libexplain/wait4.h File Reference

explain wait4(2) errors More...

#include <libexplain/gcc_attributes.h>

Go to the source code of this file.

Functions
int	explain_wait4_or_die (int pid, int *status, int options, struct rusage *rusage)
int	explain_wait4_on_error (int pid, int *status, int options, struct rusage *rusage) LIBEXPLAIN_WARN_UNUSED_RESULT
const char *	explain_wait4 (int pid, int *status, int options, struct rusage *rusage) LIBEXPLAIN_WARN_UNUSED_RESULT
const char *	explain_errno_wait4 (int errnum, int pid, int *status, int options, struct rusage *rusage) LIBEXPLAIN_WARN_UNUSED_RESULT
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)

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Detailed Description

explain wait4(2) errors

Definition in file wait4.h.

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Function Documentation

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:

 pid_t pid = wait4(pid, status, options, rusage);
 if (pid < 0)
 {
     int err = errno;
     fprintf(stderr, "%s\n", explain_errno_wait4(err, pid, status, options,
         rusage));
     exit(EXIT_FAILURE);
 }

The above code example is available pre-packaged as the explain_wait4_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.
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.

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 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:

 pid_t pid = wait4(pid, status, options, rusage);
 if (pid < 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);
 }

The above code example is available pre-packaged as the explain_wait4_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.
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.

void explain_message_wait4	(	char *	message,
		int	message_size,
		int	pid,
		int *	status,
		int	options,
		struct rusage *	rusage
	)

The explain_message_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.

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:

 pid_t pid = wait4(pid, status, options, rusage);
 if (pid < 0)
 {
     char message[3000];
     explain_message_wait4(message, sizeof(message), pid, status, options,
         rusage);
     fprintf(stderr, "%s\n", message);
     exit(EXIT_FAILURE);
 }

The above code example is available pre-packaged as the explain_wait4_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.
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.

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:

 pid_t pid = wait4(pid, status, options, rusage);
 if (pid < 0)
 {
     fprintf(stderr, "%s\n", explain_wait4(pid, status, options, rusage));
     exit(EXIT_FAILURE);
 }

The above code example is available pre-packaged as the explain_wait4_or_die function.

Parameters:

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.

int explain_wait4_on_error	(	int	pid,
		int *	status,
		int	options,
		struct rusage *	rusage
	)

The explain_wait4_on_error function is used to call the wait4(2) system call. On failure an explanation will be printed to stderr, obtained from the explain_wait4(3) function.

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

 pid_t pid = explain_wait4_on_error(pid, status, options, rusage);
 if (pid < 0)
 {
     ...cope with error
     ...no need to print error message
 }

Parameters:

pid	The pid, exactly as to be passed to the wait4(2) system call.
status	The status, exactly as to be passed to the wait4(2) system call.
options	The options, exactly as to be passed to the wait4(2) system call.
rusage	The rusage, exactly as to be passed to the wait4(2) system call.

Returns:

The value returned by the wrapped wait4(2) system call.

int explain_wait4_or_die	(	int	pid,
		int *	status,
		int	options,
		struct rusage *	rusage
	)

The explain_wait4_or_die function is used to call the wait4(2) system call. On failure an explanation will be printed to stderr, obtained from the explain_wait4(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:

 pid_t pid = explain_wait4_or_die(pid, status, options, rusage);

Parameters:

pid	The pid, exactly as to be passed to the wait4(2) system call.
status	The status, exactly as to be passed to the wait4(2) system call.
options	The options, exactly as to be passed to the wait4(2) system call.
rusage	The rusage, exactly as to be passed to the wait4(2) system call.

Returns:

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