lvm2/libdm/libdevmapper.h

/*
 * Copyright (C) 2001-2004 Sistina Software, Inc. All rights reserved.
 * Copyright (C) 2004-2017 Red Hat, Inc. All rights reserved.
 * Copyright (C) 2006 Rackable Systems All rights reserved.
 *
 * This file is part of the device-mapper userspace tools.
 *
 * This copyrighted material is made available to anyone wishing to use,
 * modify, copy, or redistribute it subject to the terms and conditions
 * of the GNU Lesser General Public License v.2.1.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#ifndef LIB_DEVICE_MAPPER_H
#define LIB_DEVICE_MAPPER_H

#include <inttypes.h>
#include <stdarg.h>
#include <sys/types.h>
#include <sys/stat.h>

#ifdef __linux__
#  include <linux/types.h>
#endif

#include <limits.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>

#ifndef __GNUC__
# define __typeof__ typeof
#endif

/* Macros to make string defines */
#define DM_TO_STRING_EXP(A) #A
#define DM_TO_STRING(A) DM_TO_STRING_EXP(A)

#define DM_ARRAY_SIZE(a) (sizeof(a) / sizeof((a)[0]))

#ifdef __cplusplus
extern "C" {
#endif

/*****************************************************************
 * The first section of this file provides direct access to the
 * individual device-mapper ioctls.  Since it is quite laborious to
 * build the ioctl arguments for the device-mapper, people are
 * encouraged to use this library.
 ****************************************************************/

/*
 * The library user may wish to register their own
 * logging function.  By default errors go to stderr.
 * Use dm_log_with_errno_init(NULL) to restore the default log fn.
 * Error messages may have a non-zero errno.
 * Debug messages may have a non-zero class.
 * Aborts on internal error when env DM_ABORT_ON_INTERNAL_ERRORS is 1
 */

typedef void (*dm_log_with_errno_fn) (int level, const char *file, int line,
				      int dm_errno_or_class, const char *f, ...)
    __attribute__ ((format(printf, 5, 6)));

void dm_log_with_errno_init(dm_log_with_errno_fn fn);
void dm_log_init_verbose(int level);

/*
 * Original version of this function.
 * dm_errno is set to 0.
 *
 * Deprecated: Use the _with_errno_ versions above instead.
 */
typedef void (*dm_log_fn) (int level, const char *file, int line,
			   const char *f, ...)
    __attribute__ ((format(printf, 4, 5)));

void dm_log_init(dm_log_fn fn);
/*
 * For backward-compatibility, indicate that dm_log_init() was used
 * to set a non-default value of dm_log().
 */
int dm_log_is_non_default(void);

/*
 * Number of devices currently in suspended state (via the library).
 */
int dm_get_suspended_counter(void);

enum {
	DM_DEVICE_CREATE,
	DM_DEVICE_RELOAD,
	DM_DEVICE_REMOVE,
	DM_DEVICE_REMOVE_ALL,

	DM_DEVICE_SUSPEND,
	DM_DEVICE_RESUME,

	DM_DEVICE_INFO,
	DM_DEVICE_DEPS,
	DM_DEVICE_RENAME,

	DM_DEVICE_VERSION,

	DM_DEVICE_STATUS,
	DM_DEVICE_TABLE,
	DM_DEVICE_WAITEVENT,

	DM_DEVICE_LIST,

	DM_DEVICE_CLEAR,

	DM_DEVICE_MKNODES,

	DM_DEVICE_LIST_VERSIONS,
	
	DM_DEVICE_TARGET_MSG,

	DM_DEVICE_SET_GEOMETRY
};

/*
 * You will need to build a struct dm_task for
 * each ioctl command you want to execute.
 */

struct dm_pool;
struct dm_task;
struct dm_timestamp;

struct dm_task *dm_task_create(int type);
void dm_task_destroy(struct dm_task *dmt);

int dm_task_set_name(struct dm_task *dmt, const char *name);
int dm_task_set_uuid(struct dm_task *dmt, const char *uuid);

