - 1) ? j : len - 1;
+	memcpy(s, t, i);
+	s[i] = '\0';
 	return j;
 }
 

Applied.

Thanks,
Kay

Ah... just realised it wasn't the normal C string length inefficiency. The problem was strncpy() doesn't stop after writing the terminating NUL; by definition it goes on to zero the entire buffer.

I spy another use of strncpy in udev_device_add_property_from_string(), which is responsible for another ~1% user cpu time...

BTW I'm still polishing threaded udevd in my spare time. It has 4 TODOs; I will post it soon anyway, but I need to write a few explanatory words first. I have coarse-grained patch descriptions, but there are a couple of obvious questions I would like to pre-answer :).