udev: modernize udev-builtin-btrfs a bit

Let's in particular log an even if a device name is too long for the
btrfs ioctl structure, instead of truncating it (which could
theoretically reference a different device).

src/udev/udev-builtin-btrfs.c

@@ -14,14 +14,12 @@
 
 static int builtin_btrfs(UdevEvent *event, int argc, char *argv[]) {
         sd_device *dev = ASSERT_PTR(ASSERT_PTR(event)->dev);
-        struct btrfs_ioctl_vol_args args = {};
-        _cleanup_close_ int fd = -EBADF;
         int r;
 
         if (argc != 3 || !streq(argv[1], "ready"))
                 return log_device_error_errno(dev, SYNTHETIC_ERRNO(EINVAL), "Invalid arguments");
 
-        fd = open("/dev/btrfs-control", O_RDWR|O_CLOEXEC|O_NOCTTY);
+        _cleanup_close_ int fd = open("/dev/btrfs-control", O_RDWR|O_CLOEXEC|O_NOCTTY);
         if (fd < 0) {
                 if (ERRNO_IS_DEVICE_ABSENT(errno)) {
                         /* Driver not installed? Then we aren't ready. This is useful in initrds that lack
@@ -34,7 +32,11 @@ static int builtin_btrfs(UdevEvent *event, int argc, char *argv[]) {
                 return log_device_debug_errno(dev, errno, "Failed to open /dev/btrfs-control: %m");
         }
 
-        strscpy(args.name, sizeof(args.name), argv[2]);
+        struct btrfs_ioctl_vol_args args = {};
+        if (strlen(argv[2]) >= sizeof(args.name))
+                return log_device_debug_errno(dev, SYNTHETIC_ERRNO(EINVAL), "Device name too long for BTRFS_IOC_DEVICES_READY call: %s", argv[2]);
+
+        strncpy(args.name, argv[2], sizeof(args.name));
         r = ioctl(fd, BTRFS_IOC_DEVICES_READY, &args);
         if (r < 0)
                 return log_device_debug_errno(dev, errno, "Failed to call BTRFS_IOC_DEVICES_READY: %m");