libexplain/vfork.h File Reference

explain vfork(2) errors More...

#include <sys/types.h>
#include <unistd.h>
#include <libexplain/gcc_attributes.h>

Go to the source code of this file.

Functions
pid_t	explain_vfork_or_die (void) LIBEXPLAIN_WARN_UNUSED_RESULT
pid_t	explain_vfork_on_error (void) LIBEXPLAIN_WARN_UNUSED_RESULT
const char *	explain_vfork (void) LIBEXPLAIN_WARN_UNUSED_RESULT
const char *	explain_errno_vfork (int errnum) LIBEXPLAIN_WARN_UNUSED_RESULT
void	explain_message_vfork (char *message, int message_size)
void	explain_message_errno_vfork (char *message, int message_size, int errnum)

---

Detailed Description

explain vfork(2) errors

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

Definition in file vfork.h.

---

Function Documentation

const char* explain_errno_vfork

(

int

errnum

)

The explain_errno_vfork function is used to obtain an explanation of an error returned by the vfork(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.

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.

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 = vfork();
 if (result < 0)
 {
     int err = errno;
     fprintf(stderr, "%s\n", explain_errno_vfork(err, ));
     exit(EXIT_FAILURE);
 }

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

void explain_message_errno_vfork	(	char *	message,
		int	message_size,
		int	errnum
	)

The explain_message_errno_vfork function is used to obtain an explanation of an error returned by the vfork(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.

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.

Example:

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

 pid_t result = vfork();
 if (result < 0)
 {
     int err = errno;
     char message[3000];
     explain_message_errno_vfork(message, sizeof(message), err, );
     fprintf(stderr, "%s\n", message);
     exit(EXIT_FAILURE);
 }

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

void explain_message_vfork	(	char *	message,
		int	message_size
	)

The explain_message_vfork function is used to obtain an explanation of an error returned by the vfork(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.

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.

Example:

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

 pid_t result = vfork();
 if (result < 0)
 {
     char message[3000];
     explain_message_vfork(message, sizeof(message), );
     fprintf(stderr, "%s\n", message);
     exit(EXIT_FAILURE);
 }

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

const char* explain_vfork

(

void

)

The explain_vfork function is used to obtain an explanation of an error returned by the vfork(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.

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 = vfork();
 if (result < 0)
 {
     fprintf(stderr, "%s\n", explain_vfork());
     exit(EXIT_FAILURE);
 }

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

pid_t explain_vfork_on_error

(

void

)

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

Returns:

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

Example:

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

 pid_t result = explain_vfork_on_error();
 if (result < 0)
 {
     ...cope with error
     ...no need to print error message
 }

Note:

Because of vfork(2) usage limitations, and gcc barfs if you try to inline it, this actually calls fork(2).

“The vfork() function has the same effect as fork(2), except that the behavior is undefined if the process created by vfork() either modifies any data other than a variable of type pid_t used to store the return value from vfork(), or returns from the function in which vfork() was called, or calls any other function before successfully calling _exit(2) or one of the exec(3) family of functions.”

pid_t explain_vfork_or_die

(

void

)

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

Returns:

This function only returns on success, see vfork(2) for more information. On failure, prints an explanation and exits, it does not return.

Example:

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

 pid_t result = explain_vfork_or_die();

Note:

Because of vfork(2) usage limitations, and gcc barfs if you try to inline it, this actually calls fork(2).

“The vfork() function has the same effect as fork(2), except that the behavior is undefined if the process created by vfork() either modifies any data other than a variable of type pid_t used to store the return value from vfork(), or returns from the function in which vfork() was called, or calls any other function before successfully calling _exit(2) or one of the exec(3) family of functions.”