explain select(2) errors More...

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

Functions
int	explain_select_or_die (int nfds, fd_set readfds, fd_set writefds, fd_set exceptfds, struct timeval timeout)
int	explain_select_on_error (int nfds, fd_set readfds, fd_set writefds, fd_set exceptfds, struct timeval timeout) LIBEXPLAIN_WARN_UNUSED_RESULT
const char *	explain_select (int nfds, fd_set readfds, fd_set writefds, fd_set exceptfds, struct timeval timeout) LIBEXPLAIN_WARN_UNUSED_RESULT
const char *	explain_errno_select (int errnum, int nfds, fd_set readfds, fd_set writefds, fd_set exceptfds, struct timeval timeout) LIBEXPLAIN_WARN_UNUSED_RESULT
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)

Detailed Description

explain select(2) errors

Definition in file select.h.

Function Documentation

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);
 }

The above code example is available pre-packaged as the explain_select_or_die function.

Parameters:

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.

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 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;
     char message[3000];
     explain_message_errno_select(message, sizeof(message), err, nfds,
         readfds, writefds, exceptfds, timeout);
     fprintf(stderr, "%s\n", message);
     exit(EXIT_FAILURE);
 }

The above code example is available pre-packaged as the explain_select_or_die function.

Parameters:

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.

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 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.

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);
 }

The above code example is available pre-packaged as the explain_select_or_die function.

Parameters:

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.

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);
 }

The above code example is available pre-packaged as the explain_select_or_die function.

Parameters:

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.

int explain_select_on_error	(	int	nfds,
		fd_set *	readfds,
		fd_set *	writefds,
		fd_set *	exceptfds,
		struct timeval *	timeout
	)

The explain_select_on_error function is used to call the select(2) system call. On failure an explanation will be printed to stderr, obtained from the explain_select(3) function.

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

 if (explain_select_on_error(nfds, readfds, writefds, exceptfds, timeout)
     < 0)
 {
     ...cope with error
     ...no need to print error message
 }

Parameters:

nfds	The nfds, exactly as to be passed to the select(2) system call.
readfds	The readfds, exactly as to be passed to the select(2) system call.
writefds	The writefds, exactly as to be passed to the select(2) system call.
exceptfds	The exceptfds, exactly as to be passed to the select(2) system call.
timeout	The timeout, exactly as to be passed to the select(2) system call.

Returns:: The value returned by the wrapped select(2) system call.

int explain_select_or_die	(	int	nfds,
		fd_set *	readfds,
		fd_set *	writefds,
		fd_set *	exceptfds,
		struct timeval *	timeout
	)

The explain_select_or_die function is used to call the select(2) system call. On failure an explanation will be printed to stderr, obtained from the explain_select(3) function, and then the process terminates by calling exit(EXIT_FAILURE).

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

 explain_select_or_die(nfds, readfds, writefds, exceptfds, timeout);

Parameters:

nfds	The nfds, exactly as to be passed to the select(2) system call.
readfds	The readfds, exactly as to be passed to the select(2) system call.
writefds	The writefds, exactly as to be passed to the select(2) system call.
exceptfds	The exceptfds, exactly as to be passed to the select(2) system call.
timeout	The timeout, exactly as to be passed to the select(2) system call.

Returns:: This function only returns on success. On failure, prints an explanation and exits, it does not return.

Functions

Detailed Description

Function Documentation