1PMEMOBJ_OPEN(3) PMDK Programmer's Manual PMEMOBJ_OPEN(3)
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6 pmemobj_open(), pmemobj_create(), pmemobj_close(), pmemobj_check()
7 pmemobj_set_user_data(), pmemobj_get_user_data() - create, open, close
8 and validate persistent memory transactional object store
9
11 #include <libpmemobj.h>
12 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);
18 void pmemobj_set_user_data(PMEMobjpool *pop, void *data);
20 void *pmemobj_get_user_data(PMEMobjpool *pop);
21
23 To use the pmem-resident transactional object store provided by libp‐
24 memobj(7), a memory pool must first be created with the pmemobj_cre‐
25 ate() function described below. Existing pools may be opened with the
26 pmemobj_open() function.
27 As of libpmemobj 1.11, these functions are thread-safe; be careful if
29 you have to use earlier versions of the library.
30 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).
39 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.
60 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.
69 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.
73 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.
80 The set file is a plain text file, the structure of which is described
82 in poolset(5).
83 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.
92 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).
98 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.
103 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.
108 The pmemobj_set_user_data() function associates custom volatile state,
110 represented by pointer data, with the given pool pop. This state can
111 later be retrieved using pmemobj_get_user_data() function. This state
112 does not survive pool close. If pmemobj_set_user_data() was not called
113 for a given pool, pmemobj_get_user_data() will return NULL.
114
116 The pmemobj_create() function returns a memory pool handle to be used
117 with most of the functions in libpmemobj(7). On error it returns NULL
118 and sets errno appropriately.
119 The pmemobj_open() function returns a memory pool handle to be used
121 with most of the functions in libpmemobj(7). If an error prevents the
122 pool from being opened, or if the given layout does not match the
123 pool's layout, pmemobj_open() returns NULL and sets errno appropriate‐
124 ly.
125 The pmemobj_close() function returns no value.
127 The pmemobj_check() function returns 1 if the memory pool is found to
129 be consistent. Any inconsistencies found will cause pmemobj_check() to
130 return 0, in which case the use of the file with libpmemobj(7) will re‐
131 sult in undefined behavior. The debug version of libpmemobj(7) will
132 provide additional details on inconsistencies when PMEMOBJ_LOG_LEVEL is
133 at least 1, as described in the DEBUGGING AND ERROR HANDLING section in
134 libpmemobj(7). pmemobj_check() returns -1 and sets errno if it cannot
135 perform the consistency check due to other errors.
136
138 Not all file systems support posix_fallocate(3). pmemobj_create() will
139 fail if the underlying file system does not support posix_fallocate(3).
140
142 creat(2), msync(2), pmem_is_pmem(3), pmem_persist(3), posix_fallo‐
143 cate(3), libpmem(7), libpmemobj(7) and <https://pmem.io>
144PMDK - pmemobj API version 2.3 2022-08-25 PMEMOBJ_OPEN(3)