Index: uspace/srv/fs/exfat/exfat_fat.c
===================================================================
--- uspace/srv/fs/exfat/exfat_fat.c	(revision 92d9406c5fcd9786b796bd3441ab6339da9c93d0)
+++ uspace/srv/fs/exfat/exfat_fat.c	(revision 177689595b433770ea9e5d3600abd913f7b901da)
@@ -50,4 +50,5 @@
 #include <malloc.h>
 #include <mem.h>
+#include <str.h>
 
 
@@ -541,5 +542,18 @@
 int exfat_sanity_check(exfat_bs_t *bs, service_id_t service_id)
 {
-	/* TODO */
+	if (str_cmp((char const *)bs->oem_name, "EXFAT   "))
+		return ENOTSUP;
+	else if (uint16_t_le2host(bs->signature) != 0xAA55)
+		return ENOTSUP;
+	else if (uint32_t_le2host(bs->fat_sector_count) == 0)
+		return ENOTSUP;
+	else if (uint32_t_le2host(bs->data_clusters) == 0)
+		return ENOTSUP;
+	else if (bs->fat_count != 1)
+		return ENOTSUP;
+	else if ((bs->bytes_per_sector + bs->sec_per_cluster) > 25) {
+		/* exFAT does not support cluster size > 32 Mb */
+		return ENOTSUP;
+	}
 	return EOK;
 }