---
layout: manual
Content-Style: 'text/css'
title: _MP(PMEMBLK_CREATE, 3)
collection: libpmemblk
header: PMDK
date: pmemblk API version 1.1
...

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[comment]: <> (pmemblk_create.3 -- man page for libpmemblk create, open, close and validate functions)

[NAME](#name)<br />
[SYNOPSIS](#synopsis)<br />
[DESCRIPTION](#description)<br />
[RETURN VALUE](#return-value)<br />
[SEE ALSO](#see-also)<br />


# NAME #

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


# SYNOPSIS #

```c
#include <libpmemblk.h>

_UWFUNCR1(PMEMblkpool, *pmemblk_create, *path, =q=size_t bsize,
		size_t poolsize, mode_t mode=e=)
_UWFUNCR1(PMEMblkpool, *pmemblk_open, *path, size_t bsize)
void pmemblk_close(PMEMblkpool *pbp);
_UWFUNCR1(int, pmemblk_check, *path, size_t bsize)
```

_UNICODE()


# DESCRIPTION #

The _UW(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 _UW(pmemblk_create), and then specifying *poolsize* as zero. In
this case _UW(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 _UW(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 _UW(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 _UW(pmemblk_open) function opens an existing block memory pool.
As with _UW(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,
_UW(pmemblk_open) will verify that the given block size matches the block
size used when the pool was created. Otherwise, _UW(pmemblk_open) will open
the pool without verifying the block size. The *bsize* can be determined
using the **pmemblk_bsize**(3) function.

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 _UW(pmemblk_open) as described above.

The _UW(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). _UW(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, _UW(pmemblk_create) returns a *PMEMblkpool\** handle to the block
memory pool. On error, it returns NULL and sets *errno* appropriately.

On success, _UW(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.

_UW(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,
_UW(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, _UW(pmemblk_check) returns -1 and sets
*errno* appropriately.


# CAVEATS #

Not all file systems support **posix_fallocate**(3). _UW(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 **<http://pmem.io>**
