NAME

       pmemobj_open(),     pmemobj_create(),     pmemobj_close(),    pmemobj_check()    pmemobj_set_user_data(),
       pmemobj_get_user_data() - create, open, close and validate persistent memory transactional object store

SYNOPSIS

              #include <libpmemobj.h>

              PMEMobjpool *pmemobj_open(const char *path, const char *layout);
              PMEMobjpool *pmemobj_create(const char *path, const char *layout,
                  size_t poolsize, mode_t mode);
              void pmemobj_close(PMEMobjpool *pop);
              int pmemobj_check(const char *path, const char *layout);

              void pmemobj_set_user_data(PMEMobjpool *pop, void *data);
              void *pmemobj_get_user_data(PMEMobjpool *pop);

DESCRIPTION

       To use the pmem-resident transactional object store provided by libpmemobj(7), a memory pool  must  first
       be  created  with  the  pmemobj_create() function described below.  Existing pools may be opened with the
       pmemobj_open() function.

       As of libpmemobj 1.11, these functions are thread-safe; be careful if you have to use earlier versions of
       the library.

       Once  created,  the memory pool is represented by an opaque handle, of type PMEMobjpool*, which is passed
       to most of the other libpmemobj(7) functions.  Internally, libpmemobj(7) will use either  pmem_persist(3)
       or msync(2) when it needs to flush changes, depending on whether the memory pool appears to be persistent
       memory or a regular file (see the pmem_is_pmem(3) function in libpmem(7) for more information).  There is
       no  need  for  applications  to  flush  changes  directly  when  using  the object memory API provided by
       libpmemobj(7).

       The pmemobj_create() function creates a transactional object store with the given total  poolsize.   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 libpmemobj(7), but may be used as a check
       when  pmemobj_open()  is  called.  The layout name, including the terminating null byte (`\0'), cannot be
       longer than PMEMOBJ_MAX_LAYOUT as defined in <libpmemobj.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 pmemobj_create(),  and  then  specifying  poolsize  as  zero.   In  this  case
       pmemobj_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 transactional object store is defined in
       <libpmemobj.h> as PMEMOBJ_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 pmemobj memory pool could be limited by
       the capacity of a single memory device.  libpmemobj(7) allows building persistent memory resident  object
       store  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 pmemobj_create(); however, the recommended
       method for creating pool sets is with the pmempool(1) utility.

       When creating a pool set consisting of multiple files, the path argument passed to pmemobj_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.

       The set file is a plain text file, the structure of which is described in poolset(5).

       The  pmemobj_open()  function  opens  an existing object store memory pool.  Similar to pmemobj_create(),
       path must identify either an existing obj memory pool file, or the set file used to create  a  pool  set.
       If  layout  is non-NULL, it is compared to the layout name provided to pmemobj_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.

       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 pmemobj_close() function closes the memory pool indicated by pop and deletes the memory pool  handle.
       The  object store itself lives on in the file that contains it and may be re-opened at a later time using
       pmemobj_open() as described above.

       The pmemobj_check() function performs a consistency check of the file indicated by path.  pmemobj_check()
       opens the given path read-only so it never makes any changes to the file.  This function is not supported
       on Device DAX.

       The pmemobj_set_user_data() function associates custom volatile state, represented by pointer data,  with
       the  given  pool  pop.   This  state can later be retrieved using pmemobj_get_user_data() function.  This
       state does not survive pool  close.   If  pmemobj_set_user_data()  was  not  called  for  a  given  pool,
       pmemobj_get_user_data() will return NULL.

RETURN VALUE

       The  pmemobj_create()  function  returns  a  memory  pool handle to be used with most of the functions in
       libpmemobj(7).  On error it returns NULL and sets errno appropriately.

       The pmemobj_open() function returns a memory pool handle to  be  used  with  most  of  the  functions  in
       libpmemobj(7).   If  an  error prevents the pool from being opened, or if the given layout does not match
       the pool’s layout, pmemobj_open() returns NULL and sets errno appropriately.

       The pmemobj_close() function returns no value.

       The pmemobj_check() function returns 1 if the memory pool is found to be consistent.  Any inconsistencies
       found  will  cause pmemobj_check() to return 0, in which case the use of the file with libpmemobj(7) will
       result in undefined behavior.  The debug version of libpmemobj(7)  will  provide  additional  details  on
       inconsistencies  when  PMEMOBJ_LOG_LEVEL  is at least 1, as described in the DEBUGGING AND ERROR HANDLING
       section in libpmemobj(7).  pmemobj_check() returns -1 and sets errno if it cannot perform the consistency
       check due to other errors.

CAVEATS

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

SEE ALSO

       creat(2), msync(2), pmem_is_pmem(3), pmem_persist(3), posix_fallocate(3), libpmem(7),  libpmemobj(7)  and
       <https://pmem.io>