libexplain/pread.h File Reference

explain pread(2) errors More...

#include <libexplain/gcc_attributes.h>
#include <libexplain/large_file_support.h>
#include <unistd.h>

Go to the source code of this file.

Functions
ssize_t	explain_pread_or_die (int fildes, void *data, size_t data_size, off_t offset) LIBEXPLAIN_WARN_UNUSED_RESULT
ssize_t	explain_pread_on_error (int fildes, void *data, size_t data_size, off_t offset) LIBEXPLAIN_WARN_UNUSED_RESULT
const char *	explain_pread (int fildes, void *data, size_t data_size, off_t offset) LIBEXPLAIN_WARN_UNUSED_RESULT
const char *	explain_errno_pread (int errnum, int fildes, void *data, size_t data_size, off_t offset) LIBEXPLAIN_WARN_UNUSED_RESULT
void	explain_message_pread (char *message, int message_size, int fildes, void *data, size_t data_size, off_t offset)
void	explain_message_errno_pread (char *message, int message_size, int errnum, int fildes, void *data, size_t data_size, off_t offset)

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Detailed Description

explain pread(2) errors

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

Definition in file pread.h.

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Function Documentation

const char* explain_errno_pread	(	int	errnum,
		int	fildes,
		void *	data,
		size_t	data_size,
		off_t	offset
	)

The explain_errno_pread function is used to obtain an explanation of an error returned by the pread(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.
fildes	The original fildes, exactly as passed to the pread(2) system call.
data	The original data, exactly as passed to the pread(2) system call.
data_size	The original data_size, exactly as passed to the pread(2) system call.
offset	The original offset, exactly as passed to the pread(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:

 ssize_t result = pread(fildes, data, data_size, offset);
 if (result < 0)
 {
     int err = errno;
     fprintf(stderr, "%s\n", explain_errno_pread(err, fildes, data,
         data_size, offset));
     exit(EXIT_FAILURE);
 }

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

void explain_message_errno_pread	(	char *	message,
		int	message_size,
		int	errnum,
		int	fildes,
		void *	data,
		size_t	data_size,
		off_t	offset
	)

The explain_message_errno_pread function is used to obtain an explanation of an error returned by the pread(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.
fildes	The original fildes, exactly as passed to the pread(2) system call.
data	The original data, exactly as passed to the pread(2) system call.
data_size	The original data_size, exactly as passed to the pread(2) system call.
offset	The original offset, exactly as passed to the pread(2) system call.

Example:

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

 ssize_t result = pread(fildes, data, data_size, offset);
 if (result < 0)
 {
     int err = errno;
     char message[3000];
     explain_message_errno_pread(message, sizeof(message), err, fildes, data,
         data_size, offset);
     fprintf(stderr, "%s\n", message);
     exit(EXIT_FAILURE);
 }

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

void explain_message_pread	(	char *	message,
		int	message_size,
		int	fildes,
		void *	data,
		size_t	data_size,
		off_t	offset
	)

The explain_message_pread function is used to obtain an explanation of an error returned by the pread(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.
fildes	The original fildes, exactly as passed to the pread(2) system call.
data	The original data, exactly as passed to the pread(2) system call.
data_size	The original data_size, exactly as passed to the pread(2) system call.
offset	The original offset, exactly as passed to the pread(2) system call.

Example:

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

 ssize_t result = pread(fildes, data, data_size, offset);
 if (result < 0)
 {
     char message[3000];
     explain_message_pread(message, sizeof(message), fildes, data, data_size,
         offset);
     fprintf(stderr, "%s\n", message);
     exit(EXIT_FAILURE);
 }

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

const char* explain_pread	(	int	fildes,
		void *	data,
		size_t	data_size,
		off_t	offset
	)

The explain_pread function is used to obtain an explanation of an error returned by the pread(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.

Parameters:

fildes	The original fildes, exactly as passed to the pread(2) system call.
data	The original data, exactly as passed to the pread(2) system call.
data_size	The original data_size, exactly as passed to the pread(2) system call.
offset	The original offset, exactly as passed to the pread(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:

 ssize_t result = pread(fildes, data, data_size, offset);
 if (result < 0)
 {
     fprintf(stderr, "%s\n", explain_pread(fildes, data, data_size, offset));
     exit(EXIT_FAILURE);
 }

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

ssize_t explain_pread_on_error	(	int	fildes,
		void *	data,
		size_t	data_size,
		off_t	offset
	)

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

Parameters:

fildes	The fildes, exactly as to be passed to the pread(2) system call.
data	The data, exactly as to be passed to the pread(2) system call.
data_size	The data_size, exactly as to be passed to the pread(2) system call.
offset	The offset, exactly as to be passed to the pread(2) system call.

Returns:

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

Example:

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

 ssize_t result = explain_pread_on_error(fildes, data, data_size, offset);
 if (result < 0)
 {
     ...cope with error
     ...no need to print error message
 }

ssize_t explain_pread_or_die	(	int	fildes,
		void *	data,
		size_t	data_size,
		off_t	offset
	)

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

Parameters:

fildes	The fildes, exactly as to be passed to the pread(2) system call.
data	The data, exactly as to be passed to the pread(2) system call.
data_size	The data_size, exactly as to be passed to the pread(2) system call.
offset	The offset, exactly as to be passed to the pread(2) system call.

Returns:

This function only returns on success, see pread(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:

 ssize_t result = explain_pread_or_die(fildes, data, data_size, offset);