Ubuntu Manpage: libpmempool - persistent memory pool management library

Provided by: libpmempool-dev_1.11.1-3build1_amd64

NAME

       libpmempool - persistent memory pool management library

SYNOPSIS

              #include <libpmempool.h>
              cc -std=gnu99 ... -lpmempool -lpmem

   Library API versioning:
              const char *pmempool_check_version(
                  unsigned major_required,
                  unsigned minor_required);

   Error handling:
              const char *pmempool_errormsg(void);

   Other library functions:
       A description of other libpmempool functions can be found on the following manual pages:

       • health check functions: pmempool_check_init(3)

       • pool set synchronization and transformation: pmempool_sync(3)

       • pool set management functions: pmempool_rm(3)

       • toggle or query pool set features: pmempool_feature_query(3)

DESCRIPTION

       libpmempool provides a set of utilities for off-line analysis and manipulation of a pool.  A pool in this
       manpage  means  a  pmemobj  pool, pmemblk pool, pmemlog pool or BTT layout, independent of the underlying
       storage.  Some libpmempool functions are required to work without any impact on the  pool  but  some  may
       create a new or modify an existing pool.

       libpmempool is for applications that need high reliability or built-in troubleshooting.  It may be useful
       for testing and debugging purposes also.

       libpmempool  introduces  functionality  of pool set health check, synchronization, transformation and re‐
       moval.

CAVEATS

       libpmempool relies on the library destructor being called from the main thread.   For  this  reason,  all
       functions  that might trigger destruction (e.g.  dlclose(3)) should be called in the main thread.  Other‐
       wise some of the resources associated with that thread might not be cleaned up properly.

       libpmempool requires the -std=gnu99 compilation flag to build properly.

LIBRARY API VERSIONING

       This section describes how the library API is versioned, allowing applications to work with  an  evolving
       API.

       The pmempool_check_version() function is used to see if the installed libpmempool supports the version of
       the  library API required by an application.  The easiest way to do this for the application is to supply
       the compile-time version information, supplied by defines in <libpmempool.h>, like this:

              reason = pmempool_check_version(PMEMPOOL_MAJOR_VERSION,
                                              PMEMPOOL_MINOR_VERSION);
              if (reason != NULL) {
                  /* version check failed, reason string tells you why */
              }

       Any mismatch in the major version number is considered a failure, but a library with a newer  minor  ver‐
       sion number will pass this check since increasing minor versions imply backwards compatibility.

       An  application can also check specifically for the existence of an interface by checking for the version
       where that interface was introduced.  These versions are documented in this man page as  follows:  unless
       otherwise  specified,  all interfaces described here are available in version 1.0 of the library.  Inter‐
       faces added after version 1.0 will contain the text introduced in version x.y in the section of this man‐
       ual describing the feature.

       When the version check performed by pmempool_check_version() is successful, the  return  value  is  NULL.
       Otherwise  the  return value is a static string describing the reason for failing the version check.  The
       string returned by pmempool_check_version() must not be modified or freed.

DEBUGGING AND ERROR HANDLING

       If an error is detected during the call to a libpmempool function, the application may retrieve an  error
       message  describing the reason for the failure from pmempool_errormsg().  This function returns a pointer
       to a static buffer containing the last error message logged for the current thread.  If  errno  was  set,
       the  error  message may include a description of the corresponding error code as returned by strerror(3).
       The error message buffer is thread-local; errors encountered in one thread do not  affect  its  value  in
       other threads.  The buffer is never cleared by any library function; its content is significant only when
       the  return  value  of the immediately preceding call to a libpmempool function indicated an error, or if
       errno was set.  The application must not modify or free the error message string, but it may be  modified
       by subsequent calls to other library functions.

       Two  versions  of  libpmempool  are typically available on a development system.  The normal version, ac‐
       cessed when a program is linked using the -lpmempool option, is optimized for performance.  That  version
       skips checks that impact performance and never logs any trace information or performs any run-time asser‐
       tions.

       A  second  version  of libpmempool, accessed when a program uses the libraries under /usr/lib/pmdk_debug,
       contains run-time assertions and trace points.  The typical way to access the debug version is to set the
       environment variable LD_LIBRARY_PATH to /usr/lib/pmdk_debug  or  /usr/lib64/pmdk_debug,  as  appropriate.
       Debugging output is controlled using the following environment variables.  These variables have no effect
       on the non-debug version of the library.

