[patch 5/6] statistics infrastructure

[Martin Peschke]

... posting was too big and bounced, next try

[patch 5/6] statistics infrastructure

This patch adds statistics infrastructure as common code.

In accordance to pending changes for other archs I introduced an
"Instrumentation Support" menu, where I added an entry for the statistics
infrastructure. I didn't bother to add this entry for other architectures.
Please do so if you are interested in exploiting statistics on non-s390
architectures.

Signed-off-by: Martin Peschke <mp3@xxxxxxxxxx>
---

 MAINTAINERS                |    7
 arch/s390/Kconfig          |    6
 arch/s390/oprofile/Kconfig |    5
 include/linux/statistic.h  |  449 +++++++++
 lib/Kconfig.statistic      |   12
 lib/Makefile               |    1
 lib/statistic.c            | 2183 +++++++++++++++++++++++++++++++++++++++++++++
 7 files changed, 2658 insertions(+), 5 deletions(-)

diff -Nurp e/arch/s390/Kconfig f/arch/s390/Kconfig
--- e/arch/s390/Kconfig	2005-10-28 02:02:08.000000000 +0200
+++ f/arch/s390/Kconfig	2005-12-14 14:22:54.000000000 +0100
@@ -481,8 +481,14 @@ source "drivers/net/Kconfig"

 source "fs/Kconfig"

+menu "Instrumentation Support"
+
 source "arch/s390/oprofile/Kconfig"

+source "lib/Kconfig.statistic"
+
+endmenu
+
 source "arch/s390/Kconfig.debug"

 source "security/Kconfig"
diff -Nurp e/arch/s390/oprofile/Kconfig f/arch/s390/oprofile/Kconfig
--- e/arch/s390/oprofile/Kconfig	2005-10-28 02:02:08.000000000 +0200
+++ f/arch/s390/oprofile/Kconfig	2005-12-14 14:22:54.000000000 +0100
@@ -1,6 +1,3 @@
-
-menu "Profiling support"
-
 config PROFILING
 	bool "Profiling support"
 	help
@@ -18,5 +15,3 @@ config OPROFILE

 	  If unsure, say N.

-endmenu
-
diff -Nurp e/include/linux/statistic.h f/include/linux/statistic.h
--- e/include/linux/statistic.h	1970-01-01 01:00:00.000000000 +0100
+++ f/include/linux/statistic.h	2005-12-14 14:22:54.000000000 +0100
@@ -0,0 +1,449 @@
+/*
+ * include/linux/statistic.h
+ *
+ * Statistics facility
+ *
+ * (C) Copyright IBM Corp. 2005
+ *
+ * Author(s): Martin Peschke <mp3@xxxxxxxxxx>
+ *
+ * This program 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; either version 2, or (at your option)
+ * any later version.
+ *
+ * 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., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#ifndef STATISTIC_H
+#define STATISTIC_H
+
+#define STATISTIC_H_REVISION "$Revision: 1.5 $"
+
+#include <linux/fs.h>
+#include <linux/types.h>
+#include <linux/spinlock.h>
+#include <linux/sgrb.h>
+
+#define STATISTIC_ROOT_DIR	"statistics"
+
+#define STATISTIC_FILENAME_DATA	"data"
+#define STATISTIC_FILENAME_DEF	"definition"
+
+#define STATISTIC_NAME_SIZE	64
+
+#define STATISTIC_RANGE_MIN	-0x7fffffffffffffffLL
+#define STATISTIC_RANGE_MAX	 0x7ffffffffffffffeLL
+
+enum {
+	STATISTIC_DEF_NAME,
+	STATISTIC_DEF_UNIT,
+	STATISTIC_DEF_TYPE_VALUE,
+	STATISTIC_DEF_TYPE_RANGE,
+	STATISTIC_DEF_TYPE_ARRAY,
+	STATISTIC_DEF_TYPE_LIST,
+	STATISTIC_DEF_TYPE_RAW,
+	STATISTIC_DEF_TYPE_HISTORY,
+	STATISTIC_DEF_ON,
+	STATISTIC_DEF_OFF,
+	STATISTIC_DEF_STARTED,
+	STATISTIC_DEF_STOPPED,
+	STATISTIC_DEF_RANGEMIN,
+	STATISTIC_DEF_RANGEMAX,
+	STATISTIC_DEF_SCALE_LIN,
+	STATISTIC_DEF_SCALE_LOG2,
+	STATISTIC_DEF_ENTRIESMAX,
+	STATISTIC_DEF_BASEINT,
+	STATISTIC_DEF_HITSMISSED,
+	STATISTIC_DEF_HITSOUT,
+	STATISTIC_DEF_RESET,
+	STATISTIC_DEF_MODE_INC,
+	STATISTIC_DEF_MODE_PROD,
+	STATISTIC_DEF_MODE_RANGE,
+	STATISTIC_DEF_PERIOD,
+	STATISTIC_DEF_VOID,
+};
+
+struct statistic;
+struct statistic_file_private;
+
+typedef void (statistic_release_fn) (struct statistic *);
+typedef void (statistic_reset_fn) (struct statistic *);
+typedef int (statistic_format_data_fn)
+		(struct statistic *, struct statistic_file_private *);
+typedef int (statistic_format_def_fn) (struct statistic *, char *);
+typedef u64 (statistic_add_fn) (struct statistic *, s64, u64);
+
+struct statistic_entry_list {
+	struct list_head	list;
+	s64			value;
+	u64			hits;
+};
+
+struct statistic_entry_raw {
+	u64 clock;
+	u64 serial;
+	s64 value;
+	u64 incr;
+};
+
+struct statistic_entry_range {
+	u32 res;
+	u32 num;	/* FIXME: better 64 bit; do_div can't deal with it) */
+	s64 acc;
+	s64 min;
+	s64 max;
+};
+
+struct statistic {
+	struct list_head		list;
+	struct statistic_interface	*interface;
+	struct statistic		**stat_ptr;
+	statistic_release_fn		*release;
+	statistic_reset_fn		*reset;
+	statistic_format_data_fn	*format_data;
+	statistic_format_def_fn		*format_def;
+	statistic_add_fn		*add;
+	char	name[STATISTIC_NAME_SIZE];
+	char	units[STATISTIC_NAME_SIZE];
+	u8	type;
+	u8	on;
+	u64	started;
+	u64	stopped;
+	u64	age;
+	s64 	range_min;
+	s64 	range_max;
+	u64	hits_out_of_range;
+	union {
+		struct {
+			/* data */
+			u64 hits;
+			/* user-writeable */
+			int mode;
+		} value;
+		struct {
+			/* data */
+			struct statistic_entry_range range;
+		} range;
+		struct {
+			/* data */
+			u64 *hits;
+			/* user-writeable */
+			u32 base_interval;
+			u8 scale;
+			/* internal */
+			u32 entries;
+		} array;
+		struct {
+			/* data */
+			struct list_head entry_lh;
+			/* user-writeable */
+			u32 entries_max;
+			/* informational for user */
+			u64 hits_missed;
+			/* internal */
+			u32 entries;
+		} list;
+		struct {
+			/* data */
+			struct sgrb rb;
+			/* user-writeable */
+			u32 entries_max;
+			/* internal */
+			u64 next_serial;
+		} raw;
+		struct {
+			/* data */
+			struct sgrb rb;
+			/* user-writeable */
+			u32 entries_max;
+			int mode;
+			u64 period;
+			/* internal */
+			u64 checkpoint;
+			u64 window;
+			u8 entry_size;
+		} history;
+	} data;
+};
+
+struct statistic_interface {
+	struct list_head	list;
+	struct dentry		*debugfs_dir;
+	struct dentry		*data_file;
+	struct dentry		*def_file;
+	struct list_head	statistic_lh;
+	struct semaphore	sem;
+	spinlock_t		lock;
+};
+
+struct statistic_file_private {
+	struct list_head read_seg_lh;
+	struct list_head write_seg_lh;
+	size_t write_seg_total_size;
+};
+
+struct statistic_global_data {
+	struct dentry		*root_dir;
+	struct list_head	interface_lh;
+	struct semaphore	sem;
+};
+
+#ifdef CONFIG_STATISTICS
+
+#define statistic_lock(interface, flags)	\
+		spin_lock_irqsave(&(interface)->lock, flags)
+#define statistic_unlock(interface, flags)	\
+		spin_unlock_irqrestore(&(interface)->lock, flags)
+
+extern int statistic_interface_create(struct statistic_interface **,
+				      const char *);
+extern int statistic_interface_remove(struct statistic_interface **);
+
+extern int statistic_create(struct statistic **, struct statistic_interface *,
+			    const char *, const char *);
+extern int statistic_remove(struct statistic **);
+
+extern int statistic_define_value(struct statistic *, s64, s64, int);
+extern int statistic_define_range(struct statistic *, s64, s64);
+extern int statistic_define_array(struct statistic *, s64, s64, u32, u8);
+extern int statistic_define_list(struct statistic *, s64, s64, u32);
+extern int statistic_define_raw(struct statistic *, s64, s64, u32);
+extern int statistic_define_history(struct statistic *, s64, s64, u32, u64,
+				    int);
+
+extern int statistic_start(struct statistic *);
+extern int statistic_stop(struct statistic *);
+extern void statistic_reset(struct statistic *);
+
+/**
+ * statistic_add - update statistic with (discriminator, increment) pair
+ * @stat: statistic
+ * @value: discriminator
+ * @incr: increment
+ *
+ * The actual processing of (discriminator, increment) is determined by the
+ * the definition applied to the statistic. See the descriptions of the
+ * statistic_define_*() routines for details.
+ *
+ * This variant grabs the lock and should be used when there is _no_ need
+ * to make a bunch of updates to various statistics of an interface,
+ * including the statistic this update is reported for, atomic
+ * in order to be meaningful (get the next coherent state of several
+ * statistics).
+ *
+ * On success, the return value is dependend on which type of accumulation
+ * has been applied through the recent definition. Usually, returns the
+ * updated total of increments reported for this discriminator, if the
+ * defined type of accumulation does this kind of computation.
+ *
+ * If the struct statistic pointer provided by the caller
+ * is NULL (unused), this routine fails, and 0 is returned.
+ *
+ * If some required memory could not be allocated this routine fails,
+ * and 0 is returned.
+ *
+ * If the discriminator is not valid (out of range), this routine fails,
+ * and 0 is returned.
+ */
+static inline u64 statistic_add(struct statistic *stat, s64 value, u64 incr)
+{
+	unsigned long flags;
+	int retval;
+
+	if (stat->on != STATISTIC_DEF_ON)
+		return 0;
+
+	statistic_lock(stat->interface, flags);
+	retval = stat->add(stat, value, incr);
+	statistic_unlock(stat->interface, flags);
+
+	return retval;
+}
+
+/**
+ * statistic_add_nolock - a statistic_add() variant
+ * @stat: statistic
+ * @value: discriminator
+ * @incr: increment
+ *
+ * Same purpose and behavious as statistic_add(). See there for details.
+ *
+ * Only difference to statistic_add():
+ * Lock management is up to the exploiter. Basically, we give exploiters
+ * the option to ensure data consistency across all statistics attached
+ * to a parent interface by adding several calls to this routine into one
+ * critical section protected by stat->interface->lock,
+ */
+static inline u64 statistic_add_nolock(struct statistic *stat, s64 value,
+				       u64 incr)
+{
+	if (stat->on != STATISTIC_DEF_ON)
+		return 0;
+
+#ifdef DEBUG
+	assert_spin_locked(&stat->interface->lock);
+#endif
+
+	return stat->add(stat, value, incr);
+}
+
+/**
+ * statistic_inc - a statistic_add() variant
+ * @stat: statistic
+ * @value: discriminator
+ *
+ * Same purpose and behaviour as statistic_add(). See there for details.
+ * Difference: Increment defaults to 1.
+ */
+static inline u64 statistic_inc(struct statistic *stat, s64 value)
+{
+	unsigned long flags;
+	int retval;
+
+	if (stat->on != STATISTIC_DEF_ON)
+		return 0;
+
+	statistic_lock(stat->interface, flags);
+	retval = stat->add(stat, value, 1);
+	statistic_unlock(stat->interface, flags);
+
+	return retval;
+}
+
+/**
+ * statistic_inc_nolock - a statistic_add_nolock() variant
+ * @stat: statistic
+ * @value: discriminator
+ *
+ * Same purpose and behaviour as statistic_add_nolock(). See there for details.
+ * Difference: Increment defaults to 1.
+ */
+static inline u64 statistic_inc_nolock(struct statistic *stat, s64 value)
+{
+	if (stat->on != STATISTIC_DEF_ON)
+		return 0;
+
+#ifdef DEBUG
+	assert_spin_locked(&stat->interface->lock);
+#endif
+
+	return stat->add(stat, value, 1);
+}
+
+#else /* CONFIG_STATISTICS */
+
+#define statistic_lock(interface, flags)	do { } while (0)
+#define statistic_unlock(interface, flags)	do { } while (0)
+
+static inline int statistic_interface_create(
+				struct statistic_interface **interface_ptr,
+				const char *name)
+{
+	return 0;
+}
+
+static inline int statistic_interface_remove(
+				struct statistic_interface **interface_ptr)
+{
+	return 0;
+}
+
+static inline int statistic_create(struct statistic **stat_ptr,
+				   struct statistic_interface *interface,
+				   const char *name, const char *units)
+{
+	return 0;
+}
+
+static inline int statistic_remove(struct statistic **stat_ptr)
+{
+	return 0;
+}
+
+
+static inline int statistic_define_value(struct statistic *stat, s64 range_min,
+					 s64 range_max, int mode)
+{
+	return 0;
+}
+
+static inline int statistic_define_range(struct statistic *stat, s64 range_min,
+					 s64 range_max)
+{
+	return 0;
+}
+
+static inline int statistic_define_array(struct statistic *stat, s64 range_min,
+					 s64 range_max, u32 base_interval,
+					 u8 scale)
+{
+	return 0;
+}
+
+static inline int statistic_define_list(struct statistic *stat, s64 range_min,
+					s64 range_max, u32 entries_max)
+{
+	return 0;
+}
+
+static inline int statistic_define_raw(struct statistic *stat, s64 range_min,
+				       s64 range_max, u32 entries_max)
+{
+	return 0;
+}
+
+static inline int statistic_define_history(struct statistic *stat,
+					   s64 range_min, s64 range_max,
+					   u32 entries_max, u64 period,
+					   int mode)
+{
+	return 0;
+}
+
+
+static inline int statistic_start(struct statistic *stat)
+{
+	return 0;
+}
+
+static inline int statistic_stop(struct statistic *stat)
+{
+	return 0;
+}
+
+static inline void statistic_reset(struct statistic *stat)
+{
+}
+
+static inline u64 statistic_add(struct statistic *stat, s64 value, u64 incr)
+{
+	return 0;
+}
+
+static inline u64 statistic_add_nolock(struct statistic *stat, s64 value,
+				       u64 incr)
+{
+	return 0;
+}
+
+static inline u64 statistic_inc(struct statistic *stat, s64 value)
+{
+	return 0;
+}
+
+static inline u64 statistic_inc_nolock(struct statistic *stat, s64 value)
+{
+	return 0;
+}
+
+#endif /* CONFIG_STATISTICS */
+
+#endif /* STATISTIC_H */
diff -Nurp e/lib/Kconfig.statistic f/lib/Kconfig.statistic
--- e/lib/Kconfig.statistic	1970-01-01 01:00:00.000000000 +0100
+++ f/lib/Kconfig.statistic	2005-12-14 14:22:54.000000000 +0100
@@ -0,0 +1,12 @@
+config STATISTICS
+	bool "Statistics infrastructure"
+	depends on DEBUG_FS
+	select SGRB
+	help
+	  The statistics infrastructure provides a debug-fs based user interface
+	  for statistics of kernel components, that is, usually device drivers.
+	  Statistics are available for components that have been instrumented to
+	  feed data into the statistics infrastructure.
+	  This feature is useful for performance measurements or performance
+	  debugging.
+	  If in doubt, say "N".
diff -Nurp e/lib/Makefile f/lib/Makefile
--- e/lib/Makefile	2005-12-14 13:26:51.000000000 +0100
+++ f/lib/Makefile	2005-12-14 14:30:13.000000000 +0100
@@ -47,6 +47,7 @@ obj-$(CONFIG_TEXTSEARCH_FSM) += ts_fsm.o
 obj-$(CONFIG_SWIOTLB) += swiotlb.o

