[XFS] Make use of the init-once slab optimisation.

To avoid having to initialise some fields of the XFS inode on every
allocation, we can use the slab init-once feature to initialise them. All
we have to guarantee is that when we free the inode, all it's entries are
in the initial state. Add asserts where possible to ensure debug kernels
check this initial state before freeing and after allocation.

SGI-PV: 981498

SGI-Modid: xfs-linux-melb:xfs-kern:31925a

Signed-off-by: David Chinner <david@fromorbit.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
index 1420c49..3af1f6d 100644
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -513,6 +513,7 @@
 				     xfs_fsize_t, int, int);
 int		xfs_iunlink(struct xfs_trans *, xfs_inode_t *);
 
+struct xfs_inode * xfs_inode_alloc(struct xfs_mount *, xfs_ino_t);
 void		xfs_idestroy_fork(xfs_inode_t *, int);
 void		xfs_idestroy(xfs_inode_t *);
 void		xfs_idata_realloc(xfs_inode_t *, int, int);