strlog(7) Miscellaneous Information Manual strlog(7)
strlog, log - STREAMS log driver driver
int strlog( short mid, short sid, char level, ushort flags char fmt,
Specifies the STREAMS module ID number for the driver or module submitting the log message. Specifies the sub-ID number of a minor device
associated with the STREAMS module or driver identified by mid. Specifies a level for screening lower-level event messages from a tracer.
Contains several flags that can be set in various combinations. The flags are as follows: The message is for the error logger. The mes-
sage is for the tracer. The message is for the console logger. Provides a notification of a fatal error. Makes a request to mail a copy
of a message to the system administrator.
The following are additional flags. The strlog interface does not use these flags: The message is a warning. The message is a note. A
printf style format string. This accepts the %x, %l, %o, %u, %d, %c, and %s conversion specifications. Numeric or character arguments for
process-specific information. There is no maximum number of arguments that can be specified.
The STREAMS log driver allows user-level processes, and STREAMS drivers and modules, to perform error logging and event tracing. This is
done via a user interface and a kernel interface.
The interface that this driver presents to user-level processes is a subset of the ioctl() system calls and STREAMS message formats. These
processes can be error loggers, trace loggers, or other user processes, that generate error or event messages. The user interface collects
log messages from the log driver, and also generates log messages from user processes.
The driver also accepts log messages from STREAMS drivers and modules in the kernel via its function call interface. The kernel interface
enters requests or calls from STREAMS drivers and modules into log messages.
STREAMS drivers and modules generate log messages by calls to the strlog() function. Definitions used in these calls are contained in the
log_ctl structure in the </sys/strlog.h> header file. The SYNOPSIS section describes the kernel interface.
User processes access the log driver with an open() call to /dev/streams/log. Each open to the device will obtain a separate stream.
After a process opens /dev/streams/log, it indicates whether it is an error logger or trace logger. It does this by issuing an I_STR
ioctl() system call containing the appropriate data and control information in a trace_ids structure. For an error logger, the I_STR
ioctl() contains an ic_cmd field of I_ERRLOG with no data. For a trace logger, the I_STR ioctl() contains an ic_cmd field of I_TRCLOG and
a data buffer consisting of an array of one or more trace_ids structures.
If any of the fields of the trace_ids structure contain a value of -1, /dev/streams/log will accept whatever value it receives in that
field. Otherwise, strlog only accepts messages only if the values of mid and sid are the same as their counterparts in the trace_ids
structure, and if the message's level is equal to or less than the level value in the trace_ids structure.
Once the logger process has sent the I_STR ioctl() call, the STREAMS log driver begins to send log messages matching the restrictions to
the logger process. The logger process obtains the log messages via the getmsg(2) system call. The control part of the messages passed in
this call includes a log_ctl structure, which indicates the mid, sid and level, time in ticks since the boot time that the message was sub-
mitted, the corresponding time in seconds since January 1, 1970, and a sequence number. The time in seconds since January 1, 1970 is pro-
vided so that the date and time of the message can be easily computed. The time in ticks since boot time is provided so that the relative
timing of log messages can be determined. In addition to the information contained in the log_ctl structure, there is also a priority
The priority indication consists of a priority code and a facility code (found in /sys/syslog.h). The valid values for priority codes are
the following, based on the setting(s) in flags: If SL_CONSOLE is set in flags. If SL_CONSOLE and SL_WARN are set in flags. If SL_CONSOLE
and SL_FATAL are set in flags. If SL_CONSOLE and SL_ERROR are set in flags. If SL_CONSOLE and SL_NOTE are set in flags. If SL_CONSOLE
and SL_TRACE are set in flags.
The valid values for facility codes are the following: If the message originates from the kernel. If the message originates from a user
process. However, these processes may sometimes set another facility code value instead.
A user process, other than an error or trace logger, can send a log message to strlog(). The driver will accept only the flags and level
fields of the log_ctl structure in the control part of the message, and a properly formatted data part of the message. The data part of
the message is properly formatted if it contains a null-terminated format string, followed by any arguments packed one word each after the
end of the string.
A different series of sequence numbers is provided for error and trace logging streams. These sequence numbers are intended to help track
the delivery of the messages. A gap in a sequence of numbers indicates that the logger process did not successfully deliver them. This can
happen if the logger process stops sending messages for one reason or another (see the strace and strerr command reference pages for more
information). The data part of messages contains unexpanded text of the format string (null terminated), followed by any arguments packed
one word each after the end of the string.
The following examples illustrate how to use the strlog interface for some basic uses. This code example segment illustrates how a STREAMS
module can generate a console log message: strlog(TMUX,minor(mydev),0,SL_CONSOLE|SL_FATAL,
"TMUX driver (minor:%d) suffers resource shortage.",
minor(mydev)); This code example illustrates how a user process can register itself with the STREAMS log driver using the ioctl()
command, I_ERRLOG. struct strioctl iocerr:
iocerr.ic_cmd = I_ERRLOG; iocerr.ic_timout = 0; iocerr.ic_len = 0; iocerr.ic_dp = NULL; ioctl(logfd, I_STR, &iocerr)
Tru64 UNIX does not provide a console logger. Note, however, that other systems may provide console loggers.
Specifies the clone interface. Specifies the header file for STREAMS logging. Specifies the header file for STREAMS options and ioctl()
If any of the following conditions occurs, strlog() driver's ioctl() command sets errno to the corresponding value: The I_TRCLOG ioctl()
call did not contain any trace_ids structures. The I_STR ioctl() call could not be recognized.
The driver does not return any errors for incorrectly formatted messages that user processes send.
Commands: strace(8), strerr(8).
Interfaces clone(7), streamio(7).
Functions: getmsg(2), putmsg(2), write(2). delim off