explain_select man page

explain_select — explain select(2) errors

Synopsis

#include <sys/select.h> #include <libexplain/select.h>

const char *explain_select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);
const char *explain_errno_select(int errnum, int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);
void explain_message_select(char *message, int message_size, int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);
void explain_message_errno_select(char *message, int message_size, int errnum, int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);

Description

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

explain_select

const char *explain_select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);

The explain_select function is used to obtain an explanation of an error returned by the select(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 (select(nfds, readfds, writefds, exceptfds, timeout) < 0)
{
    fprintf(stderr, "%s\n", explain_select(nfds,
        readfds, writefds, exceptfds, timeout));
    exit(EXIT_FAILURE);
}
nfds

The original nfds, exactly as passed to the select(2) system call.

readfds

The original readfds, exactly as passed to the select(2) system call.

writefds

The original writefds, exactly as passed to the select(2) system call.

exceptfds

The original exceptfds, exactly as passed to the select(2) system call.

timeout

The original timeout, exactly as passed to the select(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_select

const char *explain_errno_select(int errnum, int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);

The explain_errno_select function is used to obtain an explanation of an error returned by the select(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 (select(nfds, readfds, writefds, exceptfds, timeout) < 0)
{
    int err = errno;
    fprintf(stderr, "%s\n", explain_errno_select(err,
        nfds, readfds, writefds, exceptfds, timeout));
    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.

nfds

The original nfds, exactly as passed to the select(2) system call.

readfds

The original readfds, exactly as passed to the select(2) system call.

writefds

The original writefds, exactly as passed to the select(2) system call.

exceptfds

The original exceptfds, exactly as passed to the select(2) system call.

timeout

The original timeout, exactly as passed to the select(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_select

void explain_message_select(char *message, int message_size, int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);

The explain_message_select function may be used to  obtain an explanation of an error returned by the select(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 (select(nfds, readfds, writefds, exceptfds, timeout) < 0)
{
    char message[3000];
    explain_message_select(message, sizeof(message),
        nfds, readfds, writefds, exceptfds, timeout);
    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.

nfds

The original nfds, exactly as passed to the select(2) system call.

readfds

The original readfds, exactly as passed to the select(2) system call.

writefds

The original writefds, exactly as passed to the select(2) system call.

exceptfds

The original exceptfds, exactly as passed to the select(2) system call.

timeout

The original timeout, exactly as passed to the select(2) system call.

explain_message_errno_select

void explain_message_errno_select(char *message, int message_size, int errnum, int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);

The explain_message_errno_select function may be used to obtain an explanation of an error returned by the select(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 (select(nfds, readfds, writefds, exceptfds, timeout) < 0)
{
    int err = errno;
    char message[3000];
    explain_message_errno_select(message, sizeof(message), err,
        nfds, readfds, writefds, exceptfds, timeout);
    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.

nfds

The original nfds, exactly as passed to the select(2) system call.

readfds

The original readfds, exactly as passed to the select(2) system call.

writefds

The original writefds, exactly as passed to the select(2) system call.

exceptfds

The original exceptfds, exactly as passed to the select(2) system call.

timeout

The original timeout, exactly as passed to the select(2) system call.

See Also

select(2)

blah blah

explain_select_or_die(3)

blah blah and report errors

Referenced By

explain(3), explain_select_or_die(3).