sync code with last improvements from OpenBSD

driver/xf86-video-intel/tools/backlight_helper.c

@@ -0,0 +1,58 @@
+#include <stdio.h>
+#include <string.h>
+#include <stdarg.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <errno.h>
+
+#include <sys/types.h>
+#include <sys/stat.h>
+
+#define DBG 0
+
+#if defined(__GNUC__) && (__GNUC__ > 3)
+__attribute__((format(printf, 1, 2), noreturn))
+#endif
+static void die(const char *format, ...)
+{
+	if (DBG) {
+		va_list args;
+
+		va_start(args, format);
+		vfprintf(stderr, format, args);
+		va_end(args);
+	}
+
+	exit(1);
+}
+
+int main(int argc, char *argv[])
+{
+	struct stat st;
+	char buf[1024];
+	int len, fd;
+
+	if (argc != 2)
+		die("Usage: xf86-video-intel-backlight-helper <iface>\n");
+
+	if (strchr(argv[1], '/') != NULL)
+		die("Invalid interface '%s': contains '/'\n", argv[1]);
+
+	if (snprintf(buf, sizeof(buf),
+		     "/sys/class/backlight/%s/brightness",
+		     argv[1]) >= sizeof(buf))
+		die("Invalid interface '%s': name too long\n", argv[1]);
+
+	fd = open(buf, O_RDWR);
+	if (fd < 0 || fstat(fd, &st) || major(st.st_dev))
+		die("Invalid interface '%s': unknown backlight file\n", argv[1]);
+
+	while (fgets(buf, sizeof(buf), stdin)) {
+		len = strlen(buf);
+		if (write(fd, buf, len) != len)
+			die("Failed to update backlight interface '%s': errno=%d\n", argv[1], errno);
+	}
+
+	return 0;
+}