.\"
.\" libexplain - Explain errno values returned by libc functions
.\" Copyright (C) 2013 Peter Miller
.\"
.\" This program is free software; you can redistribute it and/or modify it
.\" under the terms of the GNU General Public License as published by the
.\" Free Software Foundation; either version 3 of the License, or (at your
.\" option) any later version.
.\"
.\" This program is distributed in the hope that it will be useful, but
.\" WITHOUT ANY WARRANTY; without even the implied warranty of
.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
.\" General Public License for more details.
.\"
.\" You should have received a copy of the GNU General Public License along
.\" with this program. If not, see <http://www.gnu.org/licenses/>.
.\"
.ds n) explain_setpriority
.cp 0  \" Compatibility mode off.
.TH explain_setpriority 3
.SH NAME
explain_setpriority \- explain \f[I]setpriority\fP(2) errors
.if require_index \{
.XX "explain_setpriority(3)" "explain \f[I]setpriority\fP(2) errors"
.\}
.SH SYNOPSIS
#include <libexplain/setpriority.h>
.sp 0.3
.ad l
const char *explain_setpriority(int which, int who, int prio);
.br
const char *explain_errno_setpriority(int errnum, int which, int who, int
prio);
.br
void explain_message_setpriority(char *message, int message_size, int
which, int who, int prio);
.br
void explain_message_errno_setpriority(char *message, int message_size, int
errnum, int which, int who, int prio);
.ad b
.SH DESCRIPTION
These functions may be used to obtain explanations for errors returned by
the \f[I]setpriority\fP(2) system call.
.\" ----------------------------------------------------
.SS explain_setpriority
.ad l
const char *explain_setpriority(int which, int who, int prio);
.ad b
.PP
The \f[B]explain_setpriority\fP function is used to obtain an explanation
of an error returned by the \f[I]setpriority\fP(2) system call. The least
the message will contain is the value of \f[CW]strerror(errno)\fP, but
usually it will do much better, and indicate the underlying cause in more
detail.
.PP
The \f[I]errno\fP global variable will be used to obtain the error value to
be decoded.
.TP 8n
\f[I]which\fP
The original which, exactly as passed to the \f[I]setpriority\fP(2) system
call.
.TP 8n
\f[I]who\fP
The original who, exactly as passed to the \f[I]setpriority\fP(2) system
call.
.TP 8n
\f[I]prio\fP
The original prio, exactly as passed to the \f[I]setpriority\fP(2) system
call.
.TP 8n
Returns:
The message explaining the error. This message buffer is shared by all
libexplain functions which do not supply a buffer in their argument list.
This will be overwritten by the next call to any libexplain function which
shares this buffer, including other threads.
.PP
\f[B]Note:\fP This function is \f[B]not\fP thread safe, because it shares a
return buffer across all threads, and many other functions in this library.
.PP
\f[B]Example:\fP This function is intended to be used in a fashion similar
to the following example:
.RS
.ft CW
.fi
.ad l
if (setpriority(which, who, prio) < 0)
.ad b
.nf
{
.fi
.ad l
.in +4n
fprintf(stderr, "%s\en", explain_setpriority(which, who, prio));
.in -4n
.nf
    exit(EXIT_FAILURE);
}
.fi
.ft R
.ad b
.RE
.PP
The above code example is available pre\-packaged as the
\f[I]explain_setpriority_or_die\fP(3) function.
.\" ----------------------------------------------------
.SS explain_errno_setpriority
.ad l
const char *explain_errno_setpriority(int errnum, int which, int who, int
prio);
.ad b
.PP
The \f[B]explain_errno_setpriority\fP function is used to obtain an
explanation of an error returned by the \f[I]setpriority\fP(2) system call.
The least the message will contain is the value of
\f[CW]strerror(errno)\fP, but usually it will do much better, and indicate
the underlying cause in more detail.
.TP 8n
\f[I]errnum\fP
The error value to be decoded, usually obtained from the \f[I]errno\fP
global variable just before this function is called. This is necessary if
you need to call \f[B]any\fP code between the system call to be explained
and this function, because many libc functions will alter the value of
\f[I]errno\fP.
.TP 8n
\f[I]which\fP
The original which, exactly as passed to the \f[I]setpriority\fP(2) system
call.
.TP 8n
\f[I]who\fP
The original who, exactly as passed to the \f[I]setpriority\fP(2) system
call.
.TP 8n
\f[I]prio\fP
The original prio, exactly as passed to the \f[I]setpriority\fP(2) system
call.
.TP 8n
Returns:
The message explaining the error. This message buffer is shared by all
libexplain functions which do not supply a buffer in their argument list.
This will be overwritten by the next call to any libexplain function which
shares this buffer, including other threads.
.PP
\f[B]Note:\fP This function is \f[B]not\fP thread safe, because it shares a
return buffer across all threads, and many other functions in this library.
