pmemkv man page

pmemkv_config

NAME
SYNOPSIS
DESCRIPTION
ERRORS
EXAMPLE
SEE ALSO

NAME

pmemkv_config - Configuration API for libpmemkv

SYNOPSIS

#include <libpmemkv.h>

pmemkv_config *pmemkv_config_new(void);
void pmemkv_config_delete(pmemkv_config *config);

int pmemkv_config_put_size(pmemkv_config *config, uint64_t value);
int pmemkv_config_put_path(pmemkv_config *config, const char *value);
int pmemkv_config_put_force_create(pmemkv_config *config, bool value);
int pmemkv_config_put_comparator(pmemkv_config *config, pmemkv_comparator *comparator);
int pmemkv_config_put_oid(pmemkv_config *config, PMEMoid *oid);

int pmemkv_config_put_data(pmemkv_config *config, const char *key, const void *value,
			size_t value_size);
int pmemkv_config_put_object(pmemkv_config *config, const char *key, void *value,
			void (*deleter)(void *));
int pmemkv_config_put_object_cb(pmemkv_config *config, const char *key, void *value,
				void *(*getter)(void *), void (*deleter)(void *));
int pmemkv_config_put_uint64(pmemkv_config *config, const char *key, uint64_t value);
int pmemkv_config_put_int64(pmemkv_config *config, const char *key, int64_t value);
int pmemkv_config_put_string(pmemkv_config *config, const char *key, const char *value);

int pmemkv_config_get_data(pmemkv_config *config, const char *key, const void **value,
			size_t *value_size);
int pmemkv_config_get_object(pmemkv_config *config, const char *key, void **value);
int pmemkv_config_get_uint64(pmemkv_config *config, const char *key, uint64_t *value);
int pmemkv_config_get_int64(pmemkv_config *config, const char *key, int64_t *value);
int pmemkv_config_get_string(pmemkv_config *config, const char *key, const char **value);

pmemkv_comparator *pmemkv_comparator_new(pmemkv_compare_function *fn, const char *name,
					 void *arg);
void pmemkv_comparator_delete(pmemkv_comparator *comparator);

For general description of pmemkv and available engines see libpmemkv(7). For description of pmemkv core API see libpmemkv(3).

DESCRIPTION

pmemkv database is configured using pmemkv_config structure. It stores mappings of keys (null-terminated strings) to values. A value can be:

It also delivers methods to store and read configuration items provided by a user. Once the configuration object is set (with all required parameters), it can be passed to pmemkv_open() method.

List of options which are required by pmemkv database is specific to an engine. Every engine has documented all supported config parameters (please see libpmemkv(7) for details).

pmemkv_config *pmemkv_config_new(void);
Creates an instance of configuration for pmemkv database.

On failure, NULL is returned.

void pmemkv_config_delete(pmemkv_config *config);
Deletes pmemkv_config. Should be called ONLY for configs which were not passed to pmemkv_open (as this function moves ownership of the config to the database).
int pmemkv_config_put_size(pmemkv_config *config, uint64_t value);

Puts value to a config at key size. This function provides type safety for size parameter.

int pmemkv_config_put_path(pmemkv_config *config, const char *value);

Puts value to a config at key path. This function provides type safety for path parameter.

int pmemkv_config_put_force_create(pmemkv_config Wconfig, bool value);

Puts force_create parameter to a config. In engines which supports this parameter, if false, pmemkv opens the file specified by path, otherwise it creates it. False by default.

int pmemkv_config_put_comparator(pmemkv_config *config, pmemkv_comparator *comparator);

Puts comparator object to a config. To create an instance of pmemkv_comparator object, pmemkv_comparator_new() function shoud be used.

int pmemkv_config_put_oid(pmemkv_config *config, PMEMoid *oid);

Puts PMEMoid object to a config (for details see libpmemkv(7)).

int pmemkv_config_put_uint64(pmemkv_config *config, const char *key, uint64_t value);

Puts uint64_t value value to pmemkv_config at key key.

int pmemkv_config_put_int64(pmemkv_config *config, const char *key, int64_t value);

Puts int64_t value value to pmemkv_config at key key.

int pmemkv_config_put_string(pmemkv_config *config, const char *key, const char *value);

Puts null-terminated string to pmemkv_config. The string is copied to the config.

int pmemkv_config_put_data(pmemkv_config *config, const char *key, const void *value, size_t value_size);

Puts copy of binary data pointed by value to pmemkv_config. value_size specifies size of the data.

int pmemkv_config_put_object(pmemkv_config *config, const char *key, void *value, void (*deleter)(void *));

Puts value to pmemkv_config. value can point to arbitrary object. deleter parameter specifies function which will be called for value when the config is destroyed (using pmemkv_config_delete).

int pmemkv_config_put_object_cb(pmemkv_config *config, const char *key, void *value, void *(*getter)(void *), void (*deleter)(void *));

Extended version of pmemkv_config_put_object. It accepts one additional argument - a getter callback. This callback interprets the custom object (value) and returns a pointer which is expected by pmemkv.