 obj-$(CONFIG_SGRB) += sgrb.o
+obj-$(CONFIG_STATISTICS) += statistic.o

 hostprogs-y	:= gen_crc32table
 clean-files	:= crc32table.h
diff -Nurp e/lib/statistic.c f/lib/statistic.c
--- e/lib/statistic.c	1970-01-01 01:00:00.000000000 +0100
+++ f/lib/statistic.c	2005-12-14 14:22:55.000000000 +0100
@@ -0,0 +1,2183 @@
+/*
+ *  lib/statistic.c
+ *    statistics facility
+ *
+ *    Copyright (C) 2005 IBM Deutschland Entwicklung GmbH,
+ *                       IBM Corporation
+ *
+ *    Author(s): Martin Peschke (mp3@xxxxxxxxxx),
+ *
+ *    Bugreports to: <Linux390@xxxxxxxxxx>
+ *
+ *
+ * This program 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; either version 2, or (at your option)
+ * any later version.
+ *
+ * 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., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ *
+ *    todos:
+ *	- see locking rules; one tbd remaining
+ *	- define a set of agreed names or a naming scheme for
+ *	  consistency and comparability across exploiters
+ *	  (e.g. similar statistic names for latencies of dasd driver
+ *	  and zfcp driver); this entails an agreement about granularities
+ *	  as well (e.g. separate statistic for read/write/no-data commands);
+ *	  a common set of unit strings would be nice then, too, of course
+ *	  (e.g. "seconds", "milliseconds", "microseconds", ...)
+ *	- seq_file use might simplify this code
+ *
+ *
+ *    another bunch of ideas being pondered:
+ *	- provide a (perl?) script for automatic reformating and processing of
+ *	  the contents of "data" files (for generating fancy tables, diagrams
+ *	  in ASCII-art, XML-output ready to be imported into the OpenOffice
+ *	  spreadsheet/diagram tool, ... you name it); a generic script that
+ *	  takes hints from "definition" files into account would basically
+ *	  suffice for all exploiters
+ *	- slim down struct statistic and move on/off/reset/started/stopped
+ *        etc. up to struct statistic_interface???
+ *	  (Is there a need to turn individual statistic on and off etc; or
+ *	  is it more handy and sufficient to allow that only for the entirety
+ *	  of all statistic attached to an interface?)
+ *	- some user-configurable that allows to release unused resources
+ *	  of stopped statistic; or release on stop / allocate on start?
+ *	- perf. opt. of array: table lookup of values, binary search for values
+ *	- another statistic disclipline based on some sort of tree, but
+ *	  similar in semantics to list discipline (for high-perf. histograms of
+ *	  discrete values)
+ *	- use list entries (visible in data file) for hits_out_of_range/
+ *	  hits_missed instead of meta data values (visible in definition file)
+ *	  on analogy to first and last entries of array discipline (<=range_min,
+ *	  >range_max)???
+ *	- allow for more than a single "view" on data at the same time by
+ *	  providing the capability to attach several (a list of) "definitions"
+ *	  to a struct statistic
+ *	  (e.g. show histogram of requests sizes and history of megabytes/sec.
+ *	  at the same time)
+ *	- group similar statitistics in classes and allow for redefinitions
+ *	  per group
+ *	  (e.g. [automagically?] group all list disciplines of request sizes
+ *	  gathered by zfcp in order to allow for a single-operation redefinition
+ *	  of range_max for all of them)
+ *	- multi-dimensional statistic (combination of two or more
+ *	  characteristics/discriminators); worth the effort??
+ *	  (e.g. a matrix of occurences for latencies of requests of
+ *	  particular sizes)
+ *	- allow exploiters to register a callback with every struct statistic
+ *	  (or statistic interface?) in order to be able to do another
+ *	  statitics update when the user reads the data file; would be useful
+ *	  for gathering statistic data about any ongoing condition
+ *	- have exploiters always provide the best granularity possible
+ *	  (like nanoseconds instead of milliseconds) in order to keep
+ *	  flexibility, and have the statitics user interface handle any
+ *	  desired computation (like from nanoseconds to milliseconds)
+ *	- allow user to choose hex/oct/dec representation of numbers
+ *	- make "history" an extra option that allows it to combine with
+ *	  any other type/discipline??? (history request size lists???)
+ *	- split out the definition of range_min/range_max from existing
+ *	  definition functions
+ *
+ *
+ *    locking rules
+ *	- We grab a global semaphore on calls to statistic_interface_create() /
+ *	  statistic_interface_remove() to make sure various exploiters do not
+ *	  interfere with each other by corrupting internal global data (list).
+ *	- Once an interface has been created, it is assumed that the exploiter
+ *	  serialises any other setup or closure business related to statistics
+ *	  attached to the same interface. No internal locking for this purpose!
+ *	- data reading vs. data gathering vs. redefinition (incl. on/off/reset):
+ *	  We hold the interfaces spinlock to make sure that statistics' meta
+ *	  data as well their data is not being messed with concurrently,
+ *	  and coherent on reading (concurrent updates shall not interfere).
+ *	- data gathering vs. removal of statistic: It is assumed that the
+ *	  exploiter makes sure that data gathering has ceased prior to removing
+ *	  a statistic.
+ *	- multiple related data updates in the scope of a single interface:
+ *	  We provide *_nolock variants of the statistic_inc() /
+ *	  statistic_add() routines, and thus allow exploiters to manage
+ *	  locking during updates. This way multiple updates can be made in
+ *	  an atomic fashion. Exploiters are encouraged to make use of this
+ *	  if an atomic update of more than one statistic is required to
+ *	  generate the next valid state as to the coherence of related
+ *	  statistics.
+ *	- touching files by user vs. removal of anything: tbd
+ *
+ *    known bugs:
+ *      - Statistics of type "history" are continuesly updated even if being
+ *	  turned off. Fix: implement statistic_stop_history() and move the
+ *	  beforementioned enforced update - inactivity case - there from
+ *	  statistic_format_data_history().
+ */
+
+#define STATISTIC_C_REVISION "$Revision: 1.5 $"
+
+#include <linux/fs.h>
+#include <linux/debugfs.h>
+#include <linux/module.h>
+#include <linux/list.h>
+#include <linux/parser.h>
+#include <linux/time.h>
+#include <linux/spinlock.h>
+#include <linux/sched.h>
+
+#include <asm/bug.h>
+#include <asm/uaccess.h>
+#include <asm/semaphore.h>
+
+#include <linux/sgrb.h>
+#include <linux/statistic.h>
+
+extern void tod_to_timeval(__u64, struct timespec *);
+
+struct statistic_global_data statistic_globals;
+
+static int statistic_interface_generic_close(struct inode *inode,
+					     struct file *file);
+static ssize_t statistic_interface_generic_read(struct file *, char __user *,
+						size_t, loff_t *);
+static ssize_t statistic_interface_generic_write(struct file *,
+					const char __user *, size_t, loff_t *);
+
+static int statistic_interface_def_open(struct inode *, struct file *);
+static int statistic_interface_def_close(struct inode *, struct file *);
+
+static int statistic_interface_data_open(struct inode *, struct file *);
+
+struct file_operations statistic_def_file_ops = {
+	.owner		= THIS_MODULE,
+	.read		= statistic_interface_generic_read,
+	.write		= statistic_interface_generic_write,
+	.open		= statistic_interface_def_open,
+	.release	= statistic_interface_def_close,
+};
+
+struct file_operations statistic_data_file_ops = {
+	.owner		= THIS_MODULE,
+	.read		= statistic_interface_generic_read,
+	.open		= statistic_interface_data_open,
+	.release	= statistic_interface_generic_close,
+};
+
+/*
+ * FIXME:
+ * Is there any way to get rid of statistic_strings by merging it somehow into
+ * statistic_def?
+ */
+static char * statistic_strings[] = {
+	"name=",
+	"units=",
+	"type=value",
+	"type=range",
+	"type=array",
+	"type=list",
+	"type=raw",
+	"type=history",
+	"on=1",
+	"on=0",
+	"started=",
+	"stopped=",
+	"range_min=",
+	"range_max=",
+	"scale=lin",
+	"scale=log2",
+	"entries_max=",
+	"base_interval=",
+	"hits_missed=",
+	"hits_out_of_range=",
+	"data=",
+	"mode=increments",
+	"mode=products",
+	"mode=range",
+	"period=",
+	NULL
+};
+
+static match_table_t statistic_def = {
+	{STATISTIC_DEF_NAME, "name=%s"},
+	{STATISTIC_DEF_UNIT, "units="},
+	{STATISTIC_DEF_TYPE_VALUE, "type=value"},
+	{STATISTIC_DEF_TYPE_RANGE, "type=range"},
+	{STATISTIC_DEF_TYPE_ARRAY, "type=array"},
+	{STATISTIC_DEF_TYPE_LIST, "type=list"},
+	{STATISTIC_DEF_TYPE_RAW, "type=raw"},
+	{STATISTIC_DEF_TYPE_HISTORY, "type=history"},
+	{STATISTIC_DEF_ON, "on=1"},
+	{STATISTIC_DEF_OFF, "on=0"},
+	{STATISTIC_DEF_STARTED, "started="},
+	{STATISTIC_DEF_STOPPED, "stopped="},
+	{STATISTIC_DEF_RANGEMIN, "range_min=%s"},
+	{STATISTIC_DEF_RANGEMAX, "range_max=%s"},
+	{STATISTIC_DEF_SCALE_LIN, "scale=lin"},
+	{STATISTIC_DEF_SCALE_LOG2, "scale=log2"},
+	{STATISTIC_DEF_ENTRIESMAX, "entries_max=%u"},
+	{STATISTIC_DEF_BASEINT, "base_interval=%s"},
+	{STATISTIC_DEF_HITSMISSED, "hits_missed="},
+	{STATISTIC_DEF_HITSOUT, "hits_out_of_range="},
+	{STATISTIC_DEF_RESET, "data=reset"},
+	{STATISTIC_DEF_MODE_INC, "mode=increments"},
+	{STATISTIC_DEF_MODE_PROD, "mode=products"},
+	{STATISTIC_DEF_MODE_RANGE, "mode=range"},
+	{STATISTIC_DEF_PERIOD, "period=%s"},
+	{STATISTIC_DEF_VOID, NULL}
+};
+
+/* code concerned with module matters */
+
+int __init statistic_init(void)
+{
+	sema_init(&statistic_globals.sem, 1);
+	INIT_LIST_HEAD(&statistic_globals.interface_lh);
+	statistic_globals.root_dir = debugfs_create_dir(STATISTIC_ROOT_DIR, NULL);
+	return 0;
+}
+
+void __exit statistic_exit(void)
+{
+	/*
+	 * FIXME: any need to cleanup any statistic possibly still allocated?
+	 * (would only concern leftovers of exploiters - someone elses problem?)
+	 */
+	debugfs_remove(statistic_globals.root_dir);
+}
+
