dm: add statistics support

DM statistics

=============

Device Mapper supports the collection of I/O statistics on user-defined

regions of a DM device.	 If no regions are defined no statistics are

collected so there isn't any performance impact.  Only bio-based DM

devices are currently supported.

Each user-defined region specifies a starting sector, length and step.

Individual statistics will be collected for each step-sized area within

the range specified.

The I/O statistics counters for each step-sized area of a region are

in the same format as /sys/block/*/stat or /proc/diskstats (see:

Documentation/iostats.txt).  But two extra counters (12 and 13) are

provided: total time spent reading and writing in milliseconds.	 All

these counters may be accessed by sending the @stats_print message to

the appropriate DM device via dmsetup.

Each region has a corresponding unique identifier, which we call a

region_id, that is assigned when the region is created.	 The region_id

must be supplied when querying statistics about the region, deleting the

region, etc.  Unique region_ids enable multiple userspace programs to

request and process statistics for the same DM device without stepping

on each other's data.

The creation of DM statistics will allocate memory via kmalloc or

fallback to using vmalloc space.  At most, 1/4 of the overall system

memory may be allocated by DM statistics.  The admin can see how much

memory is used by reading

/sys/module/dm_mod/parameters/stats_current_allocated_bytes

Messages

========

    @stats_create <range> <step> [<program_id> [<aux_data>]]

	Create a new region and return the region_id.

	<range>

	  "-" - whole device

	  "<start_sector>+<length>" - a range of <length> 512-byte sectors

				      starting with <start_sector>.

	<step>

	  "<area_size>" - the range is subdivided into areas each containing

			  <area_size> sectors.

	  "/<number_of_areas>" - the range is subdivided into the specified

				 number of areas.

	<program_id>

	  An optional parameter.  A name that uniquely identifies

	  the userspace owner of the range.  This groups ranges together

	  so that userspace programs can identify the ranges they

	  created and ignore those created by others.

	  The kernel returns this string back in the output of

	  @stats_list message, but it doesn't use it for anything else.

	<aux_data>

	  An optional parameter.  A word that provides auxiliary data

	  that is useful to the client program that created the range.

	  The kernel returns this string back in the output of

	  @stats_list message, but it doesn't use this value for anything.

    @stats_delete <region_id>

	Delete the region with the specified id.

	<region_id>

	  region_id returned from @stats_create

    @stats_clear <region_id>

	Clear all the counters except the in-flight i/o counters.

	<region_id>

	  region_id returned from @stats_create

    @stats_list [<program_id>]

	List all regions registered with @stats_create.

	<program_id>

	  An optional parameter.

	  If this parameter is specified, only matching regions

	  are returned.

	  If it is not specified, all regions are returned.

	Output format:

	  <region_id>: <start_sector>+<length> <step> <program_id> <aux_data>

    @stats_print <region_id> [<starting_line> <number_of_lines>]

	Print counters for each step-sized area of a region.

	<region_id>

	  region_id returned from @stats_create

	<starting_line>

	  The index of the starting line in the output.

	  If omitted, all lines are returned.

	<number_of_lines>

	  The number of lines to include in the output.

	  If omitted, all lines are returned.

	Output format for each step-sized area of a region:

	  <start_sector>+<length> counters

	  The first 11 counters have the same meaning as

	  /sys/block/*/stat or /proc/diskstats.

	  Please refer to Documentation/iostats.txt for details.

	  1. the number of reads completed

	  2. the number of reads merged

	  3. the number of sectors read

	  4. the number of milliseconds spent reading

	  5. the number of writes completed

	  6. the number of writes merged

	  7. the number of sectors written

	  8. the number of milliseconds spent writing

	  9. the number of I/Os currently in progress

	  10. the number of milliseconds spent doing I/Os

	  11. the weighted number of milliseconds spent doing I/Os

	  Additional counters:

	  12. the total time spent reading in milliseconds

	  13. the total time spent writing in milliseconds

    @stats_print_clear <region_id> [<starting_line> <number_of_lines>]

	Atomically print and then clear all the counters except the

	in-flight i/o counters.	 Useful when the client consuming the

	statistics does not want to lose any statistics (those updated

	between printing and clearing).