/*
 * Retrieve attributes after an info.
 */
struct dm_info {
	int exists;
	int suspended;
	int live_table;
	int inactive_table;
	int32_t open_count;
	uint32_t event_nr;
	uint32_t major;
	uint32_t minor;		/* minor device number */
	int read_only;		/* 0:read-write; 1:read-only */

	int32_t target_count;

	int deferred_remove;
	int internal_suspend;
};

struct dm_deps {
	uint32_t count;
	uint32_t filler;
	uint64_t device[0];
};

struct dm_names {
	uint64_t dev;
	uint32_t next;		/* Offset to next struct from start of this struct */
	char name[0];
};

struct dm_versions {
	uint32_t next;		/* Offset to next struct from start of this struct */
	uint32_t version[3];

	char name[0];
};

int dm_get_library_version(char *version, size_t size);
int dm_task_get_driver_version(struct dm_task *dmt, char *version, size_t size);
int dm_task_get_info(struct dm_task *dmt, struct dm_info *dmi);

/*
 * This function returns dm device's UUID based on the value
 * of the mangling mode set during preceding dm_task_run call:
 *   - unmangled UUID for DM_STRING_MANGLING_{AUTO, HEX},
 *   - UUID without any changes for DM_STRING_MANGLING_NONE.
 *
 * To get mangled or unmangled form of the UUID directly, use
 * dm_task_get_uuid_mangled or dm_task_get_uuid_unmangled function.
 */
const char *dm_task_get_uuid(const struct dm_task *dmt);

struct dm_deps *dm_task_get_deps(struct dm_task *dmt);
struct dm_versions *dm_task_get_versions(struct dm_task *dmt);
const char *dm_task_get_message_response(struct dm_task *dmt);

/*
 * These functions return device-mapper names based on the value
 * of the mangling mode set during preceding dm_task_run call:
 *   - unmangled name for DM_STRING_MANGLING_{AUTO, HEX},
 *   - name without any changes for DM_STRING_MANGLING_NONE.
 *
 * To get mangled or unmangled form of the name directly, use
 * dm_task_get_name_mangled or dm_task_get_name_unmangled function.
 */
const char *dm_task_get_name(const struct dm_task *dmt);
struct dm_names *dm_task_get_names(struct dm_task *dmt);

int dm_task_set_ro(struct dm_task *dmt);
int dm_task_set_newname(struct dm_task *dmt, const char *newname);
int dm_task_set_newuuid(struct dm_task *dmt, const char *newuuid);
int dm_task_set_minor(struct dm_task *dmt, int minor);
int dm_task_set_major(struct dm_task *dmt, int major);
int dm_task_set_major_minor(struct dm_task *dmt, int major, int minor, int allow_default_major_fallback);
int dm_task_set_uid(struct dm_task *dmt, uid_t uid);
int dm_task_set_gid(struct dm_task *dmt, gid_t gid);
int dm_task_set_mode(struct dm_task *dmt, mode_t mode);
/* See also description for DM_UDEV_DISABLE_LIBRARY_FALLBACK flag! */
int dm_task_set_cookie(struct dm_task *dmt, uint32_t *cookie, uint16_t flags);
int dm_task_set_event_nr(struct dm_task *dmt, uint32_t event_nr);
int dm_task_set_geometry(struct dm_task *dmt, const char *cylinders, const char *heads, const char *sectors, const char *start);
int dm_task_set_message(struct dm_task *dmt, const char *message);
int dm_task_set_sector(struct dm_task *dmt, uint64_t sector);
int dm_task_no_flush(struct dm_task *dmt);
int dm_task_no_open_count(struct dm_task *dmt);
int dm_task_skip_lockfs(struct dm_task *dmt);
int dm_task_query_inactive_table(struct dm_task *dmt);
int dm_task_suppress_identical_reload(struct dm_task *dmt);
int dm_task_secure_data(struct dm_task *dmt);
int dm_task_retry_remove(struct dm_task *dmt);
int dm_task_deferred_remove(struct dm_task *dmt);

/*
 * Record timestamp immediately after the ioctl returns.
 */
int dm_task_set_record_timestamp(struct dm_task *dmt);
struct dm_timestamp *dm_task_get_ioctl_timestamp(struct dm_task *dmt);

/*
 * Enable checks for common mistakes such as issuing ioctls in an unsafe order.
 */
int dm_task_enable_checks(struct dm_task *dmt);

typedef enum {
	DM_ADD_NODE_ON_RESUME, /* add /dev/mapper node with dmsetup resume */
	DM_ADD_NODE_ON_CREATE  /* add /dev/mapper node with dmsetup create */
} dm_add_node_t;
int dm_task_set_add_node(struct dm_task *dmt, dm_add_node_t add_node);