Calling pmemkv_config_put_object_cb with getter implemented as:

void *getter(void *arg) { return arg; }

is equivalent to calling pmemkv_config_put_object.

int pmemkv_config_get_uint64(pmemkv_config *config, const char *key, uint64_t *value);

Gets value of a config item with key key. Value is copied to variable pointed by value.

int pmemkv_config_get_int64(pmemkv_config *config, const char *key, int64_t *value);

Gets value of a config item with key key. Value is copied to variable pointed by value.

int pmemkv_config_get_string(pmemkv_config *config, const char *key, const char **value);

Gets pointer to a null-terminated string. The string is not copied. After successful call value points to string stored in pmemkv_config.

int pmemkv_config_get_data(pmemkv_config *config, const char *key, const void **value, size_t *value_size);

Gets pointer to binary data. Data is not copied. After successful call *value points to data stored in pmemkv_config and value_size holds size of the data.

int pmemkv_config_get_object(pmemkv_config *config, const char *key, const void **value);

Gets pointer to an object. After successful call, *value points to the object.

Config items stored in pmemkv_config, which were put using a specific function can be obtained only using corresponding pmemkv_config_get_ function (for example, config items put using pmemkv_config_put_object can only be obtained using pmemkv_config_get_object). Exception from this rule are functions for uint64 and int64. If value put by pmemkv_config_put_int64 is in uint64_t range it can be obtained using pmemkv_config_get_uint64 and vice versa.

pmemkv_comparator *pmemkv_comparator_new(pmemkv_compare_function *fn, const char *name, void *arg);

Creates instance of a comparator object. Accepts comparison function fn, name and arg. In case of persistent engines, name is stored within the engine. Attempt to open a database which was createad with different comparator of different name will fail with PMEMKV_STATUS_COMPARATOR_MISMATCH. arg` is saved in the comparator and passed to a comparison function on each invocation.

Neither fn nor name can be NULL.

fn should perform a three-way comparison. Return values:

  • negative value if the first key is less than the second one
  • zero if both keys are the same
  • positive value if the first key is greater than the second one

The comparison function should be thread safe - it can be called from multiple threads.

On failure, NULL is returned.

void pmemkv_comparator_delete(pmemkv_comparator *comparator);

Removes the comparator object. Should be called ONLY for comparators which were not put to config (as config takes ownership of the comparator).

To set a comparator for the database use pmemkv_config_put_object:

pmemkv_comparator *cmp = pmemkv_comparator_new(&compare_fn, "my_comparator", NULL);

pmemkv_config_put_object(cfg, "comparator", cmp, (void (*)(void *)) & pmemkv_comparator_delete);

ERRORS

Each function, except for pmemkv_config_new() and pmemkv_config_delete(), returns status. Possible return values are:

EXAMPLE

The following examples are taken from examples/pmemkv_config_c directory.

BASIC EXAMPLE

Usage of basic config functions to set parameters based on their functionalities, e.g. pmemkv_config_put_path() or pmemkv_config_put_size().

#include <assert.h>
#include <libpmemkv.h>
#include <libpmemobj/pool_base.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define ASSERT(expr)                                                                     \
	do {                                                                             \
		if (!(expr))                                                             \
			puts(pmemkv_errormsg());                                         \
		assert(expr);                                                            \
	} while (0)

static const uint64_t SIZE = 1024UL * 1024UL * 1024UL;

int key_length_compare(const char *key1, size_t keybytes1, const char *key2,
		       size_t keybytes2, void *arg)
{
	if (keybytes2 < keybytes1)
		return -1;
	else if (keybytes2 > keybytes1)
		return 1;
	else
		return 0;
}

int main(int argc, char *argv[])
{
	if (argc < 2) {
		fprintf(stderr, "Usage: %s file\n", argv[0]);
		exit(1);
	}

	/* Create config */
	pmemkv_config *config = pmemkv_config_new();
	ASSERT(config != NULL);

