xfs: fix up inode32/64 (re)mount handling

inode32/inode64 allocator behavior with respect to mount, remount
and growfs is a little tricky.

The inode32 mount option should only enable the inode32 allocator
heuristics if the filesystem is large enough for 64-bit inodes to
exist.  Today, it has this behavior on the initial mount, but a
remount with inode32 unconditionally changes the allocation
heuristics, even for a small fs.

Also, an inode32 mounted small filesystem should transition to the
inode32 allocator if the filesystem is subsequently grown to a
sufficient size.  Today that does not happen.

This patch consolidates xfs_set_inode32 and xfs_set_inode64 into a
single new function, and moves the "is the maximum inode number big
enough to matter" test into that function, so it doesn't rely on the
caller to get it right - which remount did not do, previously.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

diff --git a/fs/xfs/xfs_super.h b/fs/xfs/xfs_super.h
index 499058f..2dfb1ce 100644
--- a/fs/xfs/xfs_super.h
+++ b/fs/xfs/xfs_super.h
@@ -65,8 +65,8 @@
 
 extern void xfs_flush_inodes(struct xfs_mount *mp);
 extern void xfs_blkdev_issue_flush(struct xfs_buftarg *);
-extern xfs_agnumber_t xfs_set_inode32(struct xfs_mount *, xfs_agnumber_t agcount);
-extern xfs_agnumber_t xfs_set_inode64(struct xfs_mount *, xfs_agnumber_t agcount);
+extern xfs_agnumber_t xfs_set_inode_alloc(struct xfs_mount *,
+					   xfs_agnumber_t agcount);
 
 extern const struct export_operations xfs_export_operations;
 extern const struct xattr_handler *xfs_xattr_handlers[];