Man page 9 : d_splice_alias

d_splice_alias - splice a disconnected dentry into the tree if one exists

struct dentry * d_splice_alias(struct inode *  inode , struct dentry *  dentry );

inode
    the inode which may have a disconnected dentry

dentry
    a negative dentry which we want to point to the inode.

If inode is a directory and has a AqdisconnectedAq dentry (i.e. IS_ROOT and DCACHE_DISCONNECTED), then d_move that in place of the given dentry and return it, else simply d_add the inode to the dentry and return NULL.

This is needed in the lookup routine of any filesystem that is exportable (via knfsd) so that we can build dcache paths to directories effectively.

If a dentry was found and moved, then it is returned. Otherwise NULL is returned. This matches the expected return value of ->lookup.