/*
 * Control read_ahead.
 */
#define DM_READ_AHEAD_AUTO UINT32_MAX	/* Use kernel default readahead */
#define DM_READ_AHEAD_NONE 0		/* Disable readahead */

#define DM_READ_AHEAD_MINIMUM_FLAG	0x1	/* Value supplied is minimum */

/*
 * Read ahead is set with DM_DEVICE_CREATE with a table or DM_DEVICE_RESUME.
 */
int dm_task_set_read_ahead(struct dm_task *dmt, uint32_t read_ahead,
			   uint32_t read_ahead_flags);
uint32_t dm_task_get_read_ahead(const struct dm_task *dmt,
				uint32_t *read_ahead);

/*
 * Use these to prepare for a create or reload.
 */
int dm_task_add_target(struct dm_task *dmt,
		       uint64_t start,
		       uint64_t size, const char *ttype, const char *params);

/*
 * Format major/minor numbers correctly for input to driver.
 */
#define DM_FORMAT_DEV_BUFSIZE	13	/* Minimum bufsize to handle worst case. */
int dm_format_dev(char *buf, int bufsize, uint32_t dev_major, uint32_t dev_minor);

/* Use this to retrive target information returned from a STATUS call */
void *dm_get_next_target(struct dm_task *dmt,
			 void *next, uint64_t *start, uint64_t *length,
			 char **target_type, char **params);

/*
 * Following dm_get_status_* functions will allocate approriate status structure
 * from passed mempool together with the necessary character arrays.
 * Destroying the mempool will release all asociated allocation.
 */

/* Parse params from STATUS call for mirror target */
typedef enum {
	DM_STATUS_MIRROR_ALIVE	      = 'A',/* No failures */
	DM_STATUS_MIRROR_FLUSH_FAILED = 'F',/* Mirror out-of-sync */
	DM_STATUS_MIRROR_WRITE_FAILED = 'D',/* Mirror out-of-sync */
	DM_STATUS_MIRROR_SYNC_FAILED  = 'S',/* Mirror out-of-sync */
	DM_STATUS_MIRROR_READ_FAILED  = 'R',/* Mirror data unaffected */
	DM_STATUS_MIRROR_UNCLASSIFIED = 'U' /* Bug */
} dm_status_mirror_health_t;

struct dm_status_mirror {
	uint64_t total_regions;
	uint64_t insync_regions;
	uint32_t dev_count;             /* # of devs[] elements (<= 8) */
	struct {
		dm_status_mirror_health_t health;
		uint32_t major;
		uint32_t minor;
	} *devs;                        /* array with individual legs */
	const char *log_type;           /* core, disk,.... */
	uint32_t log_count;		/* # of logs[] elements */
	struct {
		dm_status_mirror_health_t health;
		uint32_t major;
		uint32_t minor;
	} *logs;			/* array with individual logs */
};

int dm_get_status_mirror(struct dm_pool *mem, const char *params,
			 struct dm_status_mirror **status);

/* Parse params from STATUS call for raid target */
struct dm_status_raid {
	uint64_t reserved;
	uint64_t total_regions;		/* sectors */
	uint64_t insync_regions;	/* sectors */
	uint64_t mismatch_count;
	uint32_t dev_count;
	char *raid_type;
	/* A - alive,  a - alive not in-sync,  D - dead/failed */
	char *dev_health;
	/* idle, frozen, resync, recover, check, repair */
	char *sync_action;
	uint64_t data_offset; /* RAID out-of-place reshaping */
};

int dm_get_status_raid(struct dm_pool *mem, const char *params,
		       struct dm_status_raid **status);

