fat: move MAX_FAT to fat.h and change it to inline function

MAX_FAT is useless in msdos_fs.h, since it uses the MSDOS_SB function
that is defined in fat.h.  So really, this macro can be only called from
code that already includes fat.h.

Hence, this patch moves it to fat.h, right after MSDOS_SB is defined.  I
also changed it to an inline function in order to save the double call
to MSDOS_SB.  This was suggested by joe@perches.com in the previous
version.

This patch is required for the next in the series, in which the variant
(whether this is FAT12, FAT16 or FAT32) checks are replaced with new
macros.

Link: http://lkml.kernel.org/r/1544990640-11604-3-git-send-email-carmeli.tamir@gmail.com
Signed-off-by: Carmeli Tamir <carmeli.tamir@gmail.com>
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/fat/fat.h

@@ -142,6 +142,15 @@ static inline struct msdos_sb_info *MSDOS_SB(struct super_block *sb)
 	return sb->s_fs_info;
 }
 
+/* Maximum number of clusters */
+static inline u32 max_fat(struct super_block *sb)
+{
+	struct msdos_sb_info *sbi = MSDOS_SB(sb);
+
+	return sbi->fat_bits == 32 ? MAX_FAT32 :
+		sbi->fat_bits == 16 ? MAX_FAT16 : MAX_FAT12;
+}
+
 static inline struct msdos_inode_info *MSDOS_I(struct inode *inode)
 {
 	return container_of(inode, struct msdos_inode_info, vfs_inode);

fs/fat/inode.c

@@ -1781,7 +1781,7 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat,
 	/* check that FAT table does not overflow */
 	fat_clusters = calc_fat_clusters(sb);
 	total_clusters = min(total_clusters, fat_clusters - FAT_START_ENT);
-	if (total_clusters > MAX_FAT(sb)) {
+	if (total_clusters > max_fat(sb)) {
 		if (!silent)
 			fat_msg(sb, KERN_ERR, "count of clusters too big (%u)",
 			       total_clusters);

include/uapi/linux/msdos_fs.h

@@ -65,8 +65,6 @@
 #define MAX_FAT12	0xFF4
 #define MAX_FAT16	0xFFF4
 #define MAX_FAT32	0x0FFFFFF6
-#define MAX_FAT(s)	(MSDOS_SB(s)->fat_bits == 32 ? MAX_FAT32 : \
-	MSDOS_SB(s)->fat_bits == 16 ? MAX_FAT16 : MAX_FAT12)
 
 /* bad cluster mark */
 #define BAD_FAT12	0xFF7