+/* code mostly concerned with accounting */
+
+static inline int statistic_start_nolock(struct statistic *stat)
+{
+	int retval = stat->on;
+
+	stat->on = STATISTIC_DEF_ON;
+	stat->started = sched_clock();
+
+	return retval;
+}
+
+/**
+ * statistic_start - enable statistic for data gathering
+ * @stat: statistic to be enabled
+ *
+ * Start data gathering without discarding old data.
+ * Function is both available to exploiting device drivers as well as to
+ * the user through the "definition" file.
+ *
+ * On success, returns the previous on/off state.
+ */
+int statistic_start(struct statistic *stat)
+{
+	unsigned long flags;
+	int retval;
+
+	statistic_lock(stat->interface, flags);
+	retval = statistic_start_nolock(stat);
+	statistic_unlock(stat->interface, flags);
+
+	return retval;
+}
+
+static inline int statistic_stop_nolock(struct statistic *stat)
+{
+	int retval = stat->on;
+
+	stat->on = STATISTIC_DEF_OFF;
+	stat->stopped = sched_clock();
+
+	return retval;
+}
+
+/**
+ * statistic_stop - disable statistic for data gathering
+ * @stat: statistic to be disabled
+ *
+ * Stop data gathering without discarding old data.
+ * Function is both available to exploiting device drivers as well as to
+ * the user through the "definition" file.
+ *
+ * On success, returns the previous on/off state.
+ */
+int statistic_stop(struct statistic *stat)
+{
+	unsigned long flags;
+	int retval;
+
+	statistic_lock(stat->interface, flags);
+	retval = statistic_stop_nolock(stat);
+	statistic_unlock(stat->interface, flags);
+
+	return retval;
+}
+
+static inline void statistic_reset_nolock(struct statistic *stat)
+{
+	stat->reset(stat);
+	stat->hits_out_of_range = 0;
+	stat->age = sched_clock();
+}
+
+/**
+ * statistic_reset - discard data gathered so far
+ * @stat: statistic to be reset
+ *
+ * Discard any gathered data without changing the on/off state.
+ * Function is both available to exploiting device drivers as well as to
+ * the user through the "definition" file.
+ */
+void statistic_reset(struct statistic *stat)
+{
+	unsigned long flags;
+
+	statistic_lock(stat->interface, flags);
+	statistic_reset_nolock(stat);
+	statistic_unlock(stat->interface, flags);
+}
+
+/**
+ * statistic_create - create a statistic and attach it to a given interface
+ * @stat_ptr: reference to struct statistic pointer
+ * @interface_ptr: struct statistic_interface pointer
+ * @name: name of statistic to be created and as seen in "data" and
+ *        "definition" files
+ * @units: string describing the units of the (discriminator, value) pairs
+ *	   that are the raw data delivered by the exploiter to
+ *	   the statistics facility for every update to a statistic,
+ *         exported through the definition file for users' information,
+ *	   suggested format "unit1/unit2" (no blanks!)
+ *
+ * Create a statistic, which - after being defined and enabled - is ready
+ * to capture and compute data provided by the exploiter. A line in the
+ * interface's "definition" file will hold specifics about the named statistic.
+ * The statistic is defined as type "value" by default for the convenience
+ * of the statistics code which can now rely on a statistic to have some
+ * valid settings all the time.
+ *
+ * On success, 0 is returned, and the struct statistic pointer
+ * provided by the caller points to a newly allocated struct.
+ *
+ * If the struct statistic pointer provided by the caller
+ * is not NULL (used), this routine fails, the struct statistic
+ * pointer is not changed, and -EINVAL is returned.
+ *
+ * If some required memory could not be allocated this routine fails,
+ * the struct statistic pointer is not changed, and -ENOMEM is returned.
+ */
+int statistic_create(struct statistic **stat_ptr,
+		     struct statistic_interface *interface,
+		     const char *name, const char *units)
+{
+	struct statistic *stat;
+	unsigned long flags;
+
+	if (*stat_ptr || !interface)
+		return -EINVAL;
+
+	stat = kmalloc(sizeof(struct statistic), GFP_KERNEL);
+	if (!stat)
+		return -ENOMEM;
+	memset(stat, 0, sizeof(struct statistic));
+
+	stat->interface = interface;
+	strlcpy(stat->name, name, sizeof(stat->name));
+	strlcpy(stat->units, units, sizeof(stat->units));
+	statistic_define_value(stat, STATISTIC_RANGE_MIN, STATISTIC_RANGE_MAX,
+				STATISTIC_DEF_MODE_INC);
+	statistic_stop_nolock(stat);
+	stat->started = stat->stopped;
+	stat->stat_ptr = stat_ptr;
+
+	statistic_lock(interface, flags);
+	list_add_tail(&stat->list, &interface->statistic_lh);
+	*stat_ptr = stat;
+	statistic_unlock(interface, flags);
+
+	return 0;
+}
+
+/**
+ * statistic_remove - remove given statistic
+ * @stat_ptr: reference to struct statistic pointer
+ *
+ * Remove statistic along with its recent data and definition.
+ *
+ * On success, 0 is returned and the struct statistic pointer
+ * provided by the caller is set to NULL.
+ *
+ * If the struct statistic pointer provided by the caller
+ * is NULL (unused), this routine fails, the struct statistic
+ * pointer is not changed, and -EINVAL is returned.
+ */
+int statistic_remove(struct statistic **stat_ptr)
+{
+	unsigned long flags;
+
+	if (!*stat_ptr)
+		return -EINVAL;
+
+	statistic_lock((*stat_ptr)->interface, flags);
+	if ((*stat_ptr)->release)
+		(*stat_ptr)->release(*stat_ptr);
+	list_del(&(*stat_ptr)->list);
+	kfree(*stat_ptr);
+	*stat_ptr = NULL;
+	statistic_unlock((*stat_ptr)->interface, flags);
+
+	return 0;
+}
+
+static int statistic_format_def(struct statistic *stat,
+				struct statistic_file_private *private)
+{
+	struct sgrb_seg *seg;
+	char t0[TIMESTAMP_SIZE], t1[TIMESTAMP_SIZE], t2[TIMESTAMP_SIZE];
+
+	seg = sgrb_seg_find(&private->read_seg_lh, 1024, GFP_ATOMIC);
+	if (!seg)
+		return -ENOMEM;
+
+	seg->offset += sprintf(seg->address + seg->offset,
+				"%s%s %s %s %s%lld %s%lld",
+				statistic_strings[STATISTIC_DEF_NAME],
+				stat->name,
+				statistic_strings[stat->on],
+				statistic_strings[stat->type],
+				statistic_strings[STATISTIC_DEF_RANGEMIN],
+				(long long signed)stat->range_min,
+				statistic_strings[STATISTIC_DEF_RANGEMAX],
+				(long long signed)stat->range_max);
+
+	if (stat->format_def)
+		seg->offset += stat->format_def(stat,
+						seg->address + seg->offset);
+
+	nsec_to_timestamp(t0, stat->age);
+	nsec_to_timestamp(t1, stat->started);
+	nsec_to_timestamp(t2, stat->stopped);
+
+	seg->offset += sprintf(seg->address + seg->offset,
+				" %s%llu %s%s %s%s %s%s %s%s\n\n",
+				statistic_strings[STATISTIC_DEF_HITSOUT],
+				(long long unsigned)stat->hits_out_of_range,
+				statistic_strings[STATISTIC_DEF_RESET], t0,
+				statistic_strings[STATISTIC_DEF_STARTED], t1,
+				statistic_strings[STATISTIC_DEF_STOPPED], t2,
+				statistic_strings[STATISTIC_DEF_UNIT],
+				stat->units);
+
+	return 0;
+}
+
+/* code concerned with single value statistics */
+
+static void statistic_reset_value(struct statistic *stat)
+{
+	stat->data.value.hits = 0;
+}
+
+static inline void _statistic_format_data_value(struct statistic *stat,
+				struct sgrb_seg *seg, char *s, u64 value)
+{
+	seg->offset += sprintf(seg->address + seg->offset, "%s%s %llu\n",
+				stat->name, s,
+				(unsigned long long)stat->data.value.hits);
+}
+
+static int statistic_format_data_value(struct statistic *stat,
+				       struct statistic_file_private *private)
+{
+	struct sgrb_seg *seg;
+
+	seg = sgrb_seg_find(&private->read_seg_lh, 128, GFP_ATOMIC);
+	if (!seg)
+		return -ENOMEM;
+
+	_statistic_format_data_value(stat, seg, "", stat->data.value.hits);
+	return 0;
+}
+
+static int statistic_format_def_value(struct statistic *stat, char *line)
+{
+	return sprintf(line, " %s", statistic_strings[stat->data.value.mode]);
+}
+
+static inline u64 _statistic_add_value_increments(s64 *single, s64 value,
+						  u64 incr)
+{
+	return (*single += incr);
+}
+
+static inline u64 _statistic_add_value_products(s64 *single, s64 value,
+						u64 incr)
+{
+	if (value < 0)
+		value = -value;
+	return (*single += value * incr);
+}
+
+static u64 statistic_add_value_increments(struct statistic *stat, s64 value,
+					  u64 incr)
+{
+	if (value < stat->range_min || value > stat->range_max) {
+		stat->hits_out_of_range++;
+		return 0;
+	}
+	return _statistic_add_value_increments(
+			&stat->data.value.hits, value, incr);
+}
+
+static u64 statistic_add_value_products(struct statistic *stat, s64 value,
+					u64 incr)
+{
+	if (value < stat->range_min || value > stat->range_max) {
+		stat->hits_out_of_range++;
+		return 0;
+	}
+	return _statistic_add_value_products(
+			&stat->data.value.hits, value, incr);
+}
+
+/**
+ * statistic_define_value - instantiate statistic as single value (counter)
+ * @stat: statistic to be defined
+ * @range_min: lower bound of discriminators
+ * @range_max: upper bound of discriminators
+ * @mode: determines how to use the counter
+ *
+ * Depending on the mode parameter, accumulation is done as
+ *
+ * a) <total> += <increment N>				(mode=increments)
+ * b) <total> += ABS(<discriminator N>) * <increment N>	(mode=products)
+ *
+ * The output format of a single value statistic found in the "data" file is:
+ * <statistic name> <total>
+ *
+ * This (re)definition function is available both to exploiting device drivers
+ * and to the user through the "definition" file. Device driver programmers
+ * might find it user-friendly to provide a default definition for a
+ * particular statistic by calling this or a related function. A previous
+ * definition is replaced by the new one. In addition, the statistic must be
+ * started in order to make it gather data. A line in the interface's "definition"
+ * file holds specifics about the named statistic.
+ *
+ * This routines always succeeds and returns 0.
+ */
+int statistic_define_value(struct statistic *stat, s64 range_min, s64 range_max,
+			   int mode)
+{
+	unsigned long flags;
+
+	if (mode != STATISTIC_DEF_MODE_INC &&
+	    mode != STATISTIC_DEF_MODE_PROD)
+		return -EINVAL;
+