/* Parse params from STATUS call for cache target */
struct dm_status_cache {
	uint64_t version;  /* zero for now */

	uint32_t metadata_block_size;   /* in 512B sectors */
	uint32_t block_size;            /* AKA 'chunk_size' */

	uint64_t metadata_used_blocks;
	uint64_t metadata_total_blocks;

	uint64_t used_blocks;
	uint64_t dirty_blocks;
	uint64_t total_blocks;

	uint64_t read_hits;
	uint64_t read_misses;
	uint64_t write_hits;
	uint64_t write_misses;

	uint64_t demotions;
	uint64_t promotions;

	uint64_t feature_flags;		/* DM_CACHE_FEATURE_? */

	int core_argc;
	char **core_argv;

	char *policy_name;
	int policy_argc;
	char **policy_argv;

	unsigned error : 1;		/* detected error (switches to fail soon) */
	unsigned fail : 1;		/* all I/O fails */
	unsigned needs_check : 1;	/* metadata needs check */
	unsigned read_only : 1;		/* metadata may not be changed */
	uint32_t reserved : 28;
};

int dm_get_status_cache(struct dm_pool *mem, const char *params,
			struct dm_status_cache **status);

/*
 * Parse params from STATUS call for snapshot target
 *
 * Snapshot target's format:
 * <= 1.7.0: <used_sectors>/<total_sectors>
 * >= 1.8.0: <used_sectors>/<total_sectors> <metadata_sectors>
 */
struct dm_status_snapshot {
	uint64_t used_sectors;          /* in 512b units */
	uint64_t total_sectors;
	uint64_t metadata_sectors;
	unsigned has_metadata_sectors : 1; /* set when metadata_sectors is present */
	unsigned invalid : 1;		/* set when snapshot is invalidated */
	unsigned merge_failed : 1;	/* set when snapshot merge failed */
	unsigned overflow : 1;		/* set when snapshot overflows */
};

int dm_get_status_snapshot(struct dm_pool *mem, const char *params,
			   struct dm_status_snapshot **status);

/* Parse params from STATUS call for thin_pool target */
typedef enum {
	DM_THIN_DISCARDS_IGNORE,
	DM_THIN_DISCARDS_NO_PASSDOWN,
	DM_THIN_DISCARDS_PASSDOWN
} dm_thin_discards_t;

struct dm_status_thin_pool {
	uint64_t transaction_id;
	uint64_t used_metadata_blocks;
	uint64_t total_metadata_blocks;
	uint64_t used_data_blocks;
	uint64_t total_data_blocks;
	uint64_t held_metadata_root;
	uint32_t read_only;		/* metadata may not be changed */
	dm_thin_discards_t discards;
	uint32_t fail : 1;		/* all I/O fails */
	uint32_t error_if_no_space : 1;	/* otherwise queue_if_no_space */
	uint32_t out_of_data_space : 1;	/* metadata may be changed, but data may not be allocated (no rw) */
	uint32_t needs_check : 1;	/* metadata needs check */
	uint32_t error : 1;		/* detected error (switches to fail soon) */
	uint32_t reserved : 27;
};

int dm_get_status_thin_pool(struct dm_pool *mem, const char *params,
			    struct dm_status_thin_pool **status);

/* Parse params from STATUS call for thin target */
struct dm_status_thin {
	uint64_t mapped_sectors;
	uint64_t highest_mapped_sector;
	uint32_t fail : 1;              /* Thin volume fails I/O */
	uint32_t reserved : 31;
};

int dm_get_status_thin(struct dm_pool *mem, const char *params,
		       struct dm_status_thin **status);

/*
 * device-mapper statistics support
 */

/*
 * Statistics handle.
 *
 * Operations on dm_stats objects include managing statistics regions
 * and obtaining and manipulating current counter values from the
 * kernel. Methods are provided to return baisc count values and to
 * derive time-based metrics when a suitable interval estimate is
 * provided.
 *
 * Internally the dm_stats handle contains a pointer to a table of one
 * or more dm_stats_region objects representing the regions registered
 * with the dm_stats_create_region() method. These in turn point to a
 * table of one or more dm_stats_counters objects containing the
 * counter sets for each defined area within the region:
 *
 * dm_stats->dm_stats_region[nr_regions]->dm_stats_counters[nr_areas]
 *
 * This structure is private to the library and may change in future
 * versions: all users should make use of the public interface and treat
 * the dm_stats type as an opaque handle.
 *
 * Regions and counter sets are stored in order of increasing region_id.
 * Depending on region specifications and the sequence of create and
 * delete operations this may not correspond to increasing sector
 * number: users of the library should not assume that this is the case
 * unless region creation is deliberately managed to ensure this (by
 * always creating regions in strict order of ascending sector address).
 *
 * Regions may also overlap so the same sector range may be included in
 * more than one region or area: applications should be prepared to deal
 * with this or manage regions such that it does not occur.
 */
struct dm_stats;

