.\"
.\" libexplain - Explain errno values returned by libc functions
.\" Copyright (C) 2008, 2009, 2011 Peter Miller
.\" Written by Peter Miller <pmiller@opensource.org.au>
.\"
.\" 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
.\" 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_read
.cp 0  \" Solaris defaults to ''.cp 1'', sheesh.
.TH explain_read 3
.SH NAME
explain_read \- explain read(2) errors
.if require_index \{
.XX "explain_read(3)" "explain read(2) errors"
.\}
.SH SYNOPSIS
#include <libexplain/read.h>
.br
const char *explain_read(int fildes, const void *data, long data_size);
.br
const char *explain_errno_read(int errnum, int fildes, const void *data,
long data_size);
.br
void explain_message_read(char *message, int message_size, int fildes,
const void *data, long data_size);
.br
void explain_message_errno_read(char *message, int message_size,
int errnum, int fildes, const void *data, long data_size);
.SH DESCRIPTION
These functions may be used to obtain an explanation for \f[I]read\fP(2)
errors.
.\" ------------------------------------------------------------------------
.SS explain_read
const char *explain_read(int fildes, const void *data, long data_size);
.PP
The explain_read function may be used to obtain a human readable
explanation of what went wrong in a \f[I]read\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 error number will be picked up from the \f[I]errno\fP global variable.
.PP
This function is intended to be used in a fashion similar to the
following example:
.RS
.ft CW
.nf
ssize_t n = read(fd, data, data_size);
if (n < 0)
{
    fprintf(stderr, "%s\en", explain_read(fd, data, data_size));
    exit(EXIT_FAILURE);
}
.fi
.ft R
.RE
.TP 8n
\f[I]fildes\fP
The original fildes,
exactly as passed to the \f[I]read\fP(2) system call.
.TP 8n
\f[I]data\fP
The original data,
exactly as passed to the \f[I]read\fP(2) system call.
.TP 8n
\f[I]data_size\fP
The original data_size,
exactly as passed to the \f[I]read\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.
.\" ------------------------------------------------------------------------
.SS explain_errno_read
const char *explain_errno_read(int errnum, int fildes, const void *data,
long data_size);
.PP
The explain_errno_read function may be used to obtain a human
readable explanation of what went wrong in a \f[I]read\fP(2)
system call.  The least the message will contain is the value of
\f[CW]strerror(errnum)\fP, but usually it will do much better, and
indicate the underlying cause in more detail.
.PP
This function is intended to be used in a fashion similar to the
following example:
.RS
.ft CW
.nf
ssize_t n = read(fd, data, data_size);
if (n < 0)
{
    int err = errno;
    fprintf(stderr, "%s\en", explain_errno_read(err, fd, data, data_size));
    exit(EXIT_FAILURE);
}
.fi
.ft R
.RE
.TP 8n
\f[I]errnum\fP
The error value to be decoded, usually obtain 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]fildes\fP
The original fildes,
exactly as passed to the \f[I]read\fP(2) system call.
.TP 8n
\f[I]data\fP
The original data,
exactly as passed to the \f[I]read\fP(2) system call.
.TP 8n
\f[I]data_size\fP
The original data_size,
exactly as passed to the \f[I]read\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.
.\" ------------------------------------------------------------------------
.SS explain_message_read
void explain_message_read(char *message, int message_size,
int fildes, const void *data, long data_size);
.PP
The explain_message_read function may be used to obtain a human
readable explanation of what went wrong in a \f[I]read\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 error number will be picked up from the \f[I]errno\fP global variable.
.PP
This function is intended to be used in a fashion similar to the
following example:
.RS
.ft CW
.nf
ssize_t n = read(fd, data, data_size);
if (n < 0)
{
    char message[3000];
    explain_message_read(message, sizeof(message), fd, data, data_size));
    fprintf(stderr, "%s\en", message);
    exit(EXIT_FAILURE);
}
.fi
.ft R
.RE
.TP 8n
\f[I]message\fP
The location in which to store the returned message.  Because a message
return buffer has been 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]fildes\fP
The original fildes,
exactly as passed to the \f[I]read\fP(2) system call.
.TP 8n
\f[I]data\fP
The original data,
exactly as passed to the \f[I]read\fP(2) system call.
.TP 8n
\f[I]data_size\fP
The original data_size,
exactly as passed to the \f[I]read\fP(2) system call.
.PP
\f[B]Note:\fP
Given a suitably thread safe buffer, this function is thread safe.
.\" ------------------------------------------------------------------------
.SS explain_message_errno_read
void explain_message_errno_read(char *message, int message_size, int errnum,
int fildes, const void *data, long data_size);
.PP
The explain_message_errno_read function may be used to obtain a
human readable explanation of what went wrong in a \f[I]read\fP(2)
system call.  The least the message will contain is the value of
\f[CW]strerror(errnum)\fP, but usually it will do much better, and
indicate the underlying cause in more detail.
.PP
This function is intended to be used in a fashion similar to the
following example:
.RS
.ft CW
.nf
ssize_t n = read(fd, data, data_size);
if (n < 0)
{
    int err = errno;
    char message[3000];
    explain_message_errno_read(message, sizeof(message), err,
        fd, data, data_size);
    fprintf(stderr, "%s\en", message);
    exit(EXIT_FAILURE);
}
.fi
.ft R
.RE
.TP 8n
\f[I]message\fP
The location in which to store the returned message.  Because a message
return buffer has been 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 obtain 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]fildes\fP
The original fildes,
exactly as passed to the \f[I]read\fP(2) system call.
.TP 8n
\f[I]data\fP
The original data,
exactly as passed to the \f[I]read\fP(2) system call.
.TP 8n
\f[I]data_size\fP
The original data_size,
exactly as passed to the \f[I]read\fP(2) system call.
.PP
\f[B]Note:\fP
Given a suitably thread safe buffer, this function is thread safe.
.\" ------------------------------------------------------------------------
.SH COPYRIGHT
.so etc/version.so
.if n .ds C) (C)
.if t .ds C) \(co
libexplain version \*(v)
.br
Copyright \*(C) 2008 Peter Miller
.SH AUTHOR
Written by Peter Miller <pmiller@opensource.org.au>