strlog(7)

NAME

strlog − STREAMS log driver

DESCRIPTION

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(2) 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.

Kernel Interface

STREAMS drivers and modules generate log messages by calls to the strlog function.

#include <sys/strlog.h>
int strlog(mid, sid, level, flags, fmt [,value]...);
short mid;
short sid;
char level;
ushort flags;
char *fmt;
int value;

mid specifies the STREAMS module ID number for the driver or module submitting the log message. sid specifies the sub-ID number of a minor device associated with the STREAMS module or driver identified by mid. level specifies a level for screening lower-level event messages from a tracer. flags contains several flags that can be set in various combinations. The flags are as follows:

SL_ERROR The message is for the error logger.

SL_TRACE The message is for the tracer.

SL_CONSOLE The message will be printed to the console.

SL_FATAL Provides a notification of a fatal error.

SL_NOTIFY 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:

SL_WARN The message is a warning.

SL_NOTE The message is a note.

fmt is a printf style format string. This accepts the %x, %l, %o, %u, %d, %c, and %s conversion specifications. values are numeric or character arguments for the format string. There is no maximum number of arguments that can be specified.

User Interface

User processes access the log driver with an open(2) call to /dev/strlog. Each open to the device will obtain a separate stream. After a process opens /dev/strlog, it indicates whether it is an error logger or trace logger. It does this by issuing an I_STR ioctl(2) system call with the appropriate value in the ic_cmd field of the strioctl structure, and the appropriate data and control information in a trace_ids structure:

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

The values for ic_cmd are:

I_ERRLOG Indicates an error logger. No trace_ids data is needed.

I_TRCLOG Indicates a trace logger. A data buffer consisting of an array of one or more trace_ids structures must be included.

If any of the fields of the trace_ids structure contain a value of -1, /dev/strlog 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(2) 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:

struct log_ctl {
        short   mid;
        short   sid;
        char    level;
        short   flags;
        long    ltime;
        long    ttime;
        int     seq_no;
};

The log_ctl structure indicates the mid, sid and level, time in ticks since the boot time that the message was submitted, the corresponding time in seconds since January 1, 1970, and a sequence number. The time in seconds since January 1, 1970 is provided 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.

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(1m) and strerr(1m) command reference pages for more information). The data part of messages contains text of the format string (null terminated), followed by any arguments.

EXAMPLES

The following examples illustrate how to use the strlog interface for some basic uses.

This code example segment illustrates how a STREAMS module can cause a message to be printed to the console:

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(2) command, I_ERRLOG.

struct strioctl iocerr:
int logfd;
if ((logfd = open("/dev/strlog", O_RDWR)) == -1) {
printf("Cannot open /dev/strlog\n");
exit(1);
}
iocerr.ic_cmd = I_ERRLOG;
iocerr.ic_timout = 0;
iocerr.ic_len = 0;
iocerr.ic_dp = NULL;
ioctl(logfd, I_STR, &iocerr);

This code is an example of a user-level process sending a message to the strlog driver.

struct strbuf control, data;
struct log_ctl log;
char *warning = "Fatal error for user level process";
int logfd;
if ((logfd = open("/dev/strlog", O_RDWR)) == -1) {
printf("Cannot open /dev/strlog\n");
exit(1);
}
control.len = control.maxlen = sizeof(log);
control.buf = (char *)&lc;
data.len = data.maxlen = strlen(warning);
data.buf = warning;
lc.level = 2;
lc.flags = SL_FATAL|SL_CONSOLE;
putmsg(logfd, &control, &data, 0);

ERRORS

If any of the following conditions occurs, strlog driver’s ioctl(2) command sets errno to the corresponding value:

[ENXIO] The I_TRCLOG ioctl(2) call did not contain any trace_ids structures.

[ENXIO] The I_STR ioctl(2) call could not be recognized.

The driver does not return any errors for incorrectly formatted messages that user processes send.

RETURN VALUES

Unless specified otherwise, upon successful completion, the strlog ioctl(2) commands return a value of 0 (zero). Otherwise, a value of -1 is returned.

FILES

/dev/strlog specifies the clone interface.
<sys/strlog.h> specifies the header file for streams logging. <stropts.h> specifies the header file for streams options and ioctl(2) commands.

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