cmd: Add the 'btrsubvol' command to list BTRFS subvolumes

Signed-off-by: Marek Behun <marek.behun@nic.cz>

 create mode 100644 cmd/btrfs.c
diff --git a/cmd/btrfs.c b/cmd/btrfs.c
new file mode 100644
index 0000000..3f4f1b7
--- /dev/null
+++ b/cmd/btrfs.c
@@ -0,0 +1,28 @@
+/*
+ * 2017 by Marek Behun <marek.behun@nic.cz>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <common.h>
+#include <command.h>
+#include <btrfs.h>
+#include <fs.h>
+
+int do_btrsubvol(cmd_tbl_t *cmdtp, int flag, int argc, char *const argv[])
+{
+	if (argc != 3)
+		return CMD_RET_USAGE;
+
+	if (fs_set_blk_dev(argv[1], argv[2], FS_TYPE_BTRFS))
+		return 1;
+
+	btrfs_list_subvols();
+	return 0;
+}
+
+U_BOOT_CMD(btrsubvol, 3, 1, do_btrsubvol,
+	"list subvolumes of a BTRFS filesystem",
+	"<interface> <dev[:part]>\n"
+	"     - List subvolumes of a BTRFS filesystem."
+)