1() PMDK Programmer's Manual ()
2
6 libpmempool - persistent memory pool management library
7 NOTE: Support for Windows and FreeBSD deprecated since PMDK
9 1.13.0 release and will be removed in the PMDK 1.14.0 release.
10
12 #include <libpmempool.h>
13 cc -std=gnu99 ... -lpmempool -lpmem
14 Library API versioning:
16 const char *pmempool_check_version(
17 unsigned major_required,
18 unsigned minor_required);
19 Error handling:
21 const char *pmempool_errormsg(void);
22 Other library functions:
24 A description of other libpmempool functions can be found on the fol‐
25 lowing manual pages:
26 • health check functions: pmempool_check_init(3)
28 • pool set synchronization and transformation: pmempool_sync(3)
30 • pool set management functions: pmempool_rm(3)
32 • toggle or query pool set features: pmempool_feature_query(3)
34
36 libpmempool provides a set of utilities for off-line analysis and ma‐
37 nipulation of a pool. A pool in this manpage means a pmemobj pool,
38 pmemblk pool, pmemlog pool or BTT layout, independent of the underlying
39 storage. Some libpmempool functions are required to work without any
40 impact on the pool but some may create a new or modify an existing
41 pool.
42 libpmempool is for applications that need high reliability or built-in
44 troubleshooting. It may be useful for testing and debugging purposes
45 also.
46 libpmempool introduces functionality of pool set health check, synchro‐
48 nization, transformation and removal.
49
51 libpmempool relies on the library destructor being called from the main
52 thread. For this reason, all functions that might trigger destruction
53 (e.g. dlclose(3)) should be called in the main thread. Otherwise some
54 of the resources associated with that thread might not be cleaned up
55 properly.
56 libpmempool requires the -std=gnu99 compilation flag to build properly.
58
60 This section describes how the library API is versioned, allowing ap‐
61 plications to work with an evolving API.
62 The pmempool_check_version() function is used to see if the installed
64 libpmempool supports the version of the library API required by an ap‐
65 plication. The easiest way to do this for the application is to supply
66 the compile-time version information, supplied by defines in <libpmem‐
67 pool.h>, like this:
68 reason = pmempool_check_version(PMEMPOOL_MAJOR_VERSION,
70 PMEMPOOL_MINOR_VERSION);
71 if (reason != NULL) {
72 /* version check failed, reason string tells you why */
73 }
74 Any mismatch in the major version number is considered a failure, but a
76 library with a newer minor version number will pass this check since
77 increasing minor versions imply backwards compatibility.
78 An application can also check specifically for the existence of an in‐
80 terface by checking for the version where that interface was intro‐
81 duced. These versions are documented in this man page as follows: un‐
82 less otherwise specified, all interfaces described here are available
83 in version 1.0 of the library. Interfaces added after version 1.0 will
84 contain the text introduced in version x.y in the section of this manu‐
85 al describing the feature.
86 When the version check performed by pmempool_check_version() is suc‐
88 cessful, the return value is NULL. Otherwise the return value is a
89 static string describing the reason for failing the version check. The
90 string returned by pmempool_check_version() must not be modified or
91 freed.
92
94 If an error is detected during the call to a libpmempool function, the
95 application may retrieve an error message describing the reason for the
96 failure from pmempool_errormsg(). This function returns a pointer to a
97 static buffer containing the last error message logged for the current
98 thread. If errno was set, the error message may include a description
99 of the corresponding error code as returned by strerror(3). The error
100 message buffer is thread-local; errors encountered in one thread do not
101 affect its value in other threads. The buffer is never cleared by any
102 library function; its content is significant only when the return value
103 of the immediately preceding call to a libpmempool function indicated
104 an error, or if errno was set. The application must not modify or free
105 the error message string, but it may be modified by subsequent calls to
106 other library functions.
107 Two versions of libpmempool are typically available on a development
109 system. The normal version, accessed when a program is linked using
110 the -lpmempool option, is optimized for performance. That version
111 skips checks that impact performance and never logs any trace informa‐
112 tion or performs any run-time assertions.
