Provided by: libpmempool-dev_1.4.1-0ubuntu1~18.04.1_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)
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 removal.
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. Otherwise 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 version 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. Interfaces added after version 1.0 will contain
the text introduced in version x.y in the section of this manual 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, accessed 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 assertions.
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.
• 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 errors 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 libpmempool 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.
NOTE: on Ubuntu systems, this extra debug version of the library is shipped in the
respective -debug Debian package and placed in the /usr/lib/$ARCH/pmdk_dbg/
directory.
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 <http://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: <http://snia.org/nvmp>
SEE ALSO
dlclose(3), pmempool_check_init(3), pmempool_rm(3), pmempool_sync(3), strerror(3),
libpmem(7), libpmemblk(7), libpmemcto(7), libpmemlog(7), libpmemobj(7) and
<http://pmem.io>