()

NAME
pmem_log_set_function() - set the logging function

SYNOPSIS

            #include <libpmem.h>
            typedef void pmem_log_function(
                enum pmem_log_level level,
                const char *file_name,
                unsigned line_no,
                const char *function_name,
                const char *message);
            int pmem_log_set_function(pmem_log_function *log_function);

DESCRIPTION
pmem_log_set_function() allows choosing the function which will get all the generated logging messages. The log_function can be either PMEM_LOG_USE_DEFAULT_FUNCTION which will use the default logging function (built into the library) or a pointer to a user-defined function.

The parameters of a user-defined log function are as follows:

•   level - the log level of the message (see pmem_log_set_threshold(3) for available log levels)

•   file_name - name of the source file where the message is coming from. It could be set to NULL and in such case, neither line_no nor function_name are provided.

•   line_no - the source file line where the message is coming from

•   function_name - the function name where the message is coming from

•   message - the message string

THE DEFAULT LOGGING FUNCTION
The library provides the default logging function which writes messages to syslog(3) and to stderr(3). This function is enabled during library initialization and can be restored using PMEM_LOG_USE_DEFAULT_FUNCTION value as the log_function argument.

The default logging function sinks all the logging messages into syslog(3) unconditionally. Additionally, it sinks a logging message into stderr(3) if its logging level is not less severe than indicated by the PMEM_LOG_THRESHOLD_AUX threshold’s value and it is not of level PMEM_LOG_LEVEL_HARK.

Note that the PMEM_LOG_THRESHOLD threshold’s value applies to the default logging function. Please see the notes below.

RETURN VALUE
pmem_log_set_function() function returns 0 on success or returns a non-zero value and sets errno on failure. On failure, the logging function remains unchanged.

ERRORS
pmem_log_set_function() can set the following errno values on fail:

•   EAGAIN - multiple threads attempted to change the logging function concurrently. A retry may fix the problem. This error is not expected when the function is called from just one thread at a time.

NOTE
The logging messages of level less severe than indicated by the PMEM_LOG_THRESHOLD threshold’s value won’t make it to the logging function no matter whether the logging function is the default logging function or user-provided.

The user-defined function must be thread-safe.

The library will call user defined function before returning from pmem_log_set_function() to deliver basic information about the library:

•   “src version: 2.y.z”

•   “compiled with support for shutdown state”

•   “compiled with libndctl 63+”

SEE ALSO
pmem_log_get_threshold(3), pmem_log_set_threshold(3).