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log(7)									log(7)

NAME    [Toc]    [Back]

     log - interface to	STREAMS	error logging and event	tracing

DESCRIPTION    [Toc]    [Back]

     log is a STREAMS software device driver that provides an interface	for
     console logging and for the STREAMS error logging and event tracing
     processes [strerr(1M), strace(1M)].  log presents two separate
     interfaces: a function call interface in the kernel through which STREAMS
     drivers and modules submit	log messages; and a subset of ioctl(2) system
     calls and STREAMS messages	for interaction	with a user level console
     logger, an	error logger, a	trace logger, or processes that	need to	submit
     their own log messages.

   Kernel Interface    [Toc]    [Back]
     log messages are generated	within the kernel by calls to the function

	  strlog(mid, sid, level, flags, fmt, arg1, ...)
	  short	mid, sid;
	  char level;
	  ushort flags;
	  char *fmt;
	  unsigned arg1;

     Required definitions are contained	in <sys/strlog.h>, <sys/log.h>,	and
     <sys/syslog.h>.  mid is the STREAMS module	id number for the module or
     driver submitting the log message.	 sid is	an internal sub-id number
     usually used to identify a	particular minor device	of a driver.  level is
     a tracing level that allows for selective screening out of	low priority
     messages from the tracer.	flags are any combination of SL_ERROR (the
     message is	for the	error logger), SL_TRACE	(the message is	for the
     tracer), SL_CONSOLE (the message is for the console logger), SL_FATAL
     (advisory notification of a fatal error), and SL_NOTIFY (request that a
     copy of the message be mailed to the system administrator).  fmt is a
     printf(3S)	style format string, except that %s, %e, %E, %g, and %G
     conversion	specifications are not handled.	 Up to NLOGARGS	(currently 3)
     numeric or	character arguments can	be provided.

   User	Interface
     log is opened via the clone interface, /dev/log.  Each open of /dev/log
     obtains a separate	stream to log.	In order to receive log	messages, a
     process must first	notify log whether it is an error logger, trace
     logger, or	console	logger via a STREAMS I_STR ioctl call (see below).
     For the console logger, the I_STR ioctl has an ic_cmd field of I_CONSLOG,
     with no accompanying data.	 For the error logger, the I_STR ioctl has an
     ic_cmd field of I_ERRLOG, with no accompanying data.  For the trace
     logger, the ioctl has an ic_cmd field of I_TRCLOG,	and must be
     accompanied by a data buffer containing an	array of one or	more struct
     trace_ids elements.  Each trace_ids structure specifies an	mid, sid, and
     level from	which message will be accepted.	 strlog	will accept messages
     whose mid and sid exactly match those in the trace_ids structure, and
     whose level is less than or equal to the level given in the trace_ids

									Page 1

log(7)									log(7)

     structure.	 A value of -1 in any of the fields of the trace_ids structure
     indicates that any	value is accepted for that field.

     Once the logger process has identified itself via the ioctl call, log
     will begin	sending	up messages subject to the restrictions	noted above.
     These messages are	obtained via the getmsg(2) system call.	 The control
     part of this message contains a log_ctl structure,	which specifies	the
     mid, sid, level, flags, time in ticks since boot that the message was
     submitted,	the corresponding time in seconds since	Jan. 1,	1970, a
     sequence number, and a priority.  The time	in seconds since 1970 is
     provided so that the date and time	of the message can be easily computed,
     and the time in ticks since boot is provided so that the relative timing
     of	log messages can be determined.

     The priority is comprised of a priority code and a	facility code, found
     in	<sys/syslog.h>.	 If SL_CONSOLE is set in flags,	the priority code is
     set as follows. If	SL_WARN	is set,	the priority code is set to
     LOG_WARNING.  If SL_FATAL is set, the priority code is set	to LOG_CRIT.
     If	SL_ERROR is set, the priority code is set to LOG_ERR.  If SL_NOTE is
     set, the priority code is set to LOG_NOTICE.  If SL_TRACE is set, the
     priority code is set to LOG_DEBUG.	 If only SL_CONSOLE is set, the
     priority code is set to LOG_INFO. Messages	originating from the kernel
     have the facility code set	to LOG_KERN. Most messages originating from
     user processes will have the facility code	set to LOG_USER.

     Different sequence	numbers	are maintained for the error and trace logging
     streams, and are provided so that gaps in the sequence of messages	can be
     determined	(during	times of high message traffic some messages may	not be
     delivered by the logger to	avoid hogging system resources).  The data
     part of the message contains the unexpanded text of the format string
     (null terminated),	followed by NLOGARGS words for the arguments to	the
     format string, aligned on the first word boundary following the format

     A process may also	send a message of the same structure to	log, even if
     it	is not an error	or trace logger.  The only fields of the log_ctl
     structure in the control part of the message that are accepted are	the
     level, flags, and pri fields; all other fields are	filled in by log
     before being forwarded to the appropriate logger.	The data portion must
     contain a null terminated format string, and any arguments	(up to
     NLOGARGS) must be packed one word each, on	the next word boundary
     following the end of the format string.

     ENXIO is returned for I_TRCLOG ioctls without any trace_ids structures,
     or	for any	unrecognized I_STR ioctl calls.	 Incorrectly formatted log
     messages sent to the driver by a user process are silently	ignored	(no
     error results).

     Processes that wish to write a message to the console logger may direct
     their output to /dev/conslog, using either	write(2) or putmsg(2).

									Page 2

log(7)									log(7)

EXAMPLES    [Toc]    [Back]

     Example of	I_ERRLOG notification.

	  struct strioctl ioc;

	  ioc.ic_cmd = I_ERRLOG;
	  ioc.ic_timout	= 0;  /* default timeout (15 secs.) */
	  ioc.ic_len = 0;
	  ioc.ic_dp = NULL;
	  ioctl(log, I_STR, &ioc);

     Example of	I_TRCLOG notification.

	  struct trace_ids tid[2];

	  tid[0].ti_mid	= 2;
	  tid[0].ti_sid	= 0;
	  tid[0].ti_level = 1;
	  tid[1].ti_mid	= 1002;
	  tid[1].ti_sid	= -1; /* any sub-id will be allowed */
	  tid[1].ti_level = -1;	   /* any level	will be	allowed	*/

	  ioc.ic_cmd = I_TRCLOG;
	  ioc.ic_timout	= 0;
	  ioc.ic_len = 2 * sizeof(struct trace_ids);
	  ioc.ic_dp = (char *)tid;
	  ioctl(log, I_STR, &ioc);

     Example of	submitting a log message (no arguments).

	  struct strbuf	ctl, dat;
	  struct log_ctl lc;
	  char *message	= "Don't forget	to pick	up some	milk
			   on the way home";

	  ctl.len = ctl.maxlen = sizeof(lc);
	  ctl.buf = (char *)&lc;
	  dat.len = dat.maxlen = strlen(message);
	  dat.buf = message;

	  lc.level = 0;
	  lc.flags = SL_ERROR|SL_NOTIFY;
	  putmsg(log, &ctl, &dat, 0);

FILES    [Toc]    [Back]


									Page 3

log(7)									log(7)

SEE ALSO    [Toc]    [Back]

     strace(1M), strerr(1M), getmsg(2),	intro(2), putmsg(2), write(2),

NOTES    [Toc]    [Back]

     The log driver high and low water marks are tunable via the master	file.

									PPPPaaaaggggeeee 4444
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