              NOTE:  On Debian/Ubuntu systems, this extra debug version of the library is shipped in the respec‐
              tive -debug Debian package and placed in the /usr/lib/$ARCH/pmdk_dbg/ directory.

       • PMEMPOOL_LOG_LEVEL

       The value of PMEMPOOL_LOG_LEVEL enables trace points in the debug version of the library, as follows:

       • 0 - This is the default level when PMEMPOOL_LOG_LEVEL is not set.  No log messages are emitted at  this
         level.

       • 1  - Additional details on any errors detected are logged (in addition to returning the errno-based er‐
         rors as usual).  The same information may be retrieved using pmempool_errormsg().

       • 2 - A trace of basic operations is logged.

       • 3 - Enables a very verbose amount of function call tracing in the library.

       • 4 - Enables voluminous and fairly obscure tracing information that is likely only useful to  the  libp‐
         mempool developers.

       Unless PMEMPOOL_LOG_FILE is set, debugging output is written to stderr.

       • PMEMPOOL_LOG_FILE

       Specifies  the  name of a file where all logging information should be written.  If the last character in
       the name is “-”, the PID of the current process will be appended to the file name when the  log  file  is
       created.  If PMEMPOOL_LOG_FILE is not set, output is written to stderr.

EXAMPLE

       The  following  example  illustrates  how  the libpmempool API is used.  The program detects the type and
       checks consistency of given pool.  If there are any issues detected, the pool is automatically repaired.

              #include <stddef.h>
              #include <unistd.h>
              #include <stdlib.h>
              #include <stdio.h>
              #include <libpmempool.h>

              #define PATH "./pmem-fs/myfile"
              #define CHECK_FLAGS (PMEMPOOL_CHECK_FORMAT_STR|PMEMPOOL_CHECK_REPAIR|\
                                   PMEMPOOL_CHECK_VERBOSE)

              int
              main(int argc, char *argv[])
              {
                  PMEMpoolcheck *ppc;
                  struct pmempool_check_status *status;
                  enum pmempool_check_result ret;

                  /* arguments for check */
                  struct pmempool_check_args args = {
                      .path       = PATH,
                      .backup_path    = NULL,
                      .pool_type  = PMEMPOOL_POOL_TYPE_DETECT,
                      .flags      = CHECK_FLAGS
                  };

                  /* initialize check context */
                  if ((ppc = pmempool_check_init(&args, sizeof(args))) == NULL) {
                      perror("pmempool_check_init");
                      exit(EXIT_FAILURE);
                  }

                  /* perform check and repair, answer 'yes' for each question */
                  while ((status = pmempool_check(ppc)) != NULL) {
                      switch (status->type) {
                      case PMEMPOOL_CHECK_MSG_TYPE_ERROR:
                          printf("%s\n", status->str.msg);
                          break;
                      case PMEMPOOL_CHECK_MSG_TYPE_INFO:
                          printf("%s\n", status->str.msg);
                          break;
                      case PMEMPOOL_CHECK_MSG_TYPE_QUESTION:
                          printf("%s\n", status->str.msg);
                          status->str.answer = "yes";
                          break;
                      default:
                          pmempool_check_end(ppc);
                          exit(EXIT_FAILURE);
                      }
                  }

                  /* finalize the check and get the result */
                  ret = pmempool_check_end(ppc);
                  switch (ret) {
                      case PMEMPOOL_CHECK_RESULT_CONSISTENT:
                      case PMEMPOOL_CHECK_RESULT_REPAIRED:
                          return 0;
                      default:
                          return 1;
                  }
              }

       See <https://pmem.io/pmdk/libpmempool> for more examples using the libpmempool API.

ACKNOWLEDGEMENTS

       libpmempool builds on the persistent memory programming model recommended by  the  SNIA  NVM  Programming
       Technical Work Group: <https://snia.org/nvmp>

NAME

SYNOPSIS

DESCRIPTION

CAVEATS

LIBRARY API VERSIONING

DEBUGGING AND ERROR HANDLING

EXAMPLE

ACKNOWLEDGEMENTS

SEE ALSO