/*
 * Histogram handle.
 *
 * A histogram object represents the latency histogram values and bin
 * boundaries of the histogram associated with a particular area.
 *
 * Operations on the handle allow the number of bins, bin boundaries,
 * counts and relative proportions to be obtained as well as the
 * conversion of a histogram or its bounds to a compact string
 * representation.
 */
struct dm_histogram;

/*
 * Allocate a dm_stats handle to use for subsequent device-mapper
 * statistics operations. A program_id may be specified and will be
 * used by default for subsequent operations on this handle.
 *
 * If program_id is NULL or the empty string a program_id will be
 * automatically set to the value contained in /proc/self/comm.
 */
struct dm_stats *dm_stats_create(const char *program_id);

/*
 * Bind a dm_stats handle to the specified device major and minor
 * values. Any previous binding is cleared and any preexisting counter
 * data contained in the handle is released.
 */
int dm_stats_bind_devno(struct dm_stats *dms, int major, int minor);

/*
 * Bind a dm_stats handle to the specified device name.
 * Any previous binding is cleared and any preexisting counter
 * data contained in the handle is released.
 */
int dm_stats_bind_name(struct dm_stats *dms, const char *name);

/*
 * Bind a dm_stats handle to the specified device UUID.
 * Any previous binding is cleared and any preexisting counter
 * data contained in the handle is released.
 */
int dm_stats_bind_uuid(struct dm_stats *dms, const char *uuid);

/*
 * Bind a dm_stats handle to the device backing the file referenced
 * by the specified file descriptor.
 *
 * File descriptor fd must reference a regular file, open for reading,
 * in a local file system, backed by a device-mapper device, that
 * supports the FIEMAP ioctl, and that returns data describing the
 * physical location of extents.
 */
int dm_stats_bind_from_fd(struct dm_stats *dms, int fd);
/*
 * Test whether the running kernel supports the precise_timestamps
 * feature. Presence of this feature also implies histogram support.
 * The library will check this call internally and fails any attempt
 * to use nanosecond counters or histograms on kernels that fail to
 * meet this check.
 */
int dm_message_supports_precise_timestamps(void);

/*
 * Precise timetamps and histogram support.
 * 
 * Test for the presence of precise_timestamps and histogram support.
 */
int dm_stats_driver_supports_precise(void);
int dm_stats_driver_supports_histogram(void);

/*
 * Returns 1 if the specified region has the precise_timestamps feature
 * enabled (i.e. produces nanosecond-precision counter values) or 0 for
 * a region using the default milisecond precision.
 */
int dm_stats_get_region_precise_timestamps(const struct dm_stats *dms,
					   uint64_t region_id);

/*
 * Returns 1 if the region at the current cursor location has the
 * precise_timestamps feature enabled (i.e. produces
 * nanosecond-precision counter values) or 0 for a region using the
 * default milisecond precision.
 */
int dm_stats_get_current_region_precise_timestamps(const struct dm_stats *dms);

#define DM_STATS_ALL_PROGRAMS ""
/*
 * Parse the response from a @stats_list message. dm_stats_list will
 * allocate the necessary dm_stats and dm_stats region structures from
 * the embedded dm_pool. No counter data will be obtained (the counters
 * members of dm_stats_region objects are set to NULL).
 *
 * A program_id may optionally be supplied; if the argument is non-NULL
 * only regions with a matching program_id value will be considered. If
 * the argument is NULL then the default program_id associated with the
 * dm_stats handle will be used. Passing the special value
 * DM_STATS_ALL_PROGRAMS will cause all regions to be queried
 * regardless of region program_id.
 */
int dm_stats_list(struct dm_stats *dms, const char *program_id);

