libbacklight: Fix backlight never gets initialized

In 913d7c15f7 stricter error checking was
introduced to the strtol call, which broke reading backlight values.
Since every sysfs backlight file ends with a newline.

As noted in a comment in the previous MR to prevent damaged pointers
after calling asprintf, replace every asprintf call with str_printf.

Previous-MR: https://gitlab.freedesktop.org/wayland/weston/-/merge_requests/543

Signed-off-by: Sören Meier <soerenmeier@livgood.ch>

libweston/backend-drm/libbacklight.c

@@ -53,8 +53,10 @@ static long backlight_get(struct backlight *backlight, char *node)
 	int fd, value;
 	long ret;
 
-	if (asprintf(&path, "%s/%s", backlight->path, node) < 0)
+	str_printf(&path, "%s/%s", backlight->path, node);
+	if (!path)
 		return -ENOMEM;
+
 	fd = open(path, O_RDONLY);
 	if (fd < 0) {
 		ret = -1;
@@ -67,6 +69,9 @@ static long backlight_get(struct backlight *backlight, char *node)
 		goto out;
 	}
 
+	if (buffer[ret - 1] == '\n')
+		buffer[ret - 1] = '\0';
+
 	if (!safe_strtoint(buffer, &value)) {
 		ret = -1;
 		goto out;
@@ -103,7 +108,8 @@ long backlight_set_brightness(struct backlight *backlight, long brightness)
 	int fd;
 	long ret;
 
-	if (asprintf(&path, "%s/%s", backlight->path, "brightness") < 0)
+	str_printf(&path, "%s/%s", backlight->path, "brightness");
+	if (!path)
 		return -ENOMEM;
 
 	fd = open(path, O_RDWR);
@@ -118,7 +124,8 @@ long backlight_set_brightness(struct backlight *backlight, long brightness)
 		goto out;
 	}
 
-	if (asprintf(&buffer, "%ld", brightness) < 0) {
+	str_printf(&buffer, "%ld", brightness);
+	if (!buffer) {
 		ret = -1;
 		goto out;
 	}
@@ -171,7 +178,8 @@ struct backlight *backlight_init(struct udev_device *drm_device,
 	if (!syspath)
 		return NULL;
 
-	if (asprintf(&path, "%s/%s", syspath, "device") < 0)
+	str_printf(&path, "%s/%s", syspath, "device");
+	if (!path)
 		return NULL;
 
 	ret = readlink(path, buffer, sizeof(buffer) - 1);
@@ -214,11 +222,13 @@ struct backlight *backlight_init(struct udev_device *drm_device,
 		if (entry->d_name[0] == '.')
 			continue;
 
-		if (asprintf(&backlight_path, "%s/%s", "/sys/class/backlight",
-			     entry->d_name) < 0)
+		str_printf(&backlight_path, "%s/%s", "/sys/class/backlight",
+			   entry->d_name);
+		if (!backlight_path)
 			goto err;
 
-		if (asprintf(&path, "%s/%s", backlight_path, "type") < 0) {
+		str_printf(&path, "%s/%s", backlight_path, "type");
+		if (!path) {
 			free(backlight_path);
 			goto err;
 		}
@@ -255,7 +265,8 @@ struct backlight *backlight_init(struct udev_device *drm_device,
 
 		free (path);
 
-		if (asprintf(&path, "%s/%s", backlight_path, "device") < 0)
+		str_printf(&path, "%s/%s", backlight_path, "device");
+		if (!path)
 			goto err;
 
 		ret = readlink(path, buffer, sizeof(buffer) - 1);