.PP
\f[B]Example:\fP This function is intended to be used in a fashion similar
to the following example:
.RS
.ft CW
.fi
.ad l
if (setpriority(which, who, prio) < 0)
.ad b
.nf
{
    int err = errno;
.fi
.ad l
.in +4n
fprintf(stderr, "%s\en", explain_errno_setpriority(err, which, who, prio));
.in -4n
.nf
    exit(EXIT_FAILURE);
}
.fi
.ft R
.ad b
.RE
.PP
The above code example is available pre\-packaged as the
\f[I]explain_setpriority_or_die\fP(3) function.
.\" ----------------------------------------------------
.SS explain_message_setpriority
.ad l
void explain_message_setpriority(char *message, int message_size, int
which, int who, int prio);
.ad b
.PP
The \f[B]explain_message_setpriority\fP function is used to obtain an
explanation of an error returned by the \f[I]setpriority\fP(2) system call.
The least the message will contain is the value of
\f[CW]strerror(errno)\fP, but usually it will do much better, and indicate
the underlying cause in more detail.
.PP
The \f[I]errno\fP global variable will be used to obtain the error value to
be decoded.
.TP 8n
\f[I]message\fP
The location in which to store the returned message. If a suitable message
return buffer is supplied, this function is thread safe.
.TP 8n
\f[I]message_size\fP
The size in bytes of the location in which to store the returned message.
.TP 8n
\f[I]which\fP
The original which, exactly as passed to the \f[I]setpriority\fP(2) system
call.
.TP 8n
\f[I]who\fP
The original who, exactly as passed to the \f[I]setpriority\fP(2) system
call.
.TP 8n
\f[I]prio\fP
The original prio, exactly as passed to the \f[I]setpriority\fP(2) system
call.
.PP
\f[B]Example:\fP This function is intended to be used in a fashion similar
to the following example:
.RS
.ft CW
.fi
.ad l
if (setpriority(which, who, prio) < 0)
.ad b
.nf
{
    char message[3000];
.in +4n
.fi
.ad l
explain_message_setpriority(message, sizeof(message), which, who, prio);
.nf
.in -4n
    fprintf(stderr, "%s\en", message);
    exit(EXIT_FAILURE);
}
.fi
.ft R
.ad b
.RE
.PP
The above code example is available pre\-packaged as the
\f[I]explain_setpriority_or_die\fP(3) function.
.\" ----------------------------------------------------
.SS explain_message_errno_setpriority
.ad l
void explain_message_errno_setpriority(char *message, int message_size, int
errnum, int which, int who, int prio);
.ad b
.PP
The \f[B]explain_message_errno_setpriority\fP function is used to obtain an
explanation of an error returned by the \f[I]setpriority\fP(2) system call.
The least the message will contain is the value of
\f[CW]strerror(errno)\fP, but usually it will do much better, and indicate
the underlying cause in more detail.
.TP 8n
\f[I]message\fP
The location in which to store the returned message. If a suitable message
return buffer is supplied, this function is thread safe.
.TP 8n
\f[I]message_size\fP
The size in bytes of the location in which to store the returned message.
.TP 8n
\f[I]errnum\fP
The error value to be decoded, usually obtained from the \f[I]errno\fP
global variable just before this function is called. This is necessary if
you need to call \f[B]any\fP code between the system call to be explained
and this function, because many libc functions will alter the value of
\f[I]errno\fP.
.TP 8n
\f[I]which\fP
The original which, exactly as passed to the \f[I]setpriority\fP(2) system
call.
.TP 8n
\f[I]who\fP
The original who, exactly as passed to the \f[I]setpriority\fP(2) system
call.
.TP 8n
\f[I]prio\fP
The original prio, exactly as passed to the \f[I]setpriority\fP(2) system
call.
.PP
\f[B]Example:\fP This function is intended to be used in a fashion similar
to the following example:
.RS
.ft CW
.fi
.ad l
if (setpriority(which, who, prio) < 0)
.ad b
.nf
{
    int err = errno;
    char message[3000];
.in +4n
.fi
.ad l
explain_message_errno_setpriority(message, sizeof(message), err, which,
who, prio);
.nf
.in -4n
    fprintf(stderr, "%s\en", message);
    exit(EXIT_FAILURE);
}
.fi
.ft R
.ad b
.RE
.PP
The above code example is available pre\-packaged as the
\f[I]explain_setpriority_or_die\fP(3) function.
.\" ----------------------------------------------------
.SH SEE ALSO
.TP 8n
\f[I]setpriority\fP(2)
set program scheduling priority
.TP 8n
\f[I]explain_setpriority_or_die\fP(3)
set program scheduling priority and report errors
.\" ----------------------------------------------------
.SH COPYRIGHT
.so etc/version.so
.if n .ds C) (C)
.if t .ds C) \(co
libexplain version \*(v)
.br
Copyright \*(C) 2013 Peter Miller
.\" vim: set ts=8 sw=4 et :