add 'head' field to PerlIOl struct

This allows any layer to find the top of the layer stack,
or more specifically, the entry in PL_perlio that points to
the top.

Needed for the next commit, which will implement a reference counting
scheme.

There's currently a bug in MakeMaker which causes several extensions to
miss the dependency on perliol.h having changed, so this commit includes
a gratuitous whitespace change to perl.h to hopefully force recompilation.

1 files changed, 1 insertions, 0 deletions

diff --git a/perliol.h b/perliol.h
index d3053a1067..744ffc8870 100644
--- a/perliol.h
+++ b/perliol.h
@@ -67,6 +67,7 @@ struct _PerlIO {
     PerlIOl *next;		/* Lower layer */
     PerlIO_funcs *tab;		/* Functions for this layer */
     U32 flags;			/* Various flags for state */
+    PerlIOl *head;		/* our ultimate parent pointer */
 };
 
 /*--------------------------------------------------------------------------------------*/