--- name: "libpmemkv_config" section: "3" platform: "linux" package: "libpmemkv-dev" version: "1.4-1" release: "Debian 11 (Bullseye)" platforms: ["linux"] url: "https://new.carta.tech/libpmemkv_config" --- # libpmemkv\_config(3) Configuration API for libpmemkv ## NAME **pmemkv\_config** - Configuration API for libpmemkv ## SYNOPSIS - ``` #include 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)](/libpmemkv/7.md). For description of pmemkv core API see [**libpmemkv**(3)](/libpmemkv/3.md). ## DESCRIPTION pmemkv database is configured using pmemkv\_config structure. It stores mappings of keys (null-terminated strings) to values. A value can be: - • **uint64\_t** - • **int64\_t** - • **c-style string** - • **binary data** - • **pointer to an object** (with accompanying deleter function) 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)](/libpmemkv/7.md) 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)](/libpmemkv/7.md)). - **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: - • **PMEMKV\_STATUS\_OK** – no error - • **PMEMKV\_STATUS\_UNKNOWN\_ERROR** – unknown error - • **PMEMKV\_STATUS\_NOT\_FOUND** – record (or config item) not found - • **PMEMKV\_STATUS\_CONFIG\_PARSING\_ERROR** – parsing data to config failed - • **PMEMKV\_STATUS\_CONFIG\_TYPE\_ERROR** – config item has different type than expected ## 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 #include #include #include #include #include #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 #include #include #include #include #include #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/7.md), [**libpmemkv**(3)](/libpmemkv/3.md) , [**libpmemkv\_json\_config**(3)](/libpmemkv_json_config/3.md) and **\**