fat: add extended fileds to struct fat_boot_sector

Later we will need "state" field to check if volume was cleanly unmounted.
Signed-off-by: Oleksij Rempel <bug-track@fisher-privat.net>
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/fat/inode.c

@@ -1298,17 +1298,17 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat,
 	sbi->prev_free = FAT_START_ENT;
 	sb->s_maxbytes = 0xffffffff;
 
-	if (!sbi->fat_length && b->fat32_length) {
+	if (!sbi->fat_length && b->fat32.length) {
 		struct fat_boot_fsinfo *fsinfo;
 		struct buffer_head *fsinfo_bh;
 
 		/* Must be FAT32 */
 		sbi->fat_bits = 32;
-		sbi->fat_length = le32_to_cpu(b->fat32_length);
-		sbi->root_cluster = le32_to_cpu(b->root_cluster);
+		sbi->fat_length = le32_to_cpu(b->fat32.length);
+		sbi->root_cluster = le32_to_cpu(b->fat32.root_cluster);
 
 		/* MC - if info_sector is 0, don't multiply by 0 */
-		sbi->fsinfo_sector = le16_to_cpu(b->info_sector);
+		sbi->fsinfo_sector = le16_to_cpu(b->fat32.info_sector);
 		if (sbi->fsinfo_sector == 0)
 			sbi->fsinfo_sector = 1;
 

include/uapi/linux/msdos_fs.h

@@ -120,14 +120,34 @@ struct fat_boot_sector {
 	__le32	hidden;		/* hidden sectors (unused) */
 	__le32	total_sect;	/* number of sectors (if sectors == 0) */
 
-	/* The following fields are only used by FAT32 */
-	__le32	fat32_length;	/* sectors/FAT */
-	__le16	flags;		/* bit 8: fat mirroring, low 4: active fat */
-	__u8	version[2];	/* major, minor filesystem version */
-	__le32	root_cluster;	/* first cluster in root directory */
+	union {
+		struct {
+			/*  Extended BPB Fields for FAT16 */
+			__u8	drive_number;	/* Physical drive number */
+			__u8	state;		/* undocumented, but used
+						   for mount state. */
+			/* other fiealds are not added here */
+		} fat16;
+
+		struct {
+			/* only used by FAT32 */
+			__le32	length;		/* sectors/FAT */
+			__le16	flags;		/* bit 8: fat mirroring,
+						   low 4: active fat */
+			__u8	version[2];	/* major, minor filesystem
+						   version */
+			__le32	root_cluster;	/* first cluster in
+						   root directory */
 			__le16	info_sector;	/* filesystem info sector */
 			__le16	backup_boot;	/* backup boot sector */
 			__le16	reserved2[6];	/* Unused */
+			/* Extended BPB Fields for FAT32 */
+			__u8	drive_number;   /* Physical drive number */
+			__u8    state;       	/* undocumented, but used
+						   for mount state. */
+			/* other fiealds are not added here */
+		} fat32;
+	};
 };
 
 struct fat_boot_fsinfo {