#define DM_STATS_REGIONS_ALL UINT64_MAX
/*
 * Populate a dm_stats object with statistics for one or more regions of
 * the specified device.
 *
 * A program_id may optionally be supplied; if the argument is non-NULL
 * only regions with a matching program_id value will be considered. If
 * the argument is NULL then the default program_id associated with the
 * dm_stats handle will be used. Passing the special value
 * DM_STATS_ALL_PROGRAMS will cause all regions to be queried
 * regardless of region program_id.
 *
 * Passing the special value DM_STATS_REGIONS_ALL as the region_id
 * argument will attempt to retrieve all regions selected by the
 * program_id argument.
 *
 * If region_id is used to request a single region_id to be populated
 * the program_id is ignored.
 */
int dm_stats_populate(struct dm_stats *dms, const char *program_id,
		      uint64_t region_id);

/*
 * Create a new statistics region on the device bound to dms.
 *
 * start and len specify the region start and length in 512b sectors.
 * Passing zero for both start and len will create a region spanning
 * the entire device.
 *
 * Step determines how to subdivide the region into discrete counter
 * sets: a positive value specifies the size of areas into which the
 * region should be split while a negative value will split the region
 * into a number of areas equal to the absolute value of step:
 *
 * - a region with one area spanning the entire device:
 *
 *   dm_stats_create_region(dms, 0, 0, -1, p, a);
 *
 * - a region with areas of 1MiB:
 *
 *   dm_stats_create_region(dms, 0, 0, 1 << 11, p, a);
 *
 * - one 1MiB region starting at 1024 sectors with two areas:
 *
 *   dm_stats_create_region(dms, 1024, 1 << 11, -2, p, a);
 *
 * If precise is non-zero attempt to create a region with nanosecond
 * precision counters using the kernel precise_timestamps feature.
 *
 * precise - A flag to request nanosecond precision counters
 * to be used for this region.
 *
 * histogram_bounds - specify the boundaries of a latency histogram to
 * be tracked for the region. The values are expressed as an array of
 * uint64_t terminated with a zero. Values must be in order of ascending
 * magnitude and specify the upper bounds of successive histogram bins
 * in nanoseconds (with an implicit lower bound of zero on the first bin
 * and an implicit upper bound of infinity on the final bin). For
 * example:
 *
 *   uint64_t bounds_ary[] = { 1000, 2000, 3000, 0 };
 *
 * Specifies a histogram with four bins: 0-1000ns, 1000-2000ns,
 * 2000-3000ns and >3000ns.
 *
 * The smallest latency value that can be tracked for a region not using
 * precise_timestamps is 1ms: attempting to create a region with
 * histogram boundaries < 1ms will cause the precise_timestamps feature
 * to be enabled for that region automatically if it was not requested
 * explicitly.
 *
 * program_id is an optional string argument that identifies the
 * program creating the region. If program_id is NULL or the empty
 * string the default program_id stored in the handle will be used.
 *
 * user_data is an optional string argument that is added to the
 * content of the aux_data field stored with the statistics region by
 * the kernel.
 *
 * The library may also use this space internally, for example, to
 * store a group descriptor or other metadata: in this case the
 * library will strip any internal data fields from the value before
 * it is returned via a call to dm_stats_get_region_aux_data().
 *
 * The user data stored is not accessed by the library or kernel and
 * may be used to store an arbitrary data word (embedded whitespace is
 * not permitted).
 *
 * An application using both the library and direct access to the
 * @stats_list device-mapper message may see the internal values stored
 * in this field by the library. In such cases any string up to and
 * including the first '#' in the field must be treated as an opaque
 * value and preserved across any external modification of aux_data.
 *
 * The region_id of the newly-created region is returned in *region_id
 * if it is non-NULL.
 */
int dm_stats_create_region(struct dm_stats *dms, uint64_t *region_id,
			   uint64_t start, uint64_t len, int64_t step,
			   int precise, struct dm_histogram *bounds,
			   const char *program_id, const char *user_data);

/*
 * Delete the specified statistics region. This will also mark the
 * region as not-present and discard any existing statistics data.
 */
int dm_stats_delete_region(struct dm_stats *dms, uint64_t region_id);

/*
 * Clear the specified statistics region. This requests the kernel to
 * zero all counter values (except in-flight I/O). Note that this
 * operation is not atomic with respect to reads of the counters; any IO
 * events occurring between the last print operation and the clear will
 * be lost. This can be avoided by using the atomic print-and-clear
 * function of the dm_stats_print_region() call or by using the higher
 * level dm_stats_populate() interface.
 */
int dm_stats_clear_region(struct dm_stats *dms, uint64_t region_id);