explain_wait4(3)

NAME
explain_wait4 - explain wait4(2) errors

SYNOPSIS
#include <libexplain/wait4.h>

const char *explain_wait4(int pid, int *status, int options, struct rusage *rusage);
const char *explain_errno_wait4(int errnum, int pid, int *status, int options, struct rusage *rusage);
void explain_message_wait4(char *message, int message_size, int pid, int *status, int options, struct rusage *rusage);
void explain_message_errno_wait4(char *message, int message_size, int errnum, int pid, int *status, int options, struct rusage *rusage);

DESCRIPTION
These functions may be used to obtain explanations for errors returned by the wait4(2) system call.

  explain_wait4
const char *explain_wait4(int pid, int *status, int options, struct rusage *rusage);

The explain_wait4 function is used to obtain an explanation of an error returned by the wait4(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.

This function is intended to be used in a fashion similar to the following example:
    if (wait4(pid, status, options, rusage) < 0)
    {
        fprintf(stderr, "%s\n", explain_wait4(pid, status, options, rusage));
        exit(EXIT_FAILURE);
    }

pid The original pid, exactly as passed to the wait4(2) system call.

status
    The original status, exactly as passed to the wait4(2) system call.

options
    The original options, exactly as passed to the wait4(2) system call.

rusage
    The original rusage, exactly as passed to the wait4(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_wait4
const char *explain_errno_wait4(int errnum, int pid, int *status, int options, struct rusage *rusage);

The explain_errno_wait4 function is used to obtain an explanation of an error returned by the wait4(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:
    if (wait4(pid, status, options, rusage) < 0)
    {
        int err = errno;
        fprintf(stderr, "%s\n", explain_errno_wait4(err,
            pid, status, options, rusage));
        exit(EXIT_FAILURE);
    }

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.

pid The original pid, exactly as passed to the wait4(2) system call.

status
    The original status, exactly as passed to the wait4(2) system call.

options
    The original options, exactly as passed to the wait4(2) system call.

rusage
    The original rusage, exactly as passed to the wait4(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_wait4
void explain_message_wait4(char *message, int message_size, int pid, int *status, int options, struct rusage *rusage);

The explain_message_wait4 function may be used to obtain an explanation of an error returned by the wait4(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.

This function is intended to be used in a fashion similar to the following example:
    if (wait4(pid, status, options, rusage) < 0)
    {
        char message[3000];
        explain_message_wait4(message, sizeof(message),
            pid, status, options, rusage);
        fprintf(stderr, "%s\n", message);
        exit(EXIT_FAILURE);
    }

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.

pid The original pid, exactly as passed to the wait4(2) system call.

status
    The original status, exactly as passed to the wait4(2) system call.

options
    The original options, exactly as passed to the wait4(2) system call.

rusage
    The original rusage, exactly as passed to the wait4(2) system call.

  explain_message_errno_wait4
void explain_message_errno_wait4(char *message, int message_size, int errnum, int pid, int *status, int options, struct rusage *rusage);

The explain_message_errno_wait4 function may be used to obtain an explanation of an error returned by the wait4(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:
    if (wait4(pid, status, options, rusage) < 0)
    {
        int err = errno;
        char message[3000];
        explain_message_errno_wait4(message, sizeof(message), err,
            pid, status, options, rusage);
        fprintf(stderr, "%s\n", message);
        exit(EXIT_FAILURE);
    }

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.

pid The original pid, exactly as passed to the wait4(2) system call.

status
    The original status, exactly as passed to the wait4(2) system call.

options
    The original options, exactly as passed to the wait4(2) system call.

rusage
    The original rusage, exactly as passed to the wait4(2) system call.

SEE ALSO

wait4(2)
    wait for process to change state

explain_wait4_or_die(3)
    wait for process to change state and report errors

COPYRIGHT
libexplain version
Copyright (C) 2008 Peter Miller