logsys_overview(8) Logsys Library Overview


The logsys library provides a generically usable logging and tracing system for use by applications. It supports many features including:

Configurable subsystem logging or single system logging

Threaded non-blocking logging of log output data for better non-blocking performance

Support for 8 tracing levels and tracing the entering and leaving of functions

Declaration of logging system or subsystem without calling any functions

Dynamic reconfiguration of the logging system parameters

Logging to syslog, file, stderr.

Declaration of the System logger

The logsys library is initially configured by including logsys.h and declaring a logger. Once the logger is declared, optional subsystem loggers can be declared in every file.

The definition LOGSYS_DECLARE_SYSTEM is placed after the include section of one C file in the application. This declaration creates a constructor function which will be called automatically before main() is executed. This technique avoids the need for calling any setup functions in short applications that don't require it and enables full logging capabilities before any application code is executed.

#define LOGSYS_DECLARE_SYSTEM (name, mode, debug, file, file_priority, syslog_facility, syslog_priority, format, fltsize)

The name parameter is the name of the application or system.

The mode parameter is the logging mode of the system. The following modes can be configured by logically ORing these flags:

LOGSYS_MODE_OUTPUT_FILE: Output all log data to the file parameter of this declaration

LOGSYS_MODE_OUTPUT_STDERR: Output all log data to the stderr descriptor

LOGSYS_MODE_OUTPUT_SYSLOG: Output all log data to syslog using a non-blocking thread

LOGSYS_MODE_FORK: This flags tells logsys to queue all data untill the application has forked. The application is then responsible to call logsys_fork_completed to flush the queue and start logging.

LOGSYS_MODE_THREADED: Starts a separate thread to handle non-blocking logging operations. If this flag is not specified, the logging operations are blocking.

The debug parameter, if enabled, turns off all messages priority filtering, recording everything everywhere.

The file parameter specifies the filename that should be used to log messages. This parameter may be NULL and no log file will be created.

The file_priority parameter specifies the message priority that should be logged to file.

The syslog_facility parameter is the syslog facility that should be used when logging messages.

The syslog_priority, similar to file_priority, specifies the message priority that should be logged to syslog.

The format parameter allows to set custom output format. Set to NULL to use built-in default.

The fltsize parameter specifies the flight recorder buffer size in bytes. The requested value is increased by the size of 2 unsigned ints and rounded to the next PAGE_SIZE.

An example declaration would be:

#include <corosync/logsys.h>

LOGSYS_DECLARE_SYSTEM ("test", /* name */
        0,                                                /* debug */
        NULL,                                             /* logfile path */
        LOGSYS_LEVEL_INFO,                                /* logfile_priority */
        LOG_DAEMON,                                       /* syslog facility */
        LOGSYS_LEVEL_INFO,                                /* syslog level */
        NULL,                                             /* use default format */
        1000000);                                         /* flight recorder size */

Declaration of subsystems

The logsys library supports the logging of information to one main system or subsystem. This is specified in each individual object C file in the system and it is entirely optional.

An example:


It is possible to use the same subsystem name in separate object files. In this case, the individual logging parameters for those subsystem identifier will be used.

A newly created subsystem inherits the system configuration at the time of creation.

It is possible to override every configuration option on a subsystem base throught the configuration API.

Logging Messages

The definition log_printf is used to log information to the log. It works in a similiar fashion to printf, except it has a first parameter of level which may be the following: LOGSYS_LEVEL_EMERG LOGSYS_LEVEL_ALERT LOGSYS_LEVEL_CRIT LOGSYS_LEVEL_ERR LOGSYS_LEVEL_WARNING LOGSYS_LEVEL_NOTICE LOGSYS_LEVEL_INFO LOGSYS_LEVEL_DEBUG

An example of using log_printf would be

log_printf (LOGSYS_LEVEL_EMERG, "This is an emergency %s value %d, string, value);

Tracing of functions can be done using ENTER(), LEAVE();

An example of using ENTER is void function (char *name) { ENTER(); LEAVE(); }

Individual tracing levels are supported through the macros TRACE1(format, args) TRACE2(format, args) TRACE8(format, args)

An example of using TRACE is

char *name = "test"; TRACE7 ("This is a trace 7 log with name %s, name);

Note that ENTER/LEAVE/TRACE* calls are recorded only in the flight recorder.