1LIBPMEMPOOL(7) PMDK Programmer's Manual LIBPMEMPOOL(7)
2
6 libpmempool - persistent memory pool management library
7
9 #include <libpmempool.h>
10 cc -std=gnu99 ... -lpmempool -lpmem
11 Library API versioning:
13 const char *pmempool_check_version(
14 unsigned major_required,
15 unsigned minor_required);
16 Error handling:
18 const char *pmempool_errormsg(void);
19 Other library functions:
21 A description of other libpmempool functions can be found on the fol‐
22 lowing manual pages:
23 • health check functions: pmempool_check_init(3)
25 • pool set synchronization and transformation: pmempool_sync(3)
27 • pool set management functions: pmempool_rm(3)
29 • toggle or query pool set features: pmempool_feature_query(3)
31
33 libpmempool provides a set of utilities for off-line analysis and ma‐
34 nipulation of a pool. A pool in this manpage means a pmemobj pool,
35 pmemblk pool, pmemlog pool or BTT layout, independent of the underlying
36 storage. Some libpmempool functions are required to work without any
37 impact on the pool but some may create a new or modify an existing
38 pool.
39 libpmempool is for applications that need high reliability or built-in
41 troubleshooting. It may be useful for testing and debugging purposes
42 also.
43 libpmempool introduces functionality of pool set health check, synchro‐
45 nization, transformation and removal.
46
48 libpmempool relies on the library destructor being called from the main
49 thread. For this reason, all functions that might trigger destruction
50 (e.g. dlclose(3)) should be called in the main thread. Otherwise some
51 of the resources associated with that thread might not be cleaned up
52 properly.
53 libpmempool requires the -std=gnu99 compilation flag to build properly.
55
57 This section describes how the library API is versioned, allowing ap‐
58 plications to work with an evolving API.
59 The pmempool_check_version() function is used to see if the installed
61 libpmempool supports the version of the library API required by an ap‐
62 plication. The easiest way to do this for the application is to supply
63 the compile-time version information, supplied by defines in <libpmem‐
64 pool.h>, like this:
65 reason = pmempool_check_version(PMEMPOOL_MAJOR_VERSION,
67 PMEMPOOL_MINOR_VERSION);
68 if (reason != NULL) {
69 /* version check failed, reason string tells you why */
70 }
71 Any mismatch in the major version number is considered a failure, but a
73 library with a newer minor version number will pass this check since
74 increasing minor versions imply backwards compatibility.
75 An application can also check specifically for the existence of an in‐
77 terface by checking for the version where that interface was intro‐
78 duced. These versions are documented in this man page as follows: un‐
79 less otherwise specified, all interfaces described here are available
80 in version 1.0 of the library. Interfaces added after version 1.0 will
81 contain the text introduced in version x.y in the section of this manu‐
82 al describing the feature.
83 When the version check performed by pmempool_check_version() is suc‐
85 cessful, the return value is NULL. Otherwise the return value is a
86 static string describing the reason for failing the version check. The
87 string returned by pmempool_check_version() must not be modified or
88 freed.
89
91 If an error is detected during the call to a libpmempool function, the
92 application may retrieve an error message describing the reason for the
93 failure from pmempool_errormsg(). This function returns a pointer to a
94 static buffer containing the last error message logged for the current
95 thread. If errno was set, the error message may include a description
96 of the corresponding error code as returned by strerror(3). The error
97 message buffer is thread-local; errors encountered in one thread do not
98 affect its value in other threads. The buffer is never cleared by any
99 library function; its content is significant only when the return value
100 of the immediately preceding call to a libpmempool function indicated
101 an error, or if errno was set. The application must not modify or free
102 the error message string, but it may be modified by subsequent calls to
103 other library functions.
104 Two versions of libpmempool are typically available on a development
106 system. The normal version, accessed when a program is linked using
107 the -lpmempool option, is optimized for performance. That version
108 skips checks that impact performance and never logs any trace informa‐
109 tion or performs any run-time assertions.
110 A second version of libpmempool, accessed when a program uses the li‐
112 braries under /usr/lib/pmdk_debug, contains run-time assertions and
113 trace points. The typical way to access the debug version is to set
114 the environment variable LD_LIBRARY_PATH to /usr/lib/pmdk_debug or
115 /usr/lib64/pmdk_debug, as appropriate. Debugging output is controlled
116 using the following environment variables. These variables have no ef‐
117 fect on the non-debug version of the library.
