libkbdfile: avoid double formatting in pathname helper

kbdfile_pathname_sprintf() currently formats the same string twice to
compute size and then write output. This adds unnecessary work in a
path-building helper that is used repeatedly during file lookup.

Signed-off-by: Alexey Gladkov <legion@kernel.org>

Author: legionus

src/libkbdfile/kbdfile.c

@@ -84,23 +84,19 @@ kbdfile_set_pathname(struct kbdfile *fp, const char *pathname)
 static int KBD_ATTR_PRINTF(2, 3)
 kbdfile_pathname_sprintf(struct kbdfile *fp, const char *fmt, ...)
 {
-	ssize_t size;
+	int size;
 	va_list ap;
 
 	if (fp == NULL || fmt == NULL)
 		return -1;
 
 	va_start(ap, fmt);
-	size = vsnprintf(NULL, 0, fmt, ap);
+	size = vsnprintf(fp->pathname, sizeof(fp->pathname), fmt, ap);
 	va_end(ap);
 
 	if (size < 0 || (size_t) size >= sizeof(fp->pathname))
 		return -1;
 
-	va_start(ap, fmt);
-	vsnprintf(fp->pathname, sizeof(fp->pathname), fmt, ap);
-	va_end(ap);
-
 	return 0;
 }