path: root/man3/fmtmsg.3

.\"  Copyright 2002 walter harms (walter.harms@informatik.uni-oldenburg.de)
.\"  Distributed under GPL
.\"  adapted glibc info page
.\"  
.\"  This should run as 'Guru Meditation' (amiga joke :)
.\"  The function is quite complex an deserves an example
.\"
.\"  Polished, aeb, 2003-11-01
.TH fmtmsg 3 2003-11-01 "" "Linux Programmer's Manual"
.SH NAME
fmtmsg \- print formatted error messages
.SH SYNOPSIS
.nf
.sp
.B #include <fmtmsg.h>
.sp
.BI "int fmtmsg(long " classification ", const char *" label ,
.br
.BI "           int " severity ", const char *" text ,
.br
.BI "           const char *" action ", const char *" tag );
.sp
.fi
.SH DESCRIPTION
This function displays a message described by its parameters on the device(s)
specified in the
.I classification
parameter. For messages written to
.IR stderr ,
the format depends on the
.B MSGVERB
environment variable.
.LP
The
.I label
parameter 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.  
.LP
The
.I text
parameter describes the condition of the error.
.LP
The
.I action
parameter describes possible steps to recover from the error.
If it is printed, it is prefixed by "TO FIX: ".
.LP
The
.I tag
parameter is a reference to the online documentation where more
information can be found.  It should contain the
.I label
value and a unique identification number.
.SS "Dummy parameters"
Each of the parameters can have a dummy value. The dummy classification value
.B MM_NULLMC
(0L) does not specify any output, so nothing is printed.
The dummy severity value
.B NO_SEV
(0) says that no severity is supplied.
The values
.BR MM_NULLLBL ,
.BR MM_NULLTXT ,
.BR MM_NULLACT ,
.BR MM_NULLTAG
are synonyms for ((char *) 0), the empty string, and
.B MM_NULLSEV
is a synonym for
.BR NO_SEV .
.SS "The classification parameter"
The 
.I classification 
parameter is the sum of values describing 4 types of information.
.br 
.sp
The first value defines the output channel.
.TP 12n
.B MM_PRINT
Output to
.IR stderr .
.TP
.B MM_CONSOLE
Output to the system console.
.TP
.B "MM_PRINT | MM_CONSOLE"
Output to both.
.PP
The second value is the source of the error:
.TP 12n
.B MM_HARD
A hardware error occurred.
.TP
.B MM_FIRM
A firmware error occurred.
.TP
.B MM_SOFT
A software error occurred.
.PP
The third value encodes the detector of the problem:
.TP 12n
.B MM_APPL
It is detected by an application.
.TP
.B MM_UTIL
It is detected by a utility.
.TP
.B MM_OPSYS
It is detected by the operating system.
.PP
The fourth value shows the severity of the incident:
.TP 12n
.B MM_RECOVER
It is a recoverable error.
.TP
.B MM_NRECOV
It is a non-recoverable error.
.SS "The severity parameter"
The 
.I severity 
parameter can take one of the following values:
.TP 12n
.B MM_NOSEV
No severity is printed.
.TP
.B MM_HALT
This value is printed as HALT.
.TP
.B MM_ERROR
This value is printed as ERROR.
.TP
.B MM_WARNING
This value is printed as WARNING.
.TP
.B MM_INFO
This value is printed as INFO.
.PP
The numeric values are between 0 and 4. Using 
.B addseverity()
or the environment variable
.B SEV_LEVEL
you can add more levels and strings to print.
.SH ENVIRONMENT
The environment variable 
.B MSGVERB
("message verbosity") can be used to suppress parts of
the output to
.IR stderr .
(It does not influence output to the console.)
When this variable is defined, is non-NULL, and is a colon-separated
list of valid keywords, then only the parts of the message corresponding
to these keywords is printed.
Valid keywords are "label", "severity", "text", "action" and "tag".
.PP
The environment variable
.B SEV_LEVEL
can be used to introduce new severity levels.
By default, only the five severity levels described
above are available.  Any other numeric value would make fmtmsg() print
nothing.
If the user puts 
.B SEV_LEVEL
with a format like
.sp
.RS
SEV_LEVEL=[description[:description[:...]]]
.RE
.sp
in the environment of the process before the first call to fmtmsg(),
where each description is of the form
.sp
.RS
severity-keyword,level,printstring
.RE
.sp
then
.I fmtmsg()
will also accept the indicated values for the level (in addition to
the standard levels 0-4), and use the indicated printstring when
such a level occurs.
.LP
The severity-keyword part is not used by
.I fmtmsg()
but it has to be present.  
The level part is a string representation of a number.  
The numeric value must be a number greater than 4.
This value must be used in the severity parameter of 
.I fmtmsg()
to select this class.  It is not possible to overwrite
any of the predefined classes.  The printstring
is the string printed when a message of this class is processed by
.IR fmtmsg() .
.SH "RETURN VALUES"
The function can return 4 values:
.TP 12n
.B MM_OK
Everything went smooth.
.TP
.B MM_NOTOK
Complete failure.
.TP
.B MM_NOMSG
Error writing to
.IR stderr .
.TP
.B MM_NOCON
Error writing to the console.
.SH "CONFORMING TO"
The functions
.I fmtmsg()
and
.IR addseverity() ,
and environment variables
.B MSGVERB
and
.B SEV_LEVEL
come from System V (XPG4-UNIX).
The function
.I fmtmsg()
and the environment variable
.B MSGVERB
are described in POSIX 1003.1-2001.
.SH NOTES
System V and Unixware man pages tell us that these functions
have been replaced by "pfmt() and addsev()" or by "pfmt(),
vpfmt(), lfmt(), and vlfmt()", and will be removed later.
.SH EXAMPLE
.nf
#include <stdio.h>
#include <fmtmsg.h>

int main() {
  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\en");
      break;
    case MM_NOMSG:
      printf("Nothing printed to stderr\en");
      break;
    case MM_NOCON:
      printf("No console output\en");
      break;
    default:
      printf("Unknown error from fmtmsg()\en");
  }
  return 0;
}
.fi
.PP
The output should be:
.nf
  util-linux:mount: ERROR: unknown mount option
  TO FIX: See mount(8).  util-linux:mount:017
.fi
and after
.nf
  MSGVERB=text:action; export MSGVERB
.fi
the output becomes:
.nf
  unknown mount option
  TO FIX: See mount(8).
.fi
.SH "SEE ALSO"
.BR addseverity (3),
.BR perror (3)