First working filters implementaton.

Only downstream filters are supported currently, i.e. no result
set filtering can be done.

A crude QLA (Query Log All) filter is included as a test harness only

server/include/filter.h

@@ -0,0 +1,96 @@
+#ifndef _FILTER_H
+#define _FILTER_H
+/*
+ * This file is distributed as part of the SkySQL Gateway.  It is free
+ * software: you can redistribute it and/or modify it under the terms of the
+ * GNU General Public License as published by the Free Software Foundation,
+ * version 2.
+ *
+ * This program 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 General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc., 51
+ * Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Copyright SkySQL Ab 2014
+ */
+
+/**
+ * @file filter.h -  The filter interface mechanisms
+ *
+ * Revision History
+ *
+ * Date		Who			Description
+ * 27/05/2014	Mark Riddoch		Initial implementation
+ *
+ */
+#include <dcb.h>
+#include <session.h>
+#include <buffer.h>
+#include <stdint.h>
+
+/**
+ * The FILTER handle points to module specific data, so the best we can do
+ * is to make it a void * externally.
+ */
+typedef void *FILTER;
+/**
+ * @verbatim
+ * The "module object" structure for a query router module
+ *
+ * The entry points are:
+ * 	createInstance		Called by the service to create a new
+ * 				instance of the filter 
+ * 	newSession		Called to create a new user session
+ * 				within the filter
+ * 	closeSession		Called when a session is closed
+ * 	freeSession		Called when a session is freed
+ *	setDownstream		Sets the downstream component of the
+ *				filter pipline
+ * 	routeQuery		Called on each query that requires
+ * 				routing
+ * 	diagnostics		Called to force the filter to print
+ * 				diagnostic output
+ *
+ * @endverbatim
+ *
+ * @see load_module
+ */
+typedef struct filter_object {
+	FILTER	*(*createInstance)(char **options);
+	void	*(*newSession)(FILTER *instance, SESSION *session);
+	void 	(*closeSession)(FILTER *instance, void *fsession);
+        void 	(*freeSession)(FILTER *instance, void *fsession);
+	void	(*setDownstream)(FILTER *instance, void *fsession, DOWNSTREAM *downstream);
+	int	(*routeQuery)(FILTER *instance, void *fsession, GWBUF *queue);
+	void	(*diagnostics)(FILTER *instance, void *fsession, DCB *dcb);
+} FILTER_OBJECT;
+
+/**
+ * The definition of a filter form the configuration file.
+ * This is basically the link between a plugin to load and the
+ * optons to pass to that plugin.
+ */
+typedef struct filter_def {
+	char		*name;		/*< The Filter name */
+	char		*module;	/*< The module to load */
+	char		**options;	/*< The options set for this filter */
+	FILTER		filter;
+	FILTER_OBJECT	*obj;
+	SPINLOCK	spin;
+	struct	filter_def
+			*next;		/*< Next filter in the chain of all filters */
+} FILTER_DEF;
+
+FILTER_DEF	*filter_alloc(char *, char *);
+void		filter_free(FILTER_DEF *);
+FILTER_DEF	*filter_find(char *);
+void		filterAddOption(FILTER_DEF *, char *);
+DOWNSTREAM	*filterApply(FILTER_DEF *, SESSION *, DOWNSTREAM *);
+void		dprintAllFilters(DCB *);
+void		dprintFilter(DCB *, FILTER_DEF *);
+void		dListFilters(DCB *);
+#endif