	<region_id>

	  region_id returned from @stats_create

	<starting_line>

	  The index of the starting line in the output.

	  If omitted, all lines are printed and then cleared.

	<number_of_lines>

	  The number of lines to process.

	  If omitted, all lines are printed and then cleared.

    @stats_set_aux <region_id> <aux_data>

	Store auxiliary data aux_data for the specified region.

	<region_id>

	  region_id returned from @stats_create

	<aux_data>

	  The string that identifies data which is useful to the client

	  program that created the range.  The kernel returns this

	  string back in the output of @stats_list message, but it

	  doesn't use this value for anything.

Examples

========

Subdivide the DM device 'vol' into 100 pieces and start collecting

statistics on them:

  dmsetup message vol 0 @stats_create - /100

Set the auxillary data string to "foo bar baz" (the escape for each

space must also be escaped, otherwise the shell will consume them):

  dmsetup message vol 0 @stats_set_aux 0 foo\\ bar\\ baz

List the statistics:

  dmsetup message vol 0 @stats_list

Print the statistics:

  dmsetup message vol 0 @stats_print 0

Delete the statistics:

  dmsetup message vol 0 @stats_delete 0

#

dm-mod-y	+= dm.o dm-table.o dm-target.o dm-linear.o dm-stripe.o \

		   dm-ioctl.o dm-io.o dm-kcopyd.o dm-sysfs.o

		   dm-ioctl.o dm-io.o dm-kcopyd.o dm-sysfs.o dm-stats.o

dm-multipath-y	+= dm-path-selector.o dm-mpath.o

dm-snapshot-y	+= dm-snap.o dm-exception-store.o dm-snap-transient.o \

		    dm-snap-persistent.o

	return 0;

}

static bool buffer_test_overflow(char *result, unsigned maxlen)

{

	return !maxlen || strlen(result) + 1 >= maxlen;

}

/*

 * Process device-mapper dependent messages.

 * Process device-mapper dependent messages.  Messages prefixed with '@'

 * are processed by the DM core.  All others are delivered to the target.

 * Returns a number <= 1 if message was processed by device mapper.

 * Returns 2 if message should be delivered to the target.

 */

static int message_for_md(struct mapped_device *md, unsigned argc, char **argv,

			  char *result, unsigned maxlen)

{

	return 2;

	int r;

	if (**argv != '@')

		return 2; /* no '@' prefix, deliver to target */

	r = dm_stats_message(md, argc, argv, result, maxlen);

	if (r < 2)

		return r;

	DMERR("Unsupported message sent to DM core: %s", argv[0]);

	return -EINVAL;

}

/*

	if (r == 1) {

		param->flags |= DM_DATA_OUT_FLAG;

		if (buffer_test_overflow(result, maxlen))

		if (dm_message_test_buffer_overflow(result, maxlen))

			param->flags |= DM_BUFFER_FULL_FLAG;

		else

			param->data_size = param->data_start + strlen(result) + 1;

#ifndef DM_STATS_H

#define DM_STATS_H

#include <linux/types.h>

#include <linux/mutex.h>

#include <linux/list.h>

int dm_statistics_init(void);

void dm_statistics_exit(void);

struct dm_stats {

	struct mutex mutex;

	struct list_head list;	/* list of struct dm_stat */

	struct dm_stats_last_position __percpu *last;

	sector_t last_sector;

	unsigned last_rw;

};

struct dm_stats_aux {

	bool merged;

};

void dm_stats_init(struct dm_stats *st);

void dm_stats_cleanup(struct dm_stats *st);

struct mapped_device;

int dm_stats_message(struct mapped_device *md, unsigned argc, char **argv,

		     char *result, unsigned maxlen);

void dm_stats_account_io(struct dm_stats *stats, unsigned long bi_rw,

			 sector_t bi_sector, unsigned bi_sectors, bool end,

			 unsigned long duration, struct dm_stats_aux *aux);

static inline bool dm_stats_used(struct dm_stats *st)

{

	return !list_empty(&st->list);

}

#endif