explain_eventfd(3)

NAME
explain_eventfd - explain eventfd(2) errors

SYNOPSIS
#include <libexplain/eventfd.h>

const char *explain_eventfd(unsigned int initval, int flags);
const char *explain_errno_eventfd(int errnum, unsigned int initval, int flags);
void explain_message_eventfd(char *message, int message_size, unsigned int initval, int flags);
void explain_message_errno_eventfd(char *message, int message_size, int errnum, unsigned int initval, int flags);

DESCRIPTION
These functions may be used to obtain explanations for errors returned by the eventfd(2) system call.

  explain_eventfd
const char *explain_eventfd(unsigned int initval, int flags);

The explain_eventfd function is used to obtain an explanation of an error returned by the eventfd(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 errno global variable will be used to obtain the error value to be decoded.

initval
    The original initval, exactly as passed to the eventfd(2) system call.

flags
    The original flags, exactly as passed to the eventfd(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.

Example: This function is intended to be used in a fashion similar to the following example:
    int result = eventfd(initval, flags);
    if (result < 0)
    {
    fprintf(stderr, "%s\n", explain_eventfd(initval, flags));
        exit(EXIT_FAILURE);
    }

The above code example is available pre-packaged as the explain_eventfd_or_die(3) function.

  explain_errno_eventfd
const char *explain_errno_eventfd(int errnum, unsigned int initval, int flags);

The explain_errno_eventfd function is used to obtain an explanation of an error returned by the eventfd(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.

errnum
    The error value to be decoded, usually obtained 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.

initval
    The original initval, exactly as passed to the eventfd(2) system call.

flags
    The original flags, exactly as passed to the eventfd(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.

Example: This function is intended to be used in a fashion similar to the following example:
    int result = eventfd(initval, flags);
    if (result < 0)
    {
        int err = errno;
    fprintf(stderr, "%s\n", explain_errno_eventfd(err, initval, flags));
        exit(EXIT_FAILURE);
    }

The above code example is available pre-packaged as the explain_eventfd_or_die(3) function.

  explain_message_eventfd
void explain_message_eventfd(char *message, int message_size, unsigned int initval, int flags);

The explain_message_eventfd function is used to obtain an explanation of an error returned by the eventfd(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 errno global variable will be used to obtain the error value to be decoded.

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

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

initval
    The original initval, exactly as passed to the eventfd(2) system call.

flags
    The original flags, exactly as passed to the eventfd(2) system call.

Example: This function is intended to be used in a fashion similar to the following example:
    int result = eventfd(initval, flags);
    if (result < 0)
    {
        char message[3000];
    explain_message_eventfd(message, sizeof(message), initval, flags);
        fprintf(stderr, "%s\n", message);
        exit(EXIT_FAILURE);
    }

The above code example is available pre-packaged as the explain_eventfd_or_die(3) function.

  explain_message_errno_eventfd
void explain_message_errno_eventfd(char *message, int message_size, int errnum, unsigned int initval, int flags);

The explain_message_errno_eventfd function is used to obtain an explanation of an error returned by the eventfd(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.

message
    The location in which to store the returned message. If a suitable message return buffer is 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 obtained 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.

initval
    The original initval, exactly as passed to the eventfd(2) system call.

flags
    The original flags, exactly as passed to the eventfd(2) system call.

Example: This function is intended to be used in a fashion similar to the following example:
    int result = eventfd(initval, flags);
    if (result < 0)
    {
        int err = errno;
        char message[3000];
    explain_message_errno_eventfd(message, sizeof(message), err, initval, flags);
        fprintf(stderr, "%s\n", message);
        exit(EXIT_FAILURE);
    }

The above code example is available pre-packaged as the explain_eventfd_or_die(3) function.

SEE ALSO

eventfd(2)
    create a file descriptor for event notification

explain_eventfd_or_die(3)
    create a file descriptor for event notification and report errors

COPYRIGHT
libexplain version
Copyright (C) 2009 Peter Miller