+	statistic_lock(stat->interface, flags);
+
+	if (stat->release)
+		stat->release(stat);
+
+	stat->type = STATISTIC_DEF_TYPE_VALUE;
+	stat->range_min = range_min;
+	stat->range_max = range_max;
+	stat->data.value.mode = mode;
+
+	stat->release = NULL;
+	stat->reset = statistic_reset_value;
+	stat->format_data = statistic_format_data_value;
+	stat->format_def = statistic_format_def_value;
+	if (mode == STATISTIC_DEF_MODE_INC)
+		stat->add = statistic_add_value_increments;
+	else
+		stat->add = statistic_add_value_products;
+
+	statistic_reset_nolock(stat);
+
+	statistic_unlock(stat->interface, flags);
+
+	return 0;
+}
+
+/* code concerned with range statistic */
+
+static inline void statistic_init_range(struct statistic_entry_range *range,
+					s64 range_min, s64 range_max)
+{
+	range->num = 0;
+	range->acc = 0;
+	range->min = range_max + 1;
+	range->max = range_min - 1;
+}
+
+static void statistic_reset_range(struct statistic *stat)
+{
+	statistic_init_range(
+		&stat->data.range.range, stat->range_min, stat->range_max);
+}
+
+static inline void _statistic_format_data_range(struct statistic *stat,
+	struct sgrb_seg *seg, char *s, struct statistic_entry_range *range)
+{
+	long long unsigned whole = 0;
+	long long signed min = 0, max = 0, decimal = 0, last_digit;
+
+	if (range->num) {
+		whole = range->acc;
+		do_div(whole, range->num);
+		decimal  = range->acc * 10000;
+		do_div(decimal, range->num);
+		decimal -= whole * 10000;
+		if (decimal < 0)
+			decimal = -decimal;
+		last_digit = decimal;
+		do_div(last_digit, 10);
+		last_digit = decimal - last_digit * 10;
+		if (last_digit >= 5)
+			decimal += 10;
+		do_div(decimal, 10);
+		min = range->min;
+		max = range->max;
+	}
+
+	seg->offset += sprintf(seg->address + seg->offset,
+				"%s%s %llu %lld %lld.%03lld %lld\n",
+				stat->name, s,
+				(long long unsigned)range->num,
+				(long long signed)min,
+				whole, decimal,
+				(long long signed)max);
+}
+
+static int statistic_format_data_range(struct statistic *stat,
+				       struct statistic_file_private *private)
+{
+	struct sgrb_seg *seg;
+
+	seg = sgrb_seg_find(&private->read_seg_lh, 128, GFP_ATOMIC);
+	if (!seg)
+		return -ENOMEM;
+
+	_statistic_format_data_range(
+		stat, seg, "", &stat->data.range.range);
+	return 0;
+}
+
+static inline u64 _statistic_add_range(struct statistic_entry_range *range,
+				       s64 value, u64 incr)
+{
+	range->num += incr;
+	range->acc += value * incr;
+	if (value < range->min)
+		range->min = value;
+	if (value > range->max)
+		range->max = value;
+	return range->num;
+}
+
+static u64 statistic_add_range(struct statistic *stat, s64 value, u64 incr)
+{
+	if (value < stat->range_min || value > stat->range_max) {
+		stat->hits_out_of_range++;
+		return 0;
+	}
+	return _statistic_add_range(&stat->data.range.range, value, incr);
+}
+
+/**
+ * statistic_define_range - instantiate statistic as small set of values
+ *    that describe a range of observed discriminitors
+ * @stat: statistic to be defined
+ * @range_min: lower bound of discriminators
+ * @range_max: upper bound of discriminators
+ *
+ * Determines that the statistic provides the minimum, average and maximum
+ * of the numbers reported by the exploiter. Besides the number of updates
+ * is counted. Statistic events with increments larger than 1 are counted
+ * as multiple occurences of a particular discrimintator with regard to
+ * the computation of the average.
+ * For example, this statistic type could be used as a fill level or
+ * utilisation indicator for queues.
+ *
+ * The output format of a range statistic found in the "data" file is:
+ * <statistic name> <total of increments> <minimum> <average> <maximum>
+ *
+ * This (re)definition function is available both to exploiting device drivers
+ * and to the user through the "definition" file. Device driver programmers
+ * might find it user-friendly to provide a default definition for a
+ * particular statistic by calling this or a related function. A previous
+ * definition is replaced by the new one. In addition, the statistic must be
+ * started in order to make it gather data. A line in the interface's "definition"
+ * file holds specifics about the named statistic.
+ *
+ * This routine always succeeds and returns 0.
+ */
+int statistic_define_range(struct statistic *stat, s64 range_min, s64 range_max)
+{
+	unsigned long flags;
+
+	statistic_lock(stat->interface, flags);
+
+	if (stat->release)
+		stat->release(stat);
+
+	stat->type = STATISTIC_DEF_TYPE_RANGE;
+	stat->range_min = range_min;
+	stat->range_max = range_max;
+
+	stat->release = NULL;
+	stat->reset = statistic_reset_range;
+	stat->format_data = statistic_format_data_range;
+	stat->format_def = NULL;
+	stat->add = statistic_add_range;
+
+	statistic_reset_nolock(stat);
+
+	statistic_unlock(stat->interface, flags);
+
+	return 0;
+}
+
+/* code concerned with fixed array statistics */
+
+static inline s64 statistic_array_calc_value_lin(struct statistic *stat,
+						 int index)
+{
+	return stat->range_min + (stat->data.array.base_interval * index);
+}
+
+static inline s64 statistic_array_calc_value_log2(struct statistic *stat,
+						  int index)
+{
+	return stat->range_min +
+		(index ? (stat->data.array.base_interval << (index - 1)) : 0);
+}
+
+static inline s64 statistic_array_calc_value(struct statistic *stat, int index)
+{
+	if (stat->data.array.scale == STATISTIC_DEF_SCALE_LIN)
+		return statistic_array_calc_value_lin(stat, index);
+	else
+		return statistic_array_calc_value_log2(stat, index);
+}
+
+static inline int statistic_array_calc_index_lin(struct statistic *stat,
+						 s64 value)
+{
+	unsigned long long index = value - stat->range_min;
+	do_div(index, stat->data.array.base_interval);
+	return index;
+}
+
+static inline int statistic_array_calc_index_log2(struct statistic *stat,
+						  s64 value)
+{
+	unsigned long long index;
+
+	for (index = 0;
+	     index < (stat->data.array.entries - 1) &&
+	     value > statistic_array_calc_value_log2(stat, index);
+	     index++);
+	return index;
+}
+
+static inline int statistic_array_calc_index(struct statistic *stat, s64 value)
+{
+	if (stat->data.array.scale == STATISTIC_DEF_SCALE_LIN)
+		return statistic_array_calc_index_lin(stat, value);
+	else
+		return statistic_array_calc_index_log2(stat, value);
+}
+
+static inline int statistic_alloc_array(struct statistic *stat)
+{
+	int i, size;
+
+	for (i = 0;
+	     statistic_array_calc_value(stat, i) <= stat->range_max;
+	     i++);
+	i++;
+	if (i < 2) {
+		printk("statistic: definition of ""%s"" as type=array failed "
+		       "because it would comprise less than 2 intervals\n",
+		       stat->name);
+		return -EINVAL;
+	}
+	stat->data.array.entries = i;
+
+	size = stat->data.array.entries * sizeof(u64);
+	stat->data.array.hits = kmalloc(size, GFP_KERNEL);
+	if (!stat->data.array.hits) {
+		printk("statistic: definition of ""%s"" as type=array failed "
+		       "due to memory constraints\n", stat->name);
+		return -ENOMEM;
+	}
+	return 0;
+}
+
+static void statistic_release_array(struct statistic *stat)
+{
+	kfree(stat->data.array.hits);
+	stat->data.array.hits = NULL;
+}
+
+static void statistic_reset_array(struct statistic *stat)
+{
+	int size = stat->data.array.entries * sizeof(u64);
+	memset(stat->data.array.hits, 0, size);
+}
+
+static inline int statistic_format_data_array_line(struct statistic *stat,
+					struct statistic_file_private *private,
+					int i, const char *prefix,u64 value)
+{
+	struct sgrb_seg *seg;
+
+	seg = sgrb_seg_find(&private->read_seg_lh, 256, GFP_ATOMIC);
+	if (!seg)
+		return -ENOMEM;
+
+	seg->offset += sprintf(seg->address + seg->offset,
+				"%s %s%lld %llu\n", stat->name,
+				prefix, (long long signed)value,
+				(long long unsigned)stat->data.array.hits[i]);
+	return 0;
+}
+
+static int statistic_format_data_array(struct statistic *stat,
+				       struct statistic_file_private *private)
+{
+	int i;
+	int retval;
+
+	for (i = 0; i < (stat->data.array.entries - 1); i++) {
+		retval = statistic_format_data_array_line(
+				stat, private, i, "<=",
+				statistic_array_calc_value(stat, i));
+		if (retval)
+			return retval;
+	}
+	retval = statistic_format_data_array_line(
+			stat, private, i, ">",
+			statistic_array_calc_value(stat, i - 1));
+	return retval;
+}
+
+static int statistic_format_def_array(struct statistic *stat, char *line)
+{
+	return  sprintf(line,
+			" %s%llu %s",
+			statistic_strings[STATISTIC_DEF_BASEINT],
+			(long long unsigned)stat->data.array.base_interval,
+			statistic_strings[stat->data.array.scale]);
+}
+
+static u64 statistic_add_array_lin(struct statistic *stat, s64 value, u64 incr)
+{
+	int index = statistic_array_calc_index_lin(stat, value);
+	return (stat->data.array.hits[index] += incr);
+}
+
+static u64 statistic_add_array_log2(struct statistic *stat, s64 value, u64 incr)
+{
+	int index = statistic_array_calc_index_log2(stat, value);
+	return (stat->data.array.hits[index] += incr);
+}
+
+/**
+ * statistic_define_array - instantiate statistic as fixed size array of
+ *    interval/counter pairs (histogram for intervals)
+ * @stat: statistic to be defined
+ * @range_min: lower bound of discriminators
+ * @range_max: upper bound of discriminators
+ * @base_interval: width of intervals between two discriminators (linear scale);
+ *         	   starting width of intervals (logarithmic scale, base 2)
+ * @scale: scale applied to discriminators (linear/logarithmic)
+ *
+ * Determines that the statistic maintains a counter for each interval
+ * as determined by the above parameters. These counters hold the total
+ * of the increments applicable to particular intervals. The first interval
+ * is determined by (<the smallest s64 value>, range_min). The last interval
+ * is (range_max, <the largest s64 value>). That means, this statistic
+ * discpline is capable of giving account of hits out of the specified range.