118 • PMEMPOOL_LOG_LEVEL
120 The value of PMEMPOOL_LOG_LEVEL enables trace points in the debug ver‐
122 sion of the library, as follows:
123 • 0 - This is the default level when PMEMPOOL_LOG_LEVEL is not set. No
125 log messages are emitted at this level.
126 • 1 - Additional details on any errors detected are logged (in addition
128 to returning the errno-based errors as usual). The same information
129 may be retrieved using pmempool_errormsg().
130 • 2 - A trace of basic operations is logged.
132 • 3 - Enables a very verbose amount of function call tracing in the li‐
134 brary.
135 • 4 - Enables voluminous and fairly obscure tracing information that is
137 likely only useful to the libpmempool developers.
138 Unless PMEMPOOL_LOG_FILE is set, debugging output is written to stderr.
140 • PMEMPOOL_LOG_FILE
142 Specifies the name of a file where all logging information should be
144 written. If the last character in the name is “-”, the PID of the cur‐
145 rent process will be appended to the file name when the log file is
146 created. If PMEMPOOL_LOG_FILE is not set, output is written to stderr.
147
149 The following example illustrates how the libpmempool API is used. The
150 program detects the type and checks consistency of given pool. If
151 there are any issues detected, the pool is automatically repaired.
152 #include <stddef.h>
154 #include <unistd.h>
155 #include <stdlib.h>
156 #include <stdio.h>
157 #include <libpmempool.h>
158 #define PATH "./pmem-fs/myfile"
160 #define CHECK_FLAGS (PMEMPOOL_CHECK_FORMAT_STR|PMEMPOOL_CHECK_REPAIR|\
161 PMEMPOOL_CHECK_VERBOSE)
162 int
164 main(int argc, char *argv[])
165 {
166 PMEMpoolcheck *ppc;
167 struct pmempool_check_status *status;
168 enum pmempool_check_result ret;
169 /* arguments for check */
171 struct pmempool_check_args args = {
172 .path = PATH,
173 .backup_path = NULL,
174 .pool_type = PMEMPOOL_POOL_TYPE_DETECT,
175 .flags = CHECK_FLAGS
176 };
177 /* initialize check context */
179 if ((ppc = pmempool_check_init(&args, sizeof(args))) == NULL) {
180 perror("pmempool_check_init");
181 exit(EXIT_FAILURE);
182 }
183 /* perform check and repair, answer 'yes' for each question */
185 while ((status = pmempool_check(ppc)) != NULL) {
186 switch (status->type) {
187 case PMEMPOOL_CHECK_MSG_TYPE_ERROR:
188 printf("%s\n", status->str.msg);
189 break;
190 case PMEMPOOL_CHECK_MSG_TYPE_INFO:
191 printf("%s\n", status->str.msg);
192 break;
193 case PMEMPOOL_CHECK_MSG_TYPE_QUESTION:
194 printf("%s\n", status->str.msg);
195 status->str.answer = "yes";
196 break;
197 default:
198 pmempool_check_end(ppc);
199 exit(EXIT_FAILURE);
200 }
201 }
202 /* finalize the check and get the result */
204 ret = pmempool_check_end(ppc);
205 switch (ret) {
206 case PMEMPOOL_CHECK_RESULT_CONSISTENT:
207 case PMEMPOOL_CHECK_RESULT_REPAIRED:
208 return 0;
209 default:
210 return 1;
211 }
212 }
213 See <https://pmem.io/pmdk/libpmempool> for more examples using the
215 libpmempool API.
216
218 libpmempool builds on the persistent memory programming model recom‐
219 mended by the SNIA NVM Programming Technical Work Group:
220 <https://snia.org/nvmp>
221
223 dlclose(3), pmempool_check_init(3), pmempool_feature_query(3), pmem‐
224 pool_rm(3), pmempool_sync(3), strerror(3), libpmem(7), libpmemblk(7),
225 libpmemlog(7), libpmemobj(7) and <https://pmem.io>**
226PMDK - pmempool API version 1.3 2022-05-24 LIBPMEMPOOL(7)