mbr: Warn if MBR gap is small and user uses advanced modules

We don't want to support small MBR gap in pair with anything but the
simplest config of biosdisk + part_msdos + simple filesystem. In this
path "simple filesystems" are all current filesystems except ZFS and
Btrfs.

Signed-off-by: Vladimir Serbinenko <phcoder@google.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

include/grub/partition.h

@@ -51,11 +51,14 @@ struct grub_partition_map
   grub_err_t (*iterate) (struct grub_disk *disk,
 			 grub_partition_iterate_hook_t hook, void *hook_data);
 #ifdef GRUB_UTIL
+#define GRUB_MIN_RECOMMENDED_MBR_GAP	1900
+
   /* Determine sectors available for embedding.  */
   grub_err_t (*embed) (struct grub_disk *disk, unsigned int *nsectors,
 		       unsigned int max_nsectors,
 		       grub_embed_type_t embed_type,
-		       grub_disk_addr_t **sectors);
+		       grub_disk_addr_t **sectors,
+		       int warn_short);
 #endif
 };
 typedef struct grub_partition_map *grub_partition_map_t;