[MEDIUM] introduce pipe pools

A new data type has been added : pipes. Some pre-allocated empty pipes
are maintained in a pool for users such as splice which use them a lot
for very short times.

Pipes are allocated using get_pipe() and released using put_pipe().
Pipes which are released with pending data are immediately killed.
The struct pipe is small (16 to 20 bytes) and may even be further
reduced by unifying ->data and ->next.

It would be nice to have a dedicated cleanup task which would watch
for the pipes usage and destroy a few of them from time to time.
diff --git a/include/types/pipe.h b/include/types/pipe.h
new file mode 100644
index 0000000..12a1eee
--- /dev/null
+++ b/include/types/pipe.h
@@ -0,0 +1,45 @@
+/*
+  include/types/pipe.h
+  Pipe management.
+
+  Copyright (C) 2000-2009 Willy Tarreau - w@1wt.eu
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation, version 2.1
+  exclusively.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+*/
+
+#ifndef _TYPES_PIPE_H
+#define _TYPES_PIPE_H
+
+#include <common/config.h>
+
+/* A pipe is described by its read and write FDs, and the data remaining in it.
+ * The FDs are valid if there are data pending. The user is not allowed to
+ * change the FDs.
+ */
+struct pipe {
+	int data;	/* number of bytes present in the pipe  */
+	int prod;	/* FD the producer must write to ; -1 if none */
+	int cons;	/* FD the consumer must read from ; -1 if none */
+	struct pipe *next;
+};
+
+#endif /* _TYPES_PIPE_H */
+
+/*
+ * Local variables:
+ *  c-indent-level: 8
+ *  c-basic-offset: 8
+ * End:
+ */