explain_read(3)

NAME
explain_read - explain read(2) errors

SYNOPSIS
#include <libexplain/read.h>
const char *explain_read(int fildes, const void *data, long data_size);
const char *explain_errno_read(int errnum, int fildes, const void *data, long data_size);
void explain_message_read(char *message, int message_size, int fildes, const void *data, long data_size);
void explain_message_errno_read(char *message, int message_size, int errnum, int fildes, const void *data, long data_size);

DESCRIPTION
These functions may be used to obtain an explanation for read(2) errors.

  explain_read
const char *explain_read(int fildes, const void *data, long data_size);

The explain_read function may be used to obtain a human readable explanation of what went wrong in a read(2) system call. The least the message will contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail.

The error number will be picked up from the errno global variable.

This function is intended to be used in a fashion similar to the following example:
    ssize_t n = read(fd, data, data_size);
    if (n < 0)
    {
        fprintf(stderr, "%s\n", explain_read(fd, data, data_size));
        exit(EXIT_FAILURE);
    }

fildes
    The original fildes, exactly as passed to the read(2) system call.

data
    The original data, exactly as passed to the read(2) system call.

data_size
    The original data_size, exactly as passed to the read(2) system call.

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.

Note: This function is not thread safe, because it shares a return buffer across all threads, and many other functions in this library.

  explain_errno_read
const char *explain_errno_read(int errnum, int fildes, const void *data, long data_size);

The explain_errno_read function may be used to obtain a human readable explanation of what went wrong in a read(2) system call. The least the message will contain is the value of strerror(errnum), but usually it will do much better, and indicate the underlying cause in more detail.

This function is intended to be used in a fashion similar to the following example:
    ssize_t n = read(fd, data, data_size);
    if (n < 0)
    {
        int err = errno;
        fprintf(stderr, "%s\n", explain_errno_read(err, fd, data, data_size));
        exit(EXIT_FAILURE);
    }

errnum
    The error value to be decoded, usually obtain from the errno global variable just before this function is called. This is necessary if you need to call any code between the system call to be explained and this function, because many libc functions will alter the value of errno.

fildes
    The original fildes, exactly as passed to the read(2) system call.

data
    The original data, exactly as passed to the read(2) system call.

data_size
    The original data_size, exactly as passed to the read(2) system call.

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.

Note: This function is not thread safe, because it shares a return buffer across all threads, and many other functions in this library.

  explain_message_read
void explain_message_read(char *message, int message_size, int fildes, const void *data, long data_size);

The explain_message_read function may be used to obtain a human readable explanation of what went wrong in a read(2) system call. The least the message will contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail.

The error number will be picked up from the errno global variable.

This function is intended to be used in a fashion similar to the following example:
    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\n", message);
        exit(EXIT_FAILURE);
    }

message
    The location in which to store the returned message. Because a message return buffer has been supplied, this function is thread safe.

message_size
    The size in bytes of the location in which to store the returned message.

fildes
    The original fildes, exactly as passed to the read(2) system call.

data
    The original data, exactly as passed to the read(2) system call.

data_size
    The original data_size, exactly as passed to the read(2) system call.

Note: Given a suitably thread safe buffer, this function is thread safe.

  explain_message_errno_read
void explain_message_errno_read(char *message, int message_size, int errnum, int fildes, const void *data, long data_size);

The explain_message_errno_read function may be used to obtain a human readable explanation of what went wrong in a read(2) system call. The least the message will contain is the value of strerror(errnum), but usually it will do much better, and indicate the underlying cause in more detail.

This function is intended to be used in a fashion similar to the following example:
    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\n", message);
        exit(EXIT_FAILURE);
    }

message
    The location in which to store the returned message. Because a message return buffer has been supplied, this function is thread safe.

message_size
    The size in bytes of the location in which to store the returned message.

errnum
    The error value to be decoded, usually obtain from the errno global variable just before this function is called. This is necessary if you need to call any code between the system call to be explained and this function, because many libc functions will alter the value of errno.

fildes
    The original fildes, exactly as passed to the read(2) system call.

data
    The original data, exactly as passed to the read(2) system call.

data_size
    The original data_size, exactly as passed to the read(2) system call.

Note: Given a suitably thread safe buffer, this function is thread safe.

COPYRIGHT
libexplain version 1.1
Copyright (C) 2008 Peter Miller

AUTHOR
Written by Peter Miller <pmiller@opensource.org.au>