+ * Basically, the function implemented by this statistic discipline is a
+ * histogram for intervals.
+ *
+ * The output format of a fixed-size array statistic found in the "data" file
+ * is:
+ *
+ * <statistic name> "<="<discriminator 0> <total of increments for interval
+ *                                          (smallest s64, discriminator 0)>
+ * <statistic name> "<="<discriminator 1> <total of increments for interval
+ *                                          (discriminator 0, discriminator 1)>
+ * ...
+ * <statistic name> "<="<discriminator N> <total of increments for interval
+ *                                         (discriminator N-1, discriminator N)>
+ * <statistic name> ">"<discriminator N> <total of increments for interval
+ *                                         (discriminator N, largest s64)>
+ *
+ * This (re)definition function is available both to exploiting device drivers
+ * and to the user through the "definition" file. Device driver programmers
+ * might find it user-friendly to provide a default definition for a
+ * particular statistic by calling this or a related function. A previous
+ * definition is replaced by the new one. In addition, the statistic must be
+ * started in order to make it gather data. A line in the interface's "definition"
+ * file holds specifics about the named statistic.
+ *
+ * On success, 0 is returned.
+ *
+ * If some required memory could not be allocated this routine fails,
+ * the previous definition is preserved, and -ENOMEM is returned.
+ *
+ * If an invalid definition has been specified, the definition is not altered,
+ * and -EINVAL is returned.
+ */
+int statistic_define_array(struct statistic *stat, s64 range_min, s64 range_max,
+			   u32 base_interval, u8 scale)
+{
+	unsigned long flags;
+	int retval;
+	struct statistic *tmp;
+
+	if (range_min > range_max)
+		return -EINVAL;
+
+	if (scale != STATISTIC_DEF_SCALE_LIN &&
+	    scale != STATISTIC_DEF_SCALE_LOG2)
+		return -EINVAL;
+
+	tmp = kmalloc(sizeof(struct statistic), GFP_KERNEL);
+	if (!tmp)
+		return -ENOMEM;
+	memcpy(tmp, stat, sizeof(struct statistic));
+
+	tmp->type = STATISTIC_DEF_TYPE_ARRAY;
+	tmp->range_min = range_min;
+	tmp->range_max = range_max;
+	tmp->data.array.base_interval = base_interval;
+	tmp->data.array.scale = scale;
+
+	tmp->release = statistic_release_array;
+	tmp->reset = statistic_reset_array;
+	tmp->format_data = statistic_format_data_array;
+	tmp->format_def = statistic_format_def_array;
+ 	if (scale == STATISTIC_DEF_SCALE_LIN)
+		tmp->add = statistic_add_array_lin;
+ 	else
+		tmp->add = statistic_add_array_log2;
+
+	retval = statistic_alloc_array(tmp);
+	if (retval) {
+		kfree(tmp);
+		return retval;
+	}
+
+	statistic_lock(stat->interface, flags);
+	if (stat->release)
+		stat->release(stat);
+	memcpy(stat, tmp, sizeof(struct statistic));
+	statistic_reset_nolock(stat);
+ 	statistic_unlock(stat->interface, flags);
+
+	kfree(tmp);
+	return 0;
+}
+
+/* code concerned with adaptable list statistics */
+
+static void statistic_release_list(struct statistic *stat)
+{
+	struct statistic_entry_list *entry, *tmp;
+
+	list_for_each_entry_safe(entry, tmp, &stat->data.list.entry_lh, list) {
+		list_del(&entry->list);
+		kfree(entry);
+	}
+}
+
+static void statistic_reset_list(struct statistic *stat)
+{
+	statistic_release_list(stat);
+	stat->data.list.hits_missed = 0;
+	stat->data.list.entries = 0;
+}
+
+static int statistic_format_data_list(struct statistic *stat,
+				      struct statistic_file_private *private)
+{
+	struct sgrb_seg *seg;
+	struct statistic_entry_list *entry;
+
+	list_for_each_entry(entry, &stat->data.list.entry_lh, list) {
+		seg = sgrb_seg_find(&private->read_seg_lh, 256, GFP_ATOMIC);
+		if (!seg)
+			return -ENOMEM;
+		seg->offset += sprintf(seg->address + seg->offset,
+					"%s 0x%llx %llu\n",
+					stat->name,
+					(long long signed)entry->value,
+					(long long unsigned)entry->hits);
+	}
+	return 0;
+}
+
+static int statistic_format_def_list(struct statistic *stat, char *line)
+{
+	return sprintf(line,
+			" %s%u %s%llu",
+			statistic_strings[STATISTIC_DEF_ENTRIESMAX],
+			stat->data.list.entries_max,
+			statistic_strings[STATISTIC_DEF_HITSMISSED],
+			(long long unsigned)stat->data.list.hits_missed);
+}
+
+static inline void statistic_add_list_sort(struct list_head *head,
+					   struct statistic_entry_list *entry)
+{
+	struct statistic_entry_list *sort =
+		list_prepare_entry(entry, head, list);
+
+	list_for_each_entry_continue_reverse(sort, head, list)
+		if (sort->hits >= entry->hits)
+			break;
+	if (sort->list.next != &entry->list &&
+	    (&sort->list == head || sort->hits >= entry->hits))
+		list_move(&entry->list, &sort->list);
+}
+
+static inline int statistic_add_list_new(struct statistic *stat, s64 value,
+					 u64 incr)
+{
+	struct statistic_entry_list *entry;
+
+	if (stat->data.list.entries == stat->data.list.entries_max)
+		return -ENOMEM;
+
+	entry = kmalloc(sizeof(struct statistic_entry_list), GFP_ATOMIC);
+	if (entry) {
+		entry->value = value;
+		entry->hits = incr;
+		stat->data.list.entries++;
+		list_add_tail(&entry->list, &stat->data.list.entry_lh);
+		return 0;
+	} else	return -ENOMEM;
+}
+
+static u64 statistic_add_list(struct statistic *stat, s64 value, u64 incr)
+{
+	struct statistic_entry_list *entry;
+	struct list_head *head = &stat->data.list.entry_lh;
+
+	if (value < stat->range_min || value > stat->range_max) {
+		stat->hits_out_of_range++;
+		return 0;
+	}
+
+	list_for_each_entry(entry, head, list) {
+		if (entry->value == value) {
+			entry->hits += incr;
+			statistic_add_list_sort(head, entry);
+			return entry->hits;
+		}
+	}
+	if (statistic_add_list_new(stat, value, incr)) {
+		stat->data.list.hits_missed++;
+		return 0;
+	} else
+		return incr;
+}
+
+/**
+ * statistic_define_list - instantiate statistic as adaptable-size list of
+ *    discriminator/counter pairs (histogram for discrete values)
+ * @stat: statistic to be defined
+ * @range_min: lower bound of discriminators
+ * @range_max: upper bound of discriminators
+ * @entries_max: limits the list size
+ *
+ * Determines that the statistic maintains a counter for each discrete
+ * discriminator that is reported along with increments by the exploiter.
+ * These counters hold the total of the increments applicable to particular
+ * discriminators. Hits that were out of the specified range, or that would have
+ * required list entries beyond the specified maximum, are discarded and their
+ * numbers are visible through the "definition" file.
+ * Basically, the function implemented by this statistic discipline is a
+ * histogram for discrete values. Which values make it into the histogram is
+ * determined by their order of appearance (first come, first served).
+ *
+ * The output format of an adaptable-size list statistic found in the "data"
+ * file is:
+ *
+ * <statistic name> <discriminator 0> <total of increments for discriminator 0>
+ * <statistic name> <discriminator 1> <total of increments for discriminator 1>
+ * ...
+ * <statistic name> <discriminator N> <total of increments for discriminator N>
+ *
+ * This (re)definition function is available both to exploiting device drivers
+ * and to the user through the "definition" file. Device driver programmers
+ * might find it user-friendly to provide a default definition for a
+ * particular statistic by calling this or a related function. A previous
+ * definition is replaced by the new one. In addition, the statistic must be
+ * started in order to make it gather data. A line in the interface's "definition"
+ * file holds specifics about the named statistic.
+ *
+ * This routine always succeeds and returns 0.
+ */
+int statistic_define_list(struct statistic *stat, s64 range_min, s64 range_max,
+			  u32 entries_max)
+{
+	unsigned long flags;
+
+	statistic_lock(stat->interface, flags);
+
+	if (stat->release)
+		stat->release(stat);
+
+	stat->type = STATISTIC_DEF_TYPE_LIST;
+	stat->range_min = range_min;
+	stat->range_max = range_max;
+	stat->data.list.entries_max = entries_max;
+	INIT_LIST_HEAD(&stat->data.list.entry_lh);
+
+	stat->release = statistic_release_list;
+	stat->reset = statistic_reset_list;
+	stat->format_data = statistic_format_data_list;
+	stat->format_def = statistic_format_def_list;
+	stat->add = statistic_add_list;
+
+	statistic_reset_nolock(stat);
+
+	statistic_unlock(stat->interface, flags);
+
+	return 0;
+}
+
+/* code concerned with raw, timestamped statistic events */
+
+static void statistic_release_raw(struct statistic *stat)
+{
+	sgrb_release(&stat->data.raw.rb);
+}
+
+static void statistic_reset_raw(struct statistic *stat)
+{
+	sgrb_reset(&stat->data.raw.rb);
+	stat->data.raw.next_serial = 0;
+}
+
+static int statistic_format_data_raw(struct statistic *stat,
+				     struct statistic_file_private *private)
+{
+	struct sgrb_seg *seg;
+	struct sgrb_ptr ptr;
+	struct statistic_entry_raw *entry;
+	char t[TIMESTAMP_SIZE];
+
+	sgrb_ptr_copy(&ptr, &stat->data.raw.rb.first);
+	while ((entry = sgrb_consume_nodelete(&stat->data.raw.rb, &ptr))) {
+		seg = sgrb_seg_find(&private->read_seg_lh, 256, GFP_ATOMIC);
+		if (!seg)
+			return -ENOMEM;
+		nsec_to_timestamp(t, entry->clock);
+		seg->offset += sprintf(seg->address + seg->offset,
+					"%s %s %llu %lld %llu\n",
+					stat->name, t,
+					(long long unsigned)entry->serial,
+					(long long signed)entry->value,
+					(long long unsigned)entry->incr);
+	}
+	return 0;
+}
+
+static int statistic_format_def_raw(struct statistic *stat, char *line)
+{
+	return sprintf(line,
+			" %s%u",
+			statistic_strings[STATISTIC_DEF_ENTRIESMAX],
+			stat->data.raw.entries_max);
+}
+
+static u64 statistic_add_raw(struct statistic *stat, s64 value, u64 incr)
+{
+	struct statistic_entry_raw *entry;
+
+	if (value < stat->range_min || value > stat->range_max) {
+		stat->hits_out_of_range++;
+		return 0;
+	}
+
+	entry = sgrb_produce_overwrite(&stat->data.raw.rb);