	/* Add path parameter to config. Meaning of this is dependent on chosen engine.
	 *  E.g. if config is used with cmap engine,
	 *  it is a path to a database file or to a poolset file. However for
	 *  vcmap it is a path to an existing directory */
	int status = pmemkv_config_put_path(config, argv[1]);
	ASSERT(status == PMEMKV_STATUS_OK);

	/* Specifies size of the database */
	status = pmemkv_config_put_size(config, SIZE);
	ASSERT(status == PMEMKV_STATUS_OK);

	/* Specifies value of force create flag */
	status = pmemkv_config_put_force_create(config, true);
	ASSERT(status == PMEMKV_STATUS_OK);

	/* Specifies comparator used by the engine */
	pmemkv_comparator *cmp =
		pmemkv_comparator_new(&key_length_compare, "key_length_compare", NULL);
	ASSERT(cmp != NULL);
	status = pmemkv_config_put_comparator(config, cmp);
	ASSERT(status == PMEMKV_STATUS_OK);

	/* Adds pointer to oid (for details see libpmemkv(7)) to the config */
	PMEMoid oid;
	status = pmemkv_config_put_oid(config, &oid);
	ASSERT(status == PMEMKV_STATUS_OK);

	pmemkv_config_delete(config);

	return 0;
}

TYPE BASED CONFIGURATION EXAMPLE

Usage of config functions to set and get data based on their data type, e.g. pmemkv_config_put_int64() or pmemkv_config_put_object().

#include <assert.h>
#include <libpmemkv.h>
#include <libpmemkv_json_config.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define ASSERT(expr)                                                                     \
	do {                                                                             \
		if (!(expr))                                                             \
			puts(pmemkv_errormsg());                                         \
		assert(expr);                                                            \
	} while (0)

/* deleter for int pointer */
void free_int_ptr(void *ptr)
{
	free(ptr);
}

int main()
{
	pmemkv_config *config = pmemkv_config_new();
	ASSERT(config != NULL);

	/* Put int64_t value */
	int status = pmemkv_config_put_int64(config, "size", 1073741824);
	ASSERT(status == PMEMKV_STATUS_OK);

	char buffer[] = "ABC";

	/* Put binary data stored in buffer */
	status = pmemkv_config_put_data(config, "binary", buffer, 3);
	ASSERT(status == PMEMKV_STATUS_OK);

	const void *data;
	size_t data_size;

	/* Get pointer to binary data stored in config */
	status = pmemkv_config_get_data(config, "binary", &data, &data_size);
	ASSERT(status == PMEMKV_STATUS_OK);
	ASSERT(data_size == 3);
	ASSERT(((const char *)data)[0] == 'A');

	int *int_ptr = malloc(sizeof(int));
	ASSERT(int_ptr != NULL);
	*int_ptr = 10;

	/* Put pointer to dynamically allocated object, free_int_ptr is called on
	 * pmemkv_config_delete */
	status = pmemkv_config_put_object(config, "int_ptr", int_ptr, &free_int_ptr);
	ASSERT(status == PMEMKV_STATUS_OK);

	int *get_int_ptr;

	/* Get pointer to object stored in config */
	status = pmemkv_config_get_object(config, "int_ptr", (void **)&get_int_ptr);
	ASSERT(status == PMEMKV_STATUS_OK);
	ASSERT(*get_int_ptr == 10);

	pmemkv_config_delete(config);

	pmemkv_config *config_from_json = pmemkv_config_new();
	ASSERT(config_from_json != NULL);

	/* Parse JSON and put all items found into config_from_json */
	status = pmemkv_config_from_json(config_from_json, "{\"path\":\"/dev/shm\",\
		 \"size\":1073741824,\
		 \"subconfig\":{\
			\"size\":1073741824\
			}\
		}");
	ASSERT(status == PMEMKV_STATUS_OK);

	const char *path;
	status = pmemkv_config_get_string(config_from_json, "path", &path);
	ASSERT(status == PMEMKV_STATUS_OK);
	ASSERT(strcmp(path, "/dev/shm") == 0);

	pmemkv_config *subconfig;

	/* Get pointer to nested configuration "subconfig" */
	status = pmemkv_config_get_object(config_from_json, "subconfig",
					  (void **)&subconfig);
	ASSERT(status == PMEMKV_STATUS_OK);

	size_t sub_size;
	status = pmemkv_config_get_uint64(subconfig, "size", &sub_size);
	ASSERT(status == PMEMKV_STATUS_OK);
	ASSERT(sub_size == 1073741824);

	pmemkv_config_delete(config_from_json);

	return 0;
}

SEE ALSO

libpmemkv(7), libpmemkv(3) , libpmemkv_json_config(3) and https://pmem.io