explain_getpgrp man page

explain_getpgrp — explain getpgrp(2) errors

Synopsis

#include <libexplain/getpgrp.h>

const char *explain_getpgrp(pid_t pid);
const char *explain_errno_getpgrp(int errnum, pid_t pid);
void explain_message_getpgrp(char *message, int message_size, pid_t pid);
void explain_message_errno_getpgrp(char *message, int message_size, int errnum, pid_t pid);

Description

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

Note: the getpgrp(2) function has two implementations. The POSIX.1 version has no arguments, while the BSD version has one argument. For simplicity of implementation, the argument list seen here includes the pid argument.

The POSIX.1 getpgid() semantics can be obtained by calling getpgrp(0) on BSD systems, and this is the API for libexplain, even on systems that do not use the BSD API.

explain_getpgrp

const char *explain_getpgrp(pid_t pid);

The explain_getpgrp function is used to obtain an explanation of an error returned by the getpgrp(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 getpgrp(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:

pid_t result = getpgrp(pid);
if (result < 0)

{

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

    exit(EXIT_FAILURE);
}

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

explain_errno_getpgrp

const char *explain_errno_getpgrp(int errnum, pid_t pid);

The explain_errno_getpgrp function is used to obtain an explanation of an error returned by the getpgrp(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 getpgrp(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:

pid_t result = getpgrp(pid);
if (result < 0)

{
    int err = errno;

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

    exit(EXIT_FAILURE);
}

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

explain_message_getpgrp

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

The explain_message_getpgrp function is used to obtain an explanation of an error returned by the getpgrp(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 getpgrp(2) system call.

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

pid_t result = getpgrp(pid);
if (result < 0)

{
    char message[3000];

explain_message_getpgrp(message, sizeof(message), pid);

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

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

explain_message_errno_getpgrp

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

The explain_message_errno_getpgrp function is used to obtain an explanation of an error returned by the getpgrp(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 getpgrp(2) system call.

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

pid_t result = getpgrp(pid);
if (result < 0)

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

explain_message_errno_getpgrp(message, sizeof(message), err, pid);

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

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

See Also

getpgrp(2)
get process group
explain_getpgrp_or_die(3)
get process group and report errors

Referenced By

explain(3), explain_getpgrp_or_die(3).