fmtmsg - print formatted error messages

#include <fmtmsg.h>
int fmtmsg(long classification, const char *label,
 int severity, const char *text,
 const char *action, const char *tag);

This function displays a message described by its arguments on the device(s) specified in the classification argument. For messages written to stderr, the format depends on the MSGVERB environment variable.

The label argument identifies the source of the message. The string must consist of two colon separated parts where the first part has not more than 10 and the second part not more than 14 characters.

The text argument describes the condition of the error.

The action argument describes possible steps to recover from the error. If it is printed, it is prefixed by "TO FIX: ".

The tag argument is a reference to the online documentation where more information can be found. It should contain the label value and a unique identification number.

Dummy arguments

Each of the arguments can have a dummy value. The dummy classification value MM_NULLMC (0L) does not specify any output, so nothing is printed. The dummy severity value NO_SEV (0) says that no severity is supplied. The values MM_NULLLBL, MM_NULLTXT, MM_NULLACT, MM_NULLTAG are synonyms for ((char *) 0), the empty string, and MM_NULLSEV is a synonym for NO_SEV.

The classification argument

The classification argument is the sum of values describing 4 types of information.

The first value defines the output channel.

MM_PRINT

Output to stderr.

MM_CONSOLE

Output to the system console.

MM_PRINT | MM_CONSOLE

Output to both.

The second value is the source of the error:

MM_HARD

A hardware error occurred.

MM_FIRM

A firmware error occurred.

MM_SOFT

A software error occurred.

The third value encodes the detector of the problem:

MM_APPL

It is detected by an application.

MM_UTIL

It is detected by a utility.

MM_OPSYS

It is detected by the operating system.

The fourth value shows the severity of the incident:

MM_RECOVER

It is a recoverable error.

MM_NRECOV

It is a nonrecoverable error.

The severity argument

The severity argument can take one of the following values:

MM_NOSEV

No severity is printed.

MM_HALT

This value is printed as HALT.

MM_ERROR

This value is printed as ERROR.

MM_WARNING

This value is printed as WARNING.

MM_INFO

This value is printed as INFO.

The numeric values are between 0 and 4. Using addseverity(3) or the environment variable SEV_LEVEL you can add more levels and strings to print.

The function can return 4 values:

MM_OK

Everything went smooth.

MM_NOTOK

Complete failure.

MM_NOMSG

Error writing to stderr.

MM_NOCON

Error writing to the console.

#include <fmtmsg.h>
#include <stdio.h>
#include <stdlib.h>
int
main(void)
{
    long class = MM_PRINT | MM_SOFT | MM_OPSYS | MM_RECOVER;
    int err;
    err = fmtmsg(class, "util-linux:mount", MM_ERROR,
                 "unknown mount option", "See mount(8).",
                 "util-linux:mount:017");
    switch (err) {
    case MM_OK:
        break;
    case MM_NOTOK:
        printf("Nothing printed\n");
        break;
    case MM_NOMSG:
        printf("Nothing printed to stderr\n");
        break;
    case MM_NOCON:
        printf("No console output\n");
        break;
    default:
        printf("Unknown error from fmtmsg()\n");
    }
    exit(EXIT_SUCCESS);
}

The output should be:

util-linux:mount: ERROR: unknown mount option
TO FIX: See mount(8).  util-linux:mount:017

and after

MSGVERB=text:action; export MSGVERB

the output becomes:

unknown mount option
TO FIX: See mount(8).

addseverity(3), perror(3)