+# Check if passed file is a valid one for NAND sysupgrade. Currently it accepts
+# 3 types of files:
+# 1) UBI - should contain an ubinized image, header is checked for the proper
+# MAGIC
+# 2) UBIFS - should contain UBIFS partition that will replace "rootfs" volume,
+# header is checked for the proper MAGIC
+# 3) TRX - archive has to include "sysupgrade-BOARD" directory with a non-empty
+# "CONTROL" file (at this point its content isn't verified)
+#
+# You usually want to call this function in platform_check_image.
+#
+# $(1): board name, used in case of passing TRX file
+# $(2): file to be checked