[XFS] keep i_nlink updated and use proper accessors

To get the read-only bind mounts in -mm to work correctly with XFS we need
to call the drop_nlink and inc_nlink helpers to monitor the link count.
Add calls to these to xfs_bumplink and xfs_droplink and stop copying over
di_nlink to i_nlink in xfs_validate_fields and vn_revalidate.

SGI-PV: 971186
SGI-Modid: xfs-linux-melb:xfs-kern:30392a

Signed-off-by: Christoph Hellwig <[e-mail]>
Signed-off-by: Lachlan McIlroy <[e-mail]>

fs/xfs/linux-2.6/xfs_iops.c

···
 	struct xfs_inode	*ip = XFS_I(inode);
 	loff_t size;
 
-	inode->i_nlink = ip->i_d.di_nlink;
 	/* we're under i_sem so i_size can't change under us */
 	size = XFS_ISIZE(ip);
 	if (i_size_read(inode) != size)

fs/xfs/linux-2.6/xfs_vnode.c

···
 
 	xfs_ilock(ip, XFS_ILOCK_SHARED);
 	inode->i_mode	    = ip->i_d.di_mode;
-	inode->i_nlink	    = ip->i_d.di_nlink;
 	inode->i_uid	    = ip->i_d.di_uid;
 	inode->i_gid	    = ip->i_d.di_gid;
 	inode->i_mtime.tv_sec = ip->i_d.di_mtime.t_sec;

fs/xfs/xfs_utils.c

···
 
 	ASSERT (ip->i_d.di_nlink > 0);
 	ip->i_d.di_nlink--;
+	drop_nlink(ip->i_vnode);
 	xfs_trans_log_inode(tp, ip, XFS_ILOG_CORE);
 
 	error = 0;
···
 
 	ASSERT(ip->i_d.di_nlink > 0);
 	ip->i_d.di_nlink++;
+	inc_nlink(ip->i_vnode);
 	if ((ip->i_d.di_version == XFS_DINODE_VERSION_1) &&
 	    (ip->i_d.di_nlink > XFS_MAXLINK_1)) {
 		/*