dcache: Add case-insensitive support d_ci_add() routine

This add a dcache entry to the dcache for lookup, but changing the name
that is associated with the entry rather than the one passed in to the
lookup routine.

First, it sees if the case-exact match already exists in the dcache and
uses it if one exists. Otherwise, it allocates a new node with the new
name and splices it into the dcache.

Original code from ntfs_lookup in fs/ntfs/namei.c by Anton Altaparmakov.

Signed-off-by: Barry Naujok <bnaujok@sgi.com>
Signed-off-by: Anton Altaparmakov <aia21@cantab.net>
Acked-by: Christoph Hellwig <hch@infradead.org>
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 98202c6..07aa198 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -230,6 +230,7 @@
 extern struct dentry * d_alloc(struct dentry *, const struct qstr *);
 extern struct dentry * d_alloc_anon(struct inode *);
 extern struct dentry * d_splice_alias(struct inode *, struct dentry *);
+extern struct dentry * d_add_ci(struct inode *, struct dentry *, struct qstr *);
 extern void shrink_dcache_sb(struct super_block *);
 extern void shrink_dcache_parent(struct dentry *);
 extern void shrink_dcache_for_umount(struct super_block *);