+
+	entry->clock = sched_clock();
+	entry->serial = stat->data.raw.next_serial++;
+	entry->value = value;
+	entry->incr = incr;
+
+	return incr;
+}
+
+/**
+ * statistic_define_raw - instantiate statistic as a record of incremental
+ *    updates as they have happened (history of statistic events)
+ * @stat: statistic to be defined
+ * @range_min: lower bound of discriminators
+ * @range_max: upper bound of discriminators
+ * @entries_max: maximum number of entries in ringbuffer
+ *
+ * Determines that the statistic does not maintain counters for any increments,
+ * but that it accumulates the reported updates in the form of a history of
+ * these updates. Updates out of the specified range are dropped, though their
+ * total number is readable through the "definition" file. Besides, once the
+ * allocated pages are completely occupied, new entries are written over the
+ * oldest ones (ringbuffer). Each entry is tagged with a unique serial number
+ * and a timestamp. A single entry consumes 32 bytes.
+ * This discipline might be used to relate (seldom) statistic events to other
+ * (debugging?) events, or to do calculations on raw data in user space.
+ *
+ * The output format of a "raw" statistic found in the "data" file is:
+ *
+ * <statistic name> <discriminator> <increment> <serial> <timestamp>
+ *
+ * This (re)definition function is available both to exploiting device drivers
+ * and to the user through the "definition" file. Device driver programmers
+ * might find it user-friendly to provide a default definition for a
+ * particular statistic by calling this or a related function. A previous
+ * definition is replaced by the new one. In addition, the statistic must be
+ * started in order to make it gather data. A line in the interface's "definition"
+ * file holds specifics about the named statistic.
+ *
+ * On success, 0 is returned.
+ *
+ * If some required memory could not be allocated this routine fails,
+ * the previous definition is preserved, and -ENOMEM is returned.
+ */
+int statistic_define_raw(struct statistic *stat, s64 range_min, s64 range_max,
+			 u32 entries_max)
+{
+	unsigned long flags;
+	int retval;
+	struct statistic *tmp;
+
+	tmp = kmalloc(sizeof(struct statistic), GFP_KERNEL);
+	if (!tmp)
+		return -ENOMEM;
+	memcpy(tmp, stat, sizeof(struct statistic));
+
+	tmp->type = STATISTIC_DEF_TYPE_RAW;
+	tmp->range_min = range_min;
+	tmp->range_max = range_max;
+	tmp->data.raw.entries_max = entries_max;
+
+	tmp->release = statistic_release_raw;
+	tmp->reset = statistic_reset_raw;
+	tmp->format_data = statistic_format_data_raw;
+	tmp->format_def = statistic_format_def_raw;
+	tmp->add = statistic_add_raw;
+
+	tmp->data.raw.next_serial = 0;
+	/*
+	 * sgrb_alloc initialises list head for us. We must not use pointers
+	 * to the stat's list through tmp in order to avoid list corruption.
+	 */
+	retval = sgrb_alloc(&tmp->data.raw.rb,
+			    sizeof(struct statistic_entry_raw),
+			    tmp->data.raw.entries_max, PAGE_SIZE, GFP_KERNEL);
+	if (retval) {
+		printk("statistic: definition of ""%s"" failed due to memory "
+		       "constraints\n", stat->name);
+		kfree(tmp);
+		return retval;
+	}
+
+	statistic_lock(stat->interface, flags);
+	if (stat->release)
+		stat->release(stat);
+	memcpy(stat, tmp, sizeof(struct statistic));
+	/*
+	 * The new ringbuffer's list is attached to tmp. memcpy() has left
+	 * some loose ends pointing to the soon to be kfree()-ed tmp.
+	 * So we need to migrate the list from tmp to stat here,
+	 * even if this looks like nasty poking inside ringbuffers.
+	 */
+	INIT_LIST_HEAD(&stat->data.raw.rb.seg_lh);
+	list_splice(&tmp->data.raw.rb.seg_lh, &stat->data.raw.rb.seg_lh);
+	statistic_reset_nolock(stat);
+ 	statistic_unlock(stat->interface, flags);
+
+	kfree(tmp);
+	return 0;
+}
+
+/* code concerned with history statistics */
+
+static void statistic_release_history(struct statistic *stat)
+{
+	sgrb_release(&stat->data.history.rb);
+}
+
+static void statistic_reset_history(struct statistic *stat)
+{
+	sgrb_reset(&stat->data.history.rb);
+	stat->data.history.checkpoint = sched_clock();
+}
+
+static inline void * statistic_add_history_entry(struct statistic *stat)
+{
+	u64 now, then, window, period, checkp, elapsed;
+	void *entry = NULL;
+
+	window = stat->data.history.window;
+	period = stat->data.history.period;
+	checkp = stat->data.history.checkpoint;
+
+	now = sched_clock();
+	if (now <= checkp)
+		entry = sgrb_entry(&stat->data.history.rb.last);
+	else	{
+		then = checkp;
+		elapsed = now - then;
+		/*
+		 * FIXME: replace loops by formula for supposedly
+		 * improved performance
+		 *  - would require something like do_div64_64()
+		 */
+#if 0
+		if (elapsed > window)
+			then = (now - window) + (period - elapsed % period);
+#endif
+
+		if (elapsed > window) {
+			for (; then < now - 2 * window; then += window);
+			for (; then < now - window; then += period);
+		}
+		for (; then < now; then += period) {
+			entry = sgrb_produce_overwrite(&stat->data.history.rb);
+			memset(entry, 0, stat->data.history.rb.entry_size);
+		}
+		if (stat->data.history.mode == STATISTIC_DEF_MODE_RANGE)
+			statistic_init_range(
+				(struct statistic_entry_range *)entry,
+				stat->range_min,
+				stat->range_max);
+		stat->data.history.checkpoint = then;
+	}
+	return entry;
+}
+
+static inline int statistic_format_data_history(struct statistic *stat,
+					struct statistic_file_private *private)
+{
+	struct sgrb_seg *seg;
+	struct sgrb_ptr ptr;
+	void *entry;
+	u64 time;
+	char t[TIMESTAMP_SIZE + 1];
+
+	/* enforce update for time of inactivity */
+	statistic_add_history_entry(stat);
+	time = stat->data.history.checkpoint -
+	       stat->data.history.period *
+			(stat->data.history.rb.entries - 1);
+	sgrb_ptr_copy(&ptr, &stat->data.history.rb.first);
+	while ((entry = sgrb_consume_nodelete(&stat->data.history.rb, &ptr))) {
+		seg = sgrb_seg_find(&private->read_seg_lh, 256, GFP_ATOMIC);
+		if (!seg)
+			return -ENOMEM;
+		t[0] = ' ';
+		nsec_to_timestamp(&t[1], time);
+		switch (stat->data.history.mode) {
+		case STATISTIC_DEF_MODE_INC :
+		case STATISTIC_DEF_MODE_PROD :
+			_statistic_format_data_value(
+				stat, seg, t, *(u64*)entry);
+			break;
+		case STATISTIC_DEF_MODE_RANGE :
+			_statistic_format_data_range(
+				stat, seg, t,
+				(struct statistic_entry_range *)entry);
+			break;
+		default :
+			break;
+		}
+		time += stat->data.history.period;
+	}
+	return 0;
+}
+
+static inline int statistic_format_def_history(struct statistic *stat,
+					       char *line)
+{
+	unsigned long long period = stat->data.history.period;
+
+	do_div(period, 1000);
+	return sprintf(line,
+			" %s%u %s %s%llu",
+			statistic_strings[STATISTIC_DEF_ENTRIESMAX],
+			stat->data.history.entries_max,
+	    		statistic_strings[stat->data.history.mode],
+			statistic_strings[STATISTIC_DEF_PERIOD],
+			period);
+}
+
+static u64 statistic_add_history_increments(struct statistic *stat, s64 value,
+					    u64 incr)
+{
+	if (value < stat->range_min || value > stat->range_max) {
+		stat->hits_out_of_range++;
+		return 0;
+	}
+	return _statistic_add_value_increments(
+			(s64*) statistic_add_history_entry(stat), value, incr);
+}
+
+static u64 statistic_add_history_products(struct statistic *stat, s64 value,
+					  u64 incr)
+{
+	if (value < stat->range_min || value > stat->range_max) {
+		stat->hits_out_of_range++;
+		return 0;
+	}
+	return _statistic_add_value_products(
+			(s64*) statistic_add_history_entry(stat), value, incr);
+}
+
+static u64 statistic_add_history_range(struct statistic *stat, s64 value,
+				       u64 incr)
+{
+	if (value < stat->range_min || value > stat->range_max) {
+		stat->hits_out_of_range++;
+		return 0;
+	}
+	return _statistic_add_range(
+			(struct statistic_entry_range *)
+				statistic_add_history_entry(stat),
+			value, incr);
+}
+
+/**
+ * statistic_define_history - instantiate statistic as a history
+ *    that accumulates all updates per defined period of time
+ * @stat: statistic to be defined
+ * @range_min: lower bound of discriminators
+ * @range_max: upper bound of discriminators
+ * @entries_max: number of entries in the history buffer
+ * @period: time to elapse for each entry in history
+ * @mode: accumulate increments only, or products of discriminator and increment
+ *
+ * Determines that the statistic does maintain data per fixed period
+ * of time. All updates within a particular period of time are added up. When
+ * that period has passed, the next entry in the history buffer is used to start
+ * over with accumulation. The history buffer is a ringbuffer. That is, the
+ * oldest entry is replaced by the newest, if the history buffer has been filled
+ * up. Updates out of the specified range are dropped, though their total number
+ * is readable through the "definition" file. Each entry is tagged with a
+ * timestamp. Each entry consumes 8 bytes (mode=increments, mode=products)
+ * or 32 bytes (mode=range).
+ * This statistic discipline basically is other basic discplines enhanced by
+ * another dimension, time.
+ *
+ * Depending on the definition, accumulation is done as
+ *
+ * a) mode=increments	: see statistic_define_value()
+ * b) mode=products	: see statistic_define_value()
+ * c) mode=range	: see statistic_define_range()
+ *
+ * The output format of a "history" statistic found in the "data" file is
+ * similar to those documented for the underlying basic types (see mode
+ * parameter), with the exception of a timestamp inserted after the
+ * <statistic name> field that allows to identify an entries of particular
+ * age (timestamp marks the end of periods).
+ *
+ * This (re)definition function is available both to exploiting device drivers
+ * and to the user through the "definition" file. Device driver programmers
+ * might find it user-friendly to provide a default definition for a
+ * particular statistic by calling this or a related function. A previous
