[PATCH] fat: Fix non-atomic NFS i_pos read

["Steven J. Magnani" <steve@digidescorp.com>]

fat_encode_fh() can fetch an invalid i_pos value on systems
where 64-bit accesses are not atomic. Make it use the same
accessor as the rest of the FAT code.

Signed-off-by: Steven J. Magnani <steve@digidescorp.com>
---
diff -uprN linux-3.5-rc4/fs/fat/inode.c new/fs/fat/inode.c
--- linux-3.5-rc4/fs/fat/inode.c	2012-06-29 11:20:12.781348652 -0500
+++ new/fs/fat/inode.c	2012-06-29 11:25:29.484713183 -0500
@@ -738,22 +738,22 @@ static int
 fat_encode_fh(struct inode *inode, __u32 *fh, int *lenp, struct inode *parent)
 {
 	int len = *lenp;
-	u32 ipos_h, ipos_m, ipos_l;
+	struct super_block *sb = inode->i_sb;
+	struct msdos_sb_info *sbi = MSDOS_SB(sb);
+	loff_t i_pos;
 
 	if (len < 5) {
 		*lenp = 5;
 		return 255; /* no room */
 	}
 
-	ipos_h = MSDOS_I(inode)->i_pos >> 8;
-	ipos_m = (MSDOS_I(inode)->i_pos & 0xf0) << 24;
-	ipos_l = (MSDOS_I(inode)->i_pos & 0x0f) << 28;
+	i_pos = fat_i_pos_read(sbi, inode);
 	*lenp = 5;
 	fh[0] = inode->i_ino;
 	fh[1] = inode->i_generation;
-	fh[2] = ipos_h;
-	fh[3] = ipos_m | MSDOS_I(inode)->i_logstart;
-	fh[4] = ipos_l;
+	fh[2] = i_pos >> 8;
+	fh[3] = ((i_pos & 0xf0) << 24) | MSDOS_I(inode)->i_logstart;
+	fh[4] = (i_pos & 0x0f) << 28;
 	if (parent)
 		fh[4] |= MSDOS_I(parent)->i_logstart;
 	return 3;