pmemobj_open(3)

1PMEMOBJ_OPEN(3)            PMDK Programmer's Manual            PMEMOBJ_OPEN(3)
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NAME

6       pmemobj_open(),  pmemobj_create(),  pmemobj_close(),  pmemobj_check() -
7       create, open, close and validate persistent memory transactional object
8       store
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SYNOPSIS

11              #include <libpmemobj.h>
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13              PMEMobjpool *pmemobj_open(const char *path, const char *layout);
14              PMEMobjpool *pmemobj_create(const char *path, const char *layout,
15                  size_t poolsize, mode_t mode);
16              void pmemobj_close(PMEMobjpool *pop);
17              int pmemobj_check(const char *path, const char *layout);
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DESCRIPTION

20       To  use  the pmem-resident transactional object store provided by libp‐
21       memobj(7), a memory pool must first be created  with  the  pmemobj_cre‐
22       ate()  function described below.  Existing pools may be opened with the
23       pmemobj_open() function.
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25       None of the three functions described below is thread-safe with respect
26       to  any  other libpmemobj(7) functions.  In other words, when creating,
27       opening or deleting a pool, nothing else in the library can  happen  in
28       parallel,  and therefore these functions should be called from the main
29       thread.
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31       Once created, the memory pool is represented by an  opaque  handle,  of
32       type  PMEMobjpool*,  which is passed to most of the other libpmemobj(7)
33       functions.  Internally, libpmemobj(7) will use  either  pmem_persist(3)
34       or  msync(2)  when  it needs to flush changes, depending on whether the
35       memory pool appears to be persistent memory or a regular file (see  the
36       pmem_is_pmem(3) function in libpmem(7) for more information).  There is
37       no need for applications to flush changes directly when using  the  ob‐
38       ject memory API provided by libpmemobj(7).
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40       The pmemobj_create() function creates a transactional object store with
41       the given total poolsize.  path specifies the name of the  memory  pool
42       file  to be created.  layout specifies the application's layout type in
43       the form of a string.  The layout name is not interpreted by  libpmemo‐
44       bj(7),  but  may be used as a check when pmemobj_open() is called.  The
45       layout name, including the terminating  null  byte  (`\0'),  cannot  be
46       longer  than  PMEMOBJ_MAX_LAYOUT  as defined in <libpmemobj.h>.  A NULL
47       layout is equivalent to using an empty string as a layout  name.   mode
48       specifies  the  permissions to use when creating the file, as described
49       by creat(2).  The memory pool file is fully allocated to the size pool‐
50       size using posix_fallocate(3).  The caller may choose to take responsi‐
51       bility for creating the memory pool file by creating it before  calling
52       pmemobj_create(),  and  then specifying poolsize as zero.  In this case
53       pmemobj_create() will take the pool size from the size of the  existing
54       file and will verify that the file appears to be empty by searching for
55       any non-zero data in the pool header at the beginning of the file.  The
56       minimum  net pool size allowed by the library for a local transactional
57       object store is defined in <libpmemobj.h> as PMEMOBJ_MIN_POOL.  For re‐
58       mote  replicas  the minimum file size is defined in <librpmem.h> as RP‐
59       MEM_MIN_PART.
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61       Depending  on  the  configuration  of   the   system,   the   available
62       non-volatile  memory space may be divided into multiple memory devices.
63       In such case, the maximum size of the pmemobj memory pool could be lim‐
64       ited  by  the capacity of a single memory device.  libpmemobj(7) allows
65       building persistent memory resident object store spanning multiple mem‐
66       ory devices by creation of persistent memory pools consisting of multi‐
67       ple files, where each part of such a pool set may be stored on  a  dif‐
68       ferent memory device or pmem-aware filesystem.
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70       Creation of all the parts of the pool set can be done with pmemobj_cre‐
71       ate(); however, the recommended method for creating pool sets  is  with
72       the pmempool(1) utility.
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74       When  creating  a pool set consisting of multiple files, the path argu‐
75       ment passed to pmemobj_create() must point to the special set file that
76       defines  the  pool layout and the location of all the parts of the pool
77       set.  The poolsize argument must be 0.  The meaning of the  layout  and
78       mode  arguments  does not change, except that the same mode is used for
79       creation of all the parts of the pool set.
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81       The set file is a plain text file, the structure of which is  described
82       in poolset(5).
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84       The pmemobj_open() function opens an existing object store memory pool.
85       Similar to pmemobj_create(), path must identify either an existing  obj
86       memory pool file, or the set file used to create a pool set.  If layout
87       is non-NULL, it is compared to the layout name provided to pmemobj_cre‐
88       ate() when the pool was first created.  This can be used to verify that
89       the layout of the pool matches what was expected.  The application must
90       have permission to open the file and memory map it with read/write per‐
91       missions.
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93       Be aware that if the pool contains bad blocks inside,  opening  can  be
94       aborted by the SIGBUS signal, because currently the pool is not checked
95       against bad blocks during opening.  It can be turned on by setting  the
96       CHECK_BAD_BLOCKS  compat  feature.  For details see description of this
97       feature in pmempool-feature(1).
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99       The pmemobj_close() function closes the memory pool  indicated  by  pop
100       and  deletes  the memory pool handle.  The object store itself lives on
101       in the file that contains it and may be re-opened at a later time using
102       pmemobj_open() as described above.
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104       The  pmemobj_check()  function performs a consistency check of the file
105       indicated by path.  pmemobj_check() opens the given path  read-only  so
106       it never makes any changes to the file.  This function is not supported
107       on Device DAX.
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RETURN VALUE

110       The pmemobj_create() function returns a memory pool handle to  be  used
111       with  most of the functions in libpmemobj(7).  On error it returns NULL
112       and sets errno appropriately.
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114       The pmemobj_open() function returns a memory pool  handle  to  be  used
115       with  most of the functions in libpmemobj(7).  If an error prevents the
116       pool from being opened, or if the  given  layout  does  not  match  the
117       pool's  layout, pmemobj_open() returns NULL and sets errno appropriate‐
118       ly.
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120       The pmemobj_close() function returns no value.
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122       The pmemobj_check() function returns 1 if the memory pool is  found  to
123       be consistent.  Any inconsistencies found will cause pmemobj_check() to
124       return 0, in which case the use of the file with libpmemobj(7) will re‐
125       sult  in  undefined  behavior.  The debug version of libpmemobj(7) will
126       provide additional details on inconsistencies when PMEMOBJ_LOG_LEVEL is
127       at least 1, as described in the DEBUGGING AND ERROR HANDLING section in
128       libpmemobj(7).  pmemobj_check() returns -1 and sets errno if it  cannot
129       perform the consistency check due to other errors.
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CAVEATS

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

SYNOPSIS

DESCRIPTION

RETURN VALUE

CAVEATS

SEE ALSO