PMEMCTO_OPEN(3)

NAME

pmemcto_create(), pmemcto_open(), pmemcto_close(), pmemcto_check() – create, open, close and validate close-to-open persistence pool

SYNOPSIS

    #include <libpmemcto.h>
    PMEMctopool *pmemcto_create(const char *path, const char *layout,
            size_t poolsize, mode_t mode);
    PMEMctopool *pmemcto_open(const char *path, const char *layout);
    void pmemcto_close(PMEMctopool *pcp);
    int pmemcto_check(const char *path, const char *layout);

DESCRIPTION

The pmemcto_create() function creates a close-to-open persistence pool with the given total poolsize. The resulting pool is then used with functions like pmemcto_malloc(3) and pmemcto_free(3) to provide the familiar malloc-like programming model for the memory pool. path specifies the name of the memory pool file to be created. layout specifies the application's layout type in the form of a string. The layout name is not interpreted by libpmemcto(7), but may be used as a check when pmemcto_open() is called. The layout name, including the terminating null byte (`\0'), cannot be longer than PMEMCTO_MAX_LAYOUT as defined in <libpmemcto.h>. A NULL layout is equivalent to using an empty string as a layout name. mode specifies the permissions to use when creating the file, as described by creat(2). The memory pool file is fully allocated to the size poolsize using posix_fallocate(3). The caller may choose to take responsibility for creating the memory pool file by creating it before calling pmemcto_create(), and then specifying poolsize as zero. In this case pmemcto_create() will take the pool size from the size of the existing file and will verify that the file appears to be empty by searching for any non-zero data in the pool header at the beginning of the file. The minimum net pool size allowed by the library for a local close-to-open persistence pool is defined in <libpmemcto.h> as PMEMCTO_MIN_POOL.

Depending on the configuration of the system, the available non-volatile memory space may be divided into multiple memory devices. In such case, the maximum size of the pmemcto memory pool could be limited by the capacity of a single memory device. libpmemcto(7) allows building a close-to-open persistence pool spanning multiple memory devices by creation of persistent memory pools consisting of multiple files, where each part of such a pool set may be stored on a different memory device or pmem-aware filesystem.

Creation of all the parts of the pool set can be done with pmemcto_create(); however, the recommended method for creating pool sets is by using the pmempool(1) utility.

When creating a pool set consisting of multiple files, the path argument passed to pmemcto_create() must point to the special set file that defines the pool layout and the location of all the parts of the pool set. The poolsize argument must be 0. The meaning of the layout and mode arguments does not change, except that the same mode is used for creation of all the parts of the pool set.

For more information on pool set format, see poolset(5).

The pmemcto_open() function opens an existing close-to-open persistence memory pool. path must be an existing file containing a pmemcto memory pool as created by pmemcto_create(). If layout is non-NULL, it is compared to the layout name provided to pmemcto_create() when the pool was first created. This can be used to verify that the layout of the pool matches what was expected. The application must have permission to open the file and memory map it with read/write permissions.

The pmemcto_close() function closes the memory pool indicated by pcp and deletes the memory pool handle. The close-to-open memory pool itself lives on in the file that contains it and may be re-opened at a later time using pmemcto_open() as described above. If the pool was not closed gracefully due to abnormal program termination or power failure, the pool is in an inconsistent state causing subsequent pool opening to fail.

The pmemcto_check() function performs a consistency check of the file indicated by path, and returns 1 if the memory pool is found to be consistent. If the pool is found not to be consistent, further use of the file with libpmemcto(7) will result in undefined behavior. The debug version of libpmemcto(7) will provide additional details on inconsistencies when PMEMCTO_LOG_LEVEL is at least 1, as described in the DEBUGGING AND ERROR HANDLING section of libpmemcto(7). pmemcto_check() will return -1 and set errno if it cannot perform the consistency check due to other errors. pmemcto_check() opens the given path read-only so it never makes any changes to the file. This function is not supported on Device DAX.

RETURN VALUE

On success, pmemcto_create() returns a PMEMctopool* handle to the close-to-open persistence memory pool. On error, it returns NULL and sets errno appropriately.

On success, pmemcto_open() returns a PMEMctopool* handle that can be used with most of the functions in libpmemcto(7). On error, it returns NULL and sets errno appropriately.

The pmemcto_close() function returns no value.

pmemcto_check() returns 1 if the memory pool is found to be consistent. If the check is successfully performed but the pool is found to be inconsistent, pmemcto_check() returns 0. If the consistency check cannot be performed, pmemcto_check() returns -1 and sets errno appropriately. This includes the case where layout is non-NULL and does not match the layout string given when the pool was created.

ERRORS

EINVAL “layout” string does not match the layout stored in pool header.

EINVAL “layout” string is longer than PMEMCTO_MAX_LAYOUT.

EINVAL poolsize is less than PMEMCTO_MIN_POOL.

EINVAL Invalid format of the pool set file.

EINVAL Invalid pool header.

EEXIST path passed to pmemcto_create() points to a pool set file, but poolsize is not zero.

EEXIST path passed to pmemcto_create() points to an existing file, but poolsize is not zero.

EEXIST path passed to pmemcto_create() points to an existing file, which is not-empty.

EAGAIN The pmemcto pool pointed by path is already open.

EACCES No write access permission to the pool file(s).

ENOMEM The pool cannot be mapped at the address it was created.

CAVEATS

Not all file systems support posix_fallocate(3). pmemcto_create() will fail if the underlying file system does not support posix_fallocate(3).

BUGS

Unlike libpmemobj(7), data replication is not supported in libpmemcto(7). Thus, it is not allowed to specify replica sections in pool set files.

SEE ALSO

ndctl-create-namespace(1), pmempool-create(1), jemalloc(3), poolset(5), libpmemcto(7), libpmemobj(7) and <http://pmem.io>