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.\" Copyright (c) 2002 Mike Barcroft <mike@FreeBSD.org>
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.\" $FreeBSD: src/lib/libc/gen/fmtmsg.3,v 1.4 2002/12/04 18:57:44 ru Exp $
.\" $DragonFly: src/lib/libc/gen/fmtmsg.3,v 1.1 2008/10/06 21:01:37 swildner Exp $
.\"
.Dd October 6, 2008
.Dt FMTMSG 3
.Os
.Sh NAME
.Nm fmtmsg
.Nd display a detailed diagnostic message
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In fmtmsg.h
.Ft int
.Fo fmtmsg
.Fa "long classification" "const char *label" "int severity"
.Fa "const char *text" "const char *action" "const char *tag"
.Fc
.Sh DESCRIPTION
The
.Fn fmtmsg
function displays a detailed diagnostic message, based on
the supplied arguments, to
.Dv stderr
and/or the system console.
.Pp
The
.Fa classification
argument is the bitwise inclusive
.Tn OR
of zero or one of the manifest constants from
each of the classification groups below.
The Output classification group is an exception since both
.Dv MM_PRINT
and
.Dv MM_CONSOLE
may be specified.
.Bl -tag -width indent
.It Output
.Bl -tag -width ".Dv MM_CONSOLE"
.It Dv MM_PRINT
Output should take place on
.Dv stderr .
.It Dv MM_CONSOLE
Output should take place on the system console.
.El
.It "Source of Condition (Major)"
.Bl -tag -width ".Dv MM_CONSOLE"
.It Dv MM_HARD
The source of the condition is hardware related.
.It Dv MM_SOFT
The source of the condition is software related.
.It Dv MM_FIRM
The source of the condition is firmware related.
.El
.It "Source of Condition (Minor)"
.Bl -tag -width ".Dv MM_CONSOLE"
.It Dv MM_APPL
The condition was detected at the application level.
.It Dv MM_UTIL
The condition was detected at the utility level.
.It Dv MM_OPSYS
The condition was detected at the operating system level.
.El
.It Status
.Bl -tag -width ".Dv MM_CONSOLE"
.It Dv MM_RECOVER
The application can recover from the condition.
.It Dv MM_NRECOV
The application is unable to recover from the condition.
.El
.El
.Pp
Alternatively, the
.Dv MM_NULLMC
manifest constant may be used to specify no classification.
.Pp
The
.Fa label
argument indicates the source of the message.
It is made up of two fields separated by a colon
.Pq Ql \&: .
The first field can be up to 10 bytes,
and the second field can be up to 14 bytes.
The
.Dv MM_NULLLBL
manifest constant may be used to specify no label.
.Pp
The
.Fa severity
argument identifies the importance of the condition.
One of the following manifest constants should be used for this argument.
.Bl -tag -offset indent -width ".Dv MM_WARNING"
.It Dv MM_HALT
The application has confronted a serious fault and is halting.
.It Dv MM_ERROR
The application has detected a fault.
.It Dv MM_WARNING
The application has detected an unusual condition,
that could be indicative of a problem.
.It Dv MM_INFO
The application is providing information about a non-error condition.
.It Dv MM_NOSEV
No severity level supplied.
.El
.Pp
The
.Fa text
argument details the error condition that caused the message.
There is no limit on the size of this character string.
The
.Dv MM_NULLTXT
manifest constant may be used to specify no text.
.Pp
The
.Fa action
argument details how the error-recovery process should begin.
Upon output,
.Fn fmtmsg
will prefix
.Qq Li "TO FIX:"
to the beginning of the
.Fa action
argument.
The
.Dv MM_NULLACT
manifest constant may be used to specify no action.
.Pp
The
.Fa tag
argument should reference online documentation for the message.
This usually includes the
.Fa label
and a unique identifying number.
An example tag is
.Qq Li BSD:ls:168 .
The
.Dv MM_NULLTAG
manifest constant may be used to specify no tag.
.Sh RETURN VALUES
The
.Fn fmtmsg
function returns
.Dv MM_OK
upon success,
.Dv MM_NOMSG
to indicate output to
.Dv stderr
failed,
.Dv MM_NOCON
to indicate output to the system console failed, or
.Dv MM_NOTOK
to indicate output to
.Dv stderr
and the system console failed.
.Sh ENVIRONMENT
The
.Ev MSGVERB
(message verbosity)
environment variable specifies which arguments to
.Fn fmtmsg
will be output to
.Dv stderr ,
and in which order.
.Ev MSGVERB
should be a colon
.Pq Ql \&:
separated list of identifiers.
Valid identifiers include:
.Li label , severity , text , action ,
and
.Li tag .
If invalid identifiers are specified or incorrectly separated,
the default message verbosity and ordering will be used.
The default ordering is equivalent to a
.Ev MSGVERB
with a value of
.Qq Li label:severity:text:action:tag .
.Sh EXAMPLES
The code:
.Bd -literal -offset indent
fmtmsg(MM_UTIL | MM_PRINT, "BSD:ls", MM_ERROR,
    "illegal option -- z", "refer to manual", "BSD:ls:001");
.Ed
.Pp
will output:
.Bd -literal -offset indent
BSD:ls: ERROR: illegal option -- z
TO FIX: refer to manual BSD:ls:001
.Ed
.Pp
to
.Dv stderr .
.Pp
The same code, with
.Ev MSGVERB
set to
.Qq Li "text:severity:action:tag" ,
produces:
.Bd -literal -offset indent
illegal option -- z: ERROR
TO FIX: refer to manual BSD:ls:001
.Ed
.Sh SEE ALSO
.Xr err 3 ,
.Xr exit 3 ,
.Xr strerror 3
.Sh STANDARDS
The
.Fn fmtmsg
function conforms to
.St -p1003.1-2001 .
.Sh HISTORY
The
.Fn fmtmsg
function first appeared in
.Fx 5.0 .
It was imported into
.Dx 2.1 .
.Sh BUGS
Specifying
.Dv MM_NULLMC
for the
.Fa classification
argument makes little sense, since without an output specified,
.Fn fmtmsg
is unable to do anything useful.
.Pp
In order for
.Fn fmtmsg
to output to the system console, the effective
user must have appropriate permission to write to
.Pa /dev/console .
This means that on most systems
.Fn fmtmsg
will return
.Dv MM_NOCON
unless the effective user is root.