PMEMBLK_CREATE(3)

NAME

pmemblk_create(), pmemblk_open(), pmemblk_close(), pmemblk_check() - create, open, close and validate block pool

SYNOPSIS

    #include <libpmemblk.h>

    PMEMblkpool *pmemblk_create(const char *path, size_t bsize,
            size_t poolsize, mode_t mode);
    PMEMblkpool *pmemblk_open(const char *path, size_t bsize);
    void pmemblk_close(PMEMblkpool *pbp);
    int pmemblk_check(const char *path, size_t bsize);

DESCRIPTION

The pmemblk_create() function creates a block memory pool with the given total poolsize, divided into as many elements of size bsize as will fit in the pool. Since the transactional nature of a block memory pool requires some space overhead in the memory pool, the resulting number of available blocks is less than poolsize/bsize, and is made available to the caller via the pmemblk_nblock(3) function. Given the specifics of the implementation, the number of available blocks for the user cannot be less than 256. This translates to at least 512 internal blocks. path specifies the name of the memory pool file to be created. 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 pmemblk_create(), and then specifying poolsize as zero. In this case pmemblk_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 net pool size of a pool file is equal to the file size. The minimum net pool size allowed by the library for a block pool is defined in <libpmemblk.h> as PMEMBLK_MIN_POOL. bsize can be any non-zero value; however, libpmemblk will silently round up the given size to PMEMBLK_MIN_BLK, as defined in <libpmemblk.h>.

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 pmemblk memory pool could be limited by the capacity of a single memory device. libpmemblk(7) allows building a persistent memory resident array 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 pmemblk_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 pmemblk_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 mode argument 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 pmemblk_open() function opens an existing block memory pool. As with pmemblk_create(), path must identify either an existing block memory pool file, or the set file used to create a pool set. The application must have permission to open the file and memory map the file or pool set with read/write permissions. If bsize is non-zero, pmemblk_open() will verify that the given block size matches the block size used when the pool was created. Otherwise, pmemblk_open() will open the pool without verifying the block size. The bsize can be determined using the pmemblk_bsize(3) function.

Be aware that if the pool contains bad blocks inside, opening can be aborted by the SIGBUS signal, because currently the pool is not checked against bad blocks during opening. It can be turned on by setting the CHECK_BAD_BLOCKS compat feature. For details see description of this feature in pmempool-feature(1).

The pmemblk_close() function closes the memory pool indicated by pbp and deletes the memory pool handle. The block memory pool itself lives on in the file that contains it and may be re-opened at a later time using pmemblk_open() as described above.

The pmemblk_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 libpmemblk will result in undefined behavior. The debug version of libpmemblk will provide additional details on inconsistencies when PMEMBLK_LOG_LEVEL is at least 1, as described in the DEBUGGING AND ERROR HANDLING section in libpmemblk(7). pmemblk_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, pmemblk_create() returns a PMEMblkpool* handle to the block memory pool. On error, it returns NULL and sets errno appropriately.

On success, pmemblk_open() returns a PMEMblkpool* handle that can be used with most of the functions in libpmemblk(7). On error, it returns NULL and sets errno appropriately. Possible errors include:

•   failure to open path

•   path specifies a set file and any of the pool set files cannot be opened

•   path specifies a set file and the actual size of any file does not match the corresponding part size defined in the set file

•   bsize is non-zero and does not match the block size given when the pool was created. errno is set to EINVAL in this case.

The pmemblk_close() function returns no value.

pmemblk_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, pmemblk_check() returns 0. This includes the case where bsize is non-zero and does not match the block size given when the pool was created. If the consistency check cannot be performed, pmemblk_check() returns -1 and sets errno appropriately.

CAVEATS

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

SEE ALSO

pmempool(1), creat(2), pmemblk_nblock(3), posix_fallocate(3), poolset(5), libpmemblk(7) and <https://pmem.io>