SYNOPSIS

#include <libexplain/setpgrp.h>

const char *explain_setpgrp(pid_t pid, pid_t pgid);
const char *explain_errno_setpgrp(int errnum, pid_t pid, pid_t pgid);
void explain_message_setpgrp(char *message, int message_size, pid_t pid, pid_t pgid);
void explain_message_errno_setpgrp(char *message, int message_size, int errnum, pid_t pid, pid_t pgid);

DESCRIPTION

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

Note: the setpgrp(2) function has two implementations. The System V version has no arguments, while the BSD version has two arguments. For simplicity of implementation, the argument list seen here includes the pid and pgid arguments.

The System V getpgid() semantics can be obtained by calling setpgrp(0, 0) on systems with the BSD version, and this is the API for libexplain, even on systems that do not use the BSD API.

explain_setpgrp

const char *explain_setpgrp(pid_t pid, pid_t pgid);

The explain_setpgrp function is used to obtain an explanation of an error returned by the setpgrp(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.

pid

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

pgid

The original pgid, exactly as passed to the setpgrp(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:

if (setpgrp(pid, pgid) < 0)

{

fprintf(stderr, "%s\n", explain_setpgrp(pid, pgid));

    exit(EXIT_FAILURE);
}

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

explain_errno_setpgrp

const char *explain_errno_setpgrp(int errnum, pid_t pid, pid_t pgid);

The explain_errno_setpgrp function is used to obtain an explanation of an error returned by the setpgrp(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.

pid

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

pgid

The original pgid, exactly as passed to the setpgrp(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:

if (setpgrp(pid, pgid) < 0)

{
    int err = errno;

fprintf(stderr, "%s\n", explain_errno_setpgrp(err, pid, pgid));

    exit(EXIT_FAILURE);
}

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

explain_message_setpgrp

void explain_message_setpgrp(char *message, int message_size, pid_t pid, pid_t pgid);

The explain_message_setpgrp function is used to obtain an explanation of an error returned by the setpgrp(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.

pid

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

pgid

The original pgid, exactly as passed to the setpgrp(2) system call.

Example: This function is intended to be used in a fashion similar to the following example:

if (setpgrp(pid, pgid) < 0)

{
    char message[3000];

explain_message_setpgrp(message, sizeof(message), pid, pgid);

    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

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

explain_message_errno_setpgrp

void explain_message_errno_setpgrp(char *message, int message_size, int errnum, pid_t pid, pid_t pgid);

The explain_message_errno_setpgrp function is used to obtain an explanation of an error returned by the setpgrp(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.

pid

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

pgid

The original pgid, exactly as passed to the setpgrp(2) system call.

Example: This function is intended to be used in a fashion similar to the following example:

if (setpgrp(pid, pgid) < 0)

{
    int err = errno;
    char message[3000];

explain_message_errno_setpgrp(message, sizeof(message), err, pid, pgid);

    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

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

COPYRIGHT

libexplain version 1.4
Copyright (C) 2011 Peter Miller