+ * definition is replaced by the new one. In addition, the statistic must be
+ * started in order to make it gather data. A line in the interface's "definition"
+ * file holds specifics about the named statistic.
+ *
+ * On success, 0 is returned.
+ *
+ * If some required memory could not be allocated this routine fails,
+ * the previous definition is preserved, and -ENOMEM is returned.
+ *
+ * If an invalid definition has been specified, the definition is not altered,
+ * and -EINVAL is returned.
+ */
+int statistic_define_history(struct statistic *stat, s64 range_min,
+		     s64 range_max, u32 entries_max, u64 period, int mode)
+{
+	unsigned long flags;
+	int retval;
+	struct statistic *tmp;
+	int entry_size;
+
+ 	if (mode != STATISTIC_DEF_MODE_INC &&
+ 	    mode != STATISTIC_DEF_MODE_PROD &&
+ 	    mode != STATISTIC_DEF_MODE_RANGE)
+ 		return -EINVAL;
+
+	tmp = kmalloc(sizeof(struct statistic), GFP_KERNEL);
+	if (!tmp)
+		return -ENOMEM;
+	memcpy(tmp, stat, sizeof(struct statistic));
+
+ 	period *= 1000;	/* microseconds to nanoseconds */
+
+	tmp->type = STATISTIC_DEF_TYPE_HISTORY;
+	tmp->range_min = range_min;
+	tmp->range_max = range_max;
+	tmp->data.history.entries_max = entries_max;
+	tmp->data.history.mode = mode;
+	tmp->data.history.period = period;
+	tmp->data.history.window = entries_max * period;
+
+	tmp->release = statistic_release_history;
+	tmp->reset = statistic_reset_history;
+	tmp->format_data = statistic_format_data_history;
+	tmp->format_def = statistic_format_def_history;
+ 	if (mode == STATISTIC_DEF_MODE_INC)
+		tmp->add = statistic_add_history_increments;
+ 	else if (mode == STATISTIC_DEF_MODE_PROD)
+		tmp->add = statistic_add_history_products;
+ 	else
+		tmp->add = statistic_add_history_range;
+
+	entry_size = (STATISTIC_DEF_MODE_RANGE ?
+		      sizeof(struct statistic_entry_range) :
+		      sizeof(s64));
+	/*
+	 * sgrb_alloc initialises list head for us. We must not use pointers
+	 * to the stat's list through tmp in order to avoid list corruption.
+	 */
+	retval = sgrb_alloc(&tmp->data.history.rb, entry_size,
+			    tmp->data.history.entries_max,
+			    PAGE_SIZE, GFP_KERNEL);
+	if (retval) {
+		printk("statistic: definition of ""%s"" failed due to memory "
+		       "constraints\n", stat->name);
+		kfree(tmp);
+		return retval;
+	}
+
+	statistic_lock(stat->interface, flags);
+	if (stat->release)
+		stat->release(stat);
+	memcpy(stat, tmp, sizeof(struct statistic));
+	/*
+	 * The new ringbuffer's list is attached to tmp. memcpy() has left
+	 * some loose ends pointing to the soon to be kfree()-ed tmp.
+	 * So we need to migrate the list from tmp to stat here,
+	 * even if this looks like nasty poking inside ringbuffers.
+	 */
+	INIT_LIST_HEAD(&stat->data.history.rb.seg_lh);
+	list_splice(&tmp->data.history.rb.seg_lh,
+		    &stat->data.history.rb.seg_lh);
+	statistic_reset_nolock(stat);
+ 	statistic_unlock(stat->interface, flags);
+
+	kfree(tmp);
+	return 0;
+}
+
+/* code concerned with user interface */
+
+/**
+ * statistic_interface_create - create debugfs files for a collection of
+ *    related statistics
+ * @interface_ptr: reference to struct statistic_interface pointer
+ * @name: name of debugfs directory to be created
+ *
+ * Create a debugfs directory in "statistics" as well as the "data" and
+ * "definition" files. Creating this user interface is prequisite for
+ * attaching statistics to an interface.
+ *
+ * On success, 0 is returned and the struct statistic_interface pointer
+ * provided by the caller points to a newly allocated struct.
+ *
+ * If the struct statistic_interface pointer provided by the caller
+ * is not NULL (used), this routine fails, the struct statistic_interface
+ * pointer is not changed, and -EINVAL is returned.
+ *
+ * If some required memory could not be allocated, or the creation
+ * of debugfs entries failed, this routine fails, the struct
+ * statistic_interface pointer is not changed, and -ENOMEM is returned.
+ */
+int statistic_interface_create(struct statistic_interface **interface_ptr,
+			       const char *name)
+{
+	struct statistic_interface *interface;
+	int retval;
+
+	if (*interface_ptr)
+		return -EINVAL;
+
+	interface = kmalloc(sizeof(struct statistic_interface), GFP_KERNEL);
+	if (!interface)
+		return -ENOMEM;
+	memset(interface, 0, sizeof(struct statistic_interface));
+	INIT_LIST_HEAD(&interface->statistic_lh);
+	spin_lock_init(&interface->lock);
+
+	down(&statistic_globals.sem);
+
+	interface->debugfs_dir = debugfs_create_dir(
+					name, statistic_globals.root_dir);
+	if (!interface->debugfs_dir) {
+		retval = -ENOMEM;
+		goto failed_dir;
+	}
+
+	interface->data_file = debugfs_create_file(
+					STATISTIC_FILENAME_DATA,
+					S_IFREG | S_IRUSR,
+					interface->debugfs_dir,
+					(void*) interface,
+					&statistic_data_file_ops);
+	if (!interface->data_file) {
+		retval = -ENOMEM;
+		goto failed_data;
+	}
+
+	interface->def_file = debugfs_create_file(
+					STATISTIC_FILENAME_DEF,
+					S_IFREG | S_IRUSR | S_IWUSR,
+					interface->debugfs_dir,
+					(void*) interface,
+					&statistic_def_file_ops);
+	if (!interface->def_file) {
+		retval = -ENOMEM;
+		goto failed_def;
+	}
+
+	list_add_tail(&interface->list, &statistic_globals.interface_lh);
+	*interface_ptr = interface;
+	retval = 0;
+	goto out;
+
+failed_def:
+	debugfs_remove(interface->data_file);
+
+failed_data:
+failed_dir:
+	kfree(interface);
+	interface = NULL;
+
+out:
+	up(&statistic_globals.sem);
+
+	return retval;
+}
+
+/**
+ * statistic_interface_remove - remove debugfs files for statistics
+ * @interface_ptr: reference to struct statistic_interface pointer
+ *
+ * Remove a debugfs directory in "statistics" along with its "data" and
+ * "definition" files. Removing this user interface also causes the removal
+ * of all statistics attached to the interface.
+ *
+ * On success, 0 is returned and the struct statistic_interface pointer
+ * provided by the caller is set to NULL.
+ *
+ * If the struct statistic_interface pointer provided by the caller
+ * is NULL (unused), this routine fails, the struct statistic_interface
+ * pointer is not changed, and -EINVAL is returned.
+ */
+int statistic_interface_remove(struct statistic_interface **interface_ptr)
+{
+	struct statistic_interface *interface = *interface_ptr;
+	struct statistic *stat, *tmp;
+
+	if (!interface)
+		return -EINVAL;
+
+	down(&statistic_globals.sem);
+
+	list_for_each_entry_safe(stat, tmp, &interface->statistic_lh, list)
+		statistic_remove(stat->stat_ptr);
+
+	debugfs_remove(interface->data_file);
+	debugfs_remove(interface->def_file);
+	debugfs_remove(interface->debugfs_dir);
+
+	list_del(&interface->list);
+	kfree(interface);
+	*interface_ptr = NULL;
+
+	up(&statistic_globals.sem);
+
+	return 0;
+}
+
+static int statistic_interface_generic_open(struct inode *inode,
+		struct file *file, struct statistic_interface **interface,
+		struct statistic_file_private **private)
+{
+	*interface = (struct statistic_interface *) inode->u.generic_ip;
+	BUG_ON(!interface);
+
+	*private = kmalloc(sizeof(struct statistic_file_private), GFP_KERNEL);
+	if (!(*private))
+		return -ENOMEM;
+
+	memset(*private, 0, sizeof(struct statistic_file_private));
+	INIT_LIST_HEAD(&(*private)->read_seg_lh);
+	INIT_LIST_HEAD(&(*private)->write_seg_lh);
+	file->private_data = *private;
+	return 0;
+}
+
+static int statistic_interface_generic_close(struct inode *inode,
+					     struct file *file)
+{
+	struct statistic_file_private *private;
+
+	private = (struct statistic_file_private *) file->private_data;
+	BUG_ON(!private);
+
+	sgrb_seg_release_all(&private->read_seg_lh);
+	sgrb_seg_release_all(&private->write_seg_lh);
+
+	kfree(private);
+	return 0;
+}
+
+static ssize_t statistic_interface_generic_read(struct file *file,
+				char __user *buf, size_t len, loff_t *offset)
+{
+	struct statistic_file_private *private;
+	struct sgrb_seg *seg;
+	size_t seg_offset, seg_residual, seg_transfer;
+	size_t transfered = 0;
+	loff_t pos = 0;
+
+	private = (struct statistic_file_private *) file->private_data;
+	BUG_ON(!private);
+
+	list_for_each_entry(seg, &private->read_seg_lh, list) {
+		if (!len)
+			break;
+		if (*offset >= pos  &&
+		    *offset <= (pos + seg->offset)) {
+			seg_offset = *offset - pos;
+			seg_residual = seg->offset - seg_offset;
+			seg_transfer = min(len, seg_residual);
+			if (copy_to_user(buf + transfered,
+					 seg->address + seg_offset,
+					 seg_transfer))
+				return -EFAULT;
+			transfered += seg_transfer;
+			*offset += seg_transfer;
+			pos += seg_transfer + seg_offset;
+			len -= seg_transfer;
+		} else
+			pos += seg->offset;
+	}
+	return transfered;
+}
+
+static ssize_t statistic_interface_generic_write(struct file *file,
+			const char __user *buf, size_t len, loff_t *offset)
+{
+	struct statistic_file_private *private;
+	struct sgrb_seg *seg;
+	size_t seg_residual, seg_transfer;
+	size_t transfered = 0;
+
+	private = (struct statistic_file_private *) file->private_data;
+	BUG_ON(!private);
+
+	if (*offset != private->write_seg_total_size)
+		return -EPIPE;
+
+	while (len) {
+		seg = sgrb_seg_find(&private->write_seg_lh, 1, GFP_KERNEL);
+		if (!seg)
+			return -ENOMEM;
+		seg_residual = seg->size - seg->offset;
+		seg_transfer = min(len, seg_residual);
+		if (copy_from_user(seg->address + seg->offset,
+				   buf + transfered,
+				   seg_transfer))
+			return -EFAULT;
+		private->write_seg_total_size += seg_transfer;
+		seg->offset += seg_transfer;
+		transfered += seg_transfer;
+		*offset += seg_transfer;
+		len -= seg_transfer;
+	}
+	return transfered;
+}
+
+static int statistic_interface_def_open(struct inode *inode, struct file *file)
+{
+	struct statistic_interface *interface;
+	struct statistic_file_private *private;
+	struct statistic *stat;
+	unsigned long flags;
+	int retval = 0;
+
+	retval = statistic_interface_generic_open(
+			inode, file, &interface, &private);
