illumos: manual page: log.4d

LOG(4D) LOG(4D)

NAME

log - interface to STREAMS error logging and event tracing

SYNOPSIS

#include <sys/strlog.h>

#include <sys/log.h>

DESCRIPTION

log is a STREAMS software device driver that provides an interface for
console logging and for the STREAMS error logging and event tracing
processes (see strerr(8), and strace(8)). log presents two separate
interfaces: a function call interface in the kernel through which STREAMS
drivers and modules submit log messages; and a set of ioctl(2) requests
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

log messages are generated within the kernel by calls to the function
strlog():

strlog(short mid,
short sid,
char level,
ushort_t 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(3C) style format string, except that %s, %e, %E, %g, and %G
conversion specifications are not handled. Up to NLOGARGS (in this
release, three) numeric or character arguments can be provided.

User Interface

log is implemented as a cloneable device, it clones itself without
intervention from the system clone device. 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 using 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.

struct trace_ids {
short ti_mid;
short ti_sid;
char ti_level;
};

Each trace_ids structure specifies a mid, sid, and level from which
messages will be accepted. strlog(9F) 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 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 using the ioctl call, log
will begin sending up messages subject to the restrictions noted above.
These messages are obtained using the getmsg(2) function. 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.

struct log_ctl {
short mid;
short sid;
char level; /* level of message for tracing */
short flags; /* message disposition */
#if defined(_LP64) || defined(_I32LPx)
clock32_t ltime; /* time in machine ticks since boot */
time32_t ttime; /* time in seconds since 1970 */
#else
clock_t ltime;
time_t ttime;
#endif
int seq_no; /* sequence number */
int pri; /* priority = (facility|level) */
};

The priority consists 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 string.

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, 32-bits each, on the next 32-bit boundary
following the end of the format string.

ENXIO is returned for I_TRCLOG ioctls without any trace_ids structures,
or for any unrecognized ioctl calls. The driver silently ignores
incorrectly formatted log messages sent to the driver by a user process
(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).

Driver Configuration

The following driver configuration properties may be defined in the
log.conf file.

msgid=1
If msgid=1, each message will be preceded by a message ID as
described in syslogd(8).

msgid=0
If msgid=0, message IDs will not be generated. This property
is unstable and may be removed in a future release.

EXAMPLES

Example 1 I_ERRLOG registration.

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 2 I_TRCLOG registration.

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

/dev/log
Log driver.

/dev/conslog
Write only instance of the log driver, for
console logging.

/kernel/drv/log.conf
Log configuration file.