113 A second version of libpmempool, accessed when a program uses the li‐
115 braries under /usr/lib/pmdk_debug, contains run-time assertions and
116 trace points. The typical way to access the debug version is to set
117 the environment variable LD_LIBRARY_PATH to /usr/lib/pmdk_debug or
118 /usr/lib64/pmdk_debug, as appropriate. Debugging output is controlled
119 using the following environment variables. These variables have no ef‐
120 fect on the non-debug version of the library.
121 • PMEMPOOL_LOG_LEVEL
123 The value of PMEMPOOL_LOG_LEVEL enables trace points in the debug ver‐
125 sion of the library, as follows:
126 • 0 - This is the default level when PMEMPOOL_LOG_LEVEL is not set. No
128 log messages are emitted at this level.
129 • 1 - Additional details on any errors detected are logged (in addition
131 to returning the errno-based errors as usual). The same information
132 may be retrieved using pmempool_errormsg().
133 • 2 - A trace of basic operations is logged.
135 • 3 - Enables a very verbose amount of function call tracing in the li‐
137 brary.
138 • 4 - Enables voluminous and fairly obscure tracing information that is
140 likely only useful to the libpmempool developers.
141 Unless PMEMPOOL_LOG_FILE is set, debugging output is written to stderr.
143 • PMEMPOOL_LOG_FILE
145 Specifies the name of a file where all logging information should be
147 written. If the last character in the name is “-”, the PID of the cur‐
148 rent process will be appended to the file name when the log file is
149 created. If PMEMPOOL_LOG_FILE is not set, output is written to stderr.
150
152 The following example illustrates how the libpmempool API is used. The
153 program detects the type and checks consistency of given pool. If
154 there are any issues detected, the pool is automatically repaired.
155 #include <stddef.h>
157 #include <unistd.h>
158 #include <stdlib.h>
159 #include <stdio.h>
160 #include <libpmempool.h>
161 #define PATH "./pmem-fs/myfile"
163 #define CHECK_FLAGS (PMEMPOOL_CHECK_FORMAT_STR|PMEMPOOL_CHECK_REPAIR|\
164 PMEMPOOL_CHECK_VERBOSE)
165 int
167 main(int argc, char *argv[])
168 {
169 PMEMpoolcheck *ppc;
170 struct pmempool_check_status *status;
171 enum pmempool_check_result ret;
172 /* arguments for check */
174 struct pmempool_check_args args = {
175 .path = PATH,
176 .backup_path = NULL,
177 .pool_type = PMEMPOOL_POOL_TYPE_DETECT,
178 .flags = CHECK_FLAGS
179 };
180 /* initialize check context */
182 if ((ppc = pmempool_check_init(&args, sizeof(args))) == NULL) {
183 perror("pmempool_check_init");
184 exit(EXIT_FAILURE);
185 }
186 /* perform check and repair, answer 'yes' for each question */
188 while ((status = pmempool_check(ppc)) != NULL) {
189 switch (status->type) {
190 case PMEMPOOL_CHECK_MSG_TYPE_ERROR:
191 printf("%s\n", status->str.msg);
192 break;
193 case PMEMPOOL_CHECK_MSG_TYPE_INFO:
194 printf("%s\n", status->str.msg);
195 break;
196 case PMEMPOOL_CHECK_MSG_TYPE_QUESTION:
197 printf("%s\n", status->str.msg);
198 status->str.answer = "yes";
199 break;
200 default:
201 pmempool_check_end(ppc);
202 exit(EXIT_FAILURE);
203 }
204 }
205 /* finalize the check and get the result */
207 ret = pmempool_check_end(ppc);
208 switch (ret) {
209 case PMEMPOOL_CHECK_RESULT_CONSISTENT:
210 case PMEMPOOL_CHECK_RESULT_REPAIRED:
211 return 0;
212 default:
213 return 1;
214 }
215 }
216 See <https://pmem.io/pmdk/libpmempool> for more examples using the
218 libpmempool API.
219
221 libpmempool builds on the persistent memory programming model recom‐
222 mended by the SNIA NVM Programming Technical Work Group:
223 <https://snia.org/nvmp>
224
226 dlclose(3), pmempool_check_init(3), pmempool_feature_query(3), pmem‐
227 pool_rm(3), pmempool_sync(3), strerror(3), libpmem(7), libpmemblk(7),
228 libpmemlog(7), libpmemobj(7) and <https://pmem.io>**
229PMDK - 2023-06-05 ()