+	if (retval)
+		return retval;
+
+	statistic_lock(interface, flags);
+	list_for_each_entry(stat, &interface->statistic_lh, list) {
+		retval = statistic_format_def(stat, private);
+		if (retval) {
+			statistic_interface_def_close(inode, file);
+			break;
+		}
+	}
+	statistic_unlock(interface, flags);
+	return retval;
+}
+
+static int statistic_parse_definitions_line(
+			struct statistic_interface *interface, char *def)
+{
+	struct statistic *stat;
+	char * p;
+	substring_t args[MAX_OPT_ARGS];
+	int token, type = 0, scale = 0;
+	u32 entries_max, base_interval;
+	s64 range_min, range_max;
+	u64 period = 0;
+	int mode = 0;
+	char *name = NULL;
+	int retval = 0;
+	unsigned long flags;
+	int got_type = 0, got_scale = 0, got_entries_max = 0,
+	    got_range_min = 0, got_range_max = 0,
+	    got_base_interval = 0, got_period = 0, got_mode = 0, got_reset = 0,
+	    got_on = 0, got_off = 0, redefinition = 0, new_type = 0,
+	    was_on = 0;
+
+	if (!def)
+		return 1;
+
+	while ((p = strsep (&def, " ")) != NULL) {
+		token = match_token(p, statistic_def, args);
+		switch (token) {
+		case STATISTIC_DEF_NAME :
+			if (!name)
+				name = match_strdup(&args[0]);
+			break;
+		case STATISTIC_DEF_TYPE_VALUE :
+		case STATISTIC_DEF_TYPE_RANGE :
+		case STATISTIC_DEF_TYPE_ARRAY :
+		case STATISTIC_DEF_TYPE_LIST :
+		case STATISTIC_DEF_TYPE_RAW :
+		case STATISTIC_DEF_TYPE_HISTORY :
+			type = token;
+			got_type = 1;
+			break;
+		case STATISTIC_DEF_ON :
+			got_on = 1;
+			break;
+		case STATISTIC_DEF_OFF :
+			got_off = 1;
+			break;
+		case STATISTIC_DEF_SCALE_LIN :
+		case STATISTIC_DEF_SCALE_LOG2 :
+			scale = token;
+			got_scale = 1;
+			break;
+		case STATISTIC_DEF_ENTRIESMAX :
+			match_int(&args[0], &entries_max);
+			got_entries_max = 1;
+			break;
+		case STATISTIC_DEF_RANGEMIN :
+			match_s64(&args[0], &range_min, 0);
+			got_range_min = 1;
+			break;
+		case STATISTIC_DEF_RANGEMAX :
+			match_s64(&args[0], &range_max, 0);
+			got_range_max = 1;
+			break;
+		case STATISTIC_DEF_BASEINT :
+			match_int(&args[0], &base_interval);
+			got_base_interval = 1;
+			break;
+		case STATISTIC_DEF_PERIOD :
+			match_u64(&args[0], &period, 0);
+			got_period = 1;
+			break;
+		case STATISTIC_DEF_MODE_INC :
+		case STATISTIC_DEF_MODE_PROD :
+		case STATISTIC_DEF_MODE_RANGE :
+			mode = token;
+			got_mode = 1;
+			break;
+		case STATISTIC_DEF_RESET :
+			got_reset = 1;
+			break;
+		default :
+			break;
+		}
+	}
+
+	redefinition =  got_type | got_mode | got_scale | got_entries_max |
+			got_range_min | got_range_max |
+			got_base_interval | got_period;
+
+	if (!name) {
+		if (redefinition)
+			goto out;
+		statistic_lock(interface, flags);
+		if (got_on)
+			list_for_each_entry(stat, &interface->statistic_lh, list)
+				statistic_start_nolock(stat);
+		if (got_off)
+			list_for_each_entry(stat, &interface->statistic_lh, list)
+				statistic_stop_nolock(stat);
+		if (got_reset) {
+			list_for_each_entry(stat, &interface->statistic_lh, list)
+				statistic_reset_nolock(stat);
+		}
+		statistic_unlock(interface, flags);
+		goto out;
+	}
+
+	statistic_lock(interface, flags);
+	list_for_each_entry(stat, &interface->statistic_lh, list) {
+		if (!strcmp(stat->name, name))
+			break;
+	}
+	statistic_unlock(interface, flags);
+	if (strcmp(stat->name, name))
+		goto out;
+
+	if (!redefinition) {
+		if (got_on)
+			statistic_start(stat);
+		if (got_off)
+			statistic_stop(stat);
+		if (got_reset)
+			statistic_reset(stat);
+		goto out;
+	}
+
+	if (statistic_stop(stat) == STATISTIC_DEF_ON)
+		was_on = 1;
+
+	if (!got_type)
+		type = stat->type;
+	else if (type != stat->type)
+		new_type = 1;
+
+	if (!got_range_min)
+		range_min = stat->range_min;
+	if (!got_range_max)
+		range_max = stat->range_max;
+
+        switch (type) {
+        case STATISTIC_DEF_TYPE_VALUE :
+		if (new_type && !got_mode) {
+			retval = -EINVAL;
+			break;
+		}
+		if (!got_mode)
+			mode = stat->data.value.mode;
+		retval = statistic_define_value(
+				stat, range_min, range_max, mode);
+		break;
+        case STATISTIC_DEF_TYPE_RANGE :
+		retval = statistic_define_range(
+				stat, range_min, range_max);
+		break;
+        case STATISTIC_DEF_TYPE_ARRAY :
+		if (new_type && (!got_base_interval || !got_scale)) {
+			retval = -EINVAL;
+			break;
+		}
+		if (!got_base_interval)
+			base_interval = stat->data.array.base_interval;
+		if (!got_scale)
+			scale = stat->data.array.scale;
+		retval = statistic_define_array(
+				stat, range_min, range_max, base_interval, scale);
+		break;
+        case STATISTIC_DEF_TYPE_LIST :
+		if (new_type && !got_entries_max) {
+			retval = -EINVAL;
+			break;
+		}
+		if (!got_entries_max)
+			entries_max = stat->data.list.entries_max;
+		retval = statistic_define_list(
+				stat, range_min, range_max, entries_max);
+		break;
+        case STATISTIC_DEF_TYPE_RAW :
+		if (new_type && !got_entries_max) {
+			retval = -EINVAL;
+			break;
+		}
+		if (!got_entries_max)
+			entries_max = stat->data.raw.entries_max;
+		retval = statistic_define_raw(
+				stat, range_min, range_max, entries_max);
+		break;
+        case STATISTIC_DEF_TYPE_HISTORY :
+		if (new_type && (!got_entries_max || !got_period ||
+				 !got_mode)) {
+			retval = -EINVAL;
+			break;
+		}
+		if (!got_entries_max)
+			entries_max = stat->data.history.entries_max;
+		if (!got_period)
+			period = stat->data.history.period;
+		if (!got_mode)
+			mode = stat->data.history.mode;
+		retval = statistic_define_history(
+				stat, range_min, range_max, entries_max,
+				period, mode);
+		break;
+        default :
+                retval = -EINVAL;
+        }
+
+	if (got_on || was_on)
+		statistic_start(stat);
+
+out:
+	kfree(name);
+	return retval;
+}
+
+static void statistic_interface_def_close_parse(
+				struct statistic_interface *interface,
+				struct list_head *line_lh, size_t *line_size)
+{
+	struct sgrb_seg *seg, *tmp;
+	char *buf;
+	int offset = 0;
+
+	if (!*line_size)
+		return;
+
+	buf = kmalloc(*line_size + 2, GFP_KERNEL);
+	if (!buf)
+		/*
+		 * FIXME:
+		 * Does it make sense to indicate -ENOMEM on close()?
+		 * Should we omit other new settings because we could not
+		 * process this line of definitions?
+		 */
+		return;
+	buf[*line_size] = ' ';
+	buf[*line_size + 1] = '\0';
+	*line_size = 0;
+
+	list_for_each_entry_safe(seg, tmp, line_lh, list) {
+		memcpy(buf + offset, seg->address, seg->size);
+		offset += seg->size;
+		list_del(&seg->list);
+		kfree(seg);
+	}
+
+	statistic_parse_definitions_line(interface, buf);
+
+	kfree(buf);
+}
+
+static int statistic_interface_def_close(struct inode *inode, struct file *file)
+{
+	struct statistic_interface *interface;
+	struct statistic_file_private *private;
+	struct sgrb_seg *seg, *seg_nl;
+	int offset;
+	struct list_head line_lh;
+	char *nl;
+	size_t line_size = 0;
+
+	INIT_LIST_HEAD(&line_lh);
+	interface = (struct statistic_interface *) inode->u.generic_ip;
+	private = (struct statistic_file_private *) file->private_data;
+
+	list_for_each_entry(seg, &private->write_seg_lh, list) {
+		for (offset = 0; offset < seg->offset; offset += seg_nl->size) {
+			seg_nl = kmalloc(sizeof(struct sgrb_seg), GFP_KERNEL);
+			if (!seg_nl)
+				/*
+				 * FIXME:
+				 * Should we omit other new settings because we
+				 * could not process this line of definitions?
+				 */
+				continue;
+			seg_nl->address = seg->address + offset;
+			nl = strnchr(seg_nl->address,
+				     seg->offset - offset, '\n');
+			if (nl) {
+				seg_nl->offset = nl - seg_nl->address;
+				if (seg_nl->offset)
+					seg_nl->offset--;
+			} else
+				seg_nl->offset = seg->offset - offset;
+			seg_nl->size = seg_nl->offset + 1;
+			line_size += seg_nl->size;
+			list_add_tail(&seg_nl->list, &line_lh);
+			if (nl)
+				statistic_interface_def_close_parse(
+					interface, &line_lh, &line_size);
+		}
+	}
+	if (!list_empty(&line_lh))
+		statistic_interface_def_close_parse(
+			interface, &line_lh, &line_size);
+
+	return statistic_interface_generic_close(inode, file);
+}
+
+static int statistic_interface_data_open(struct inode *inode, struct file *file)
+{
+	struct statistic_interface *interface;
+	struct statistic_file_private *private;
+	struct statistic *stat;
+	unsigned long flags;
+	int retval = 0;
+
+	retval = statistic_interface_generic_open(
+			inode, file, &interface, &private);
+	if (retval)
+		return retval;
+
+	statistic_lock(interface, flags);
+	list_for_each_entry(stat, &interface->statistic_lh, list) {
+		if (stat->format_data) {
+			retval = stat->format_data(stat, private);
+			if (retval) {
+				statistic_interface_generic_close(inode, file);
+				break;
+			}
+		}
+	}
+	statistic_unlock(interface, flags);
+
+	return retval;
+}
+
+postcore_initcall(statistic_init);
+module_exit(statistic_exit);
+MODULE_LICENSE("GPL");
+
+EXPORT_SYMBOL_GPL(statistic_interface_create);
+EXPORT_SYMBOL_GPL(statistic_interface_remove);
+EXPORT_SYMBOL_GPL(statistic_create);
+EXPORT_SYMBOL_GPL(statistic_remove);
+EXPORT_SYMBOL_GPL(statistic_define_value);
+EXPORT_SYMBOL_GPL(statistic_define_range);
+EXPORT_SYMBOL_GPL(statistic_define_array);
+EXPORT_SYMBOL_GPL(statistic_define_list);
+EXPORT_SYMBOL_GPL(statistic_define_raw);
+EXPORT_SYMBOL_GPL(statistic_define_history);
+EXPORT_SYMBOL_GPL(statistic_start);
+EXPORT_SYMBOL_GPL(statistic_stop);
+EXPORT_SYMBOL_GPL(statistic_reset);
diff -Nurp e/MAINTAINERS f/MAINTAINERS
--- e/MAINTAINERS	2005-12-14 12:51:52.000000000 +0100
+++ f/MAINTAINERS	2005-12-14 14:22:55.000000000 +0100
@@ -2464,6 +2464,13 @@ STARMODE RADIO IP (STRIP) PROTOCOL DRIVE
 W:	http://mosquitonet.Stanford.EDU/strip.html
 S:	Unsupported ?

+STATISTICS INFRASTRUCTURE
+P:	Martin Peschke
+M:	mp3@xxxxxxxxxx
+M:	linux390@xxxxxxxxxx
+W:	http://oss.software.ibm.com/developerworks/opensource/linux390
+S:	Supported
+
 STRADIS MPEG-2 DECODER DRIVER
 P:	Nathan Laredo
 M:	laredo@xxxxxxx
-
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