libexplain/readlink.h File Reference

explain readlink(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_readlink_or_die (const char *pathname, char *data, size_t data_size)
ssize_t	explain_readlink_on_error (const char *pathname, char *data, size_t data_size) LIBEXPLAIN_WARN_UNUSED_RESULT
const char *	explain_readlink (const char *pathname, char *data, size_t data_size) LIBEXPLAIN_WARN_UNUSED_RESULT
const char *	explain_errno_readlink (int errnum, const char *pathname, char *data, size_t data_size) LIBEXPLAIN_WARN_UNUSED_RESULT
void	explain_message_readlink (char *message, int message_size, const char *pathname, char *data, size_t data_size)
void	explain_message_errno_readlink (char *message, int message_size, int errnum, const char *pathname, char *data, size_t data_size)

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Detailed Description

explain readlink(2) errors

Definition in file readlink.h.

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Function Documentation

const char* explain_errno_readlink	(	int	errnum,
		const char *	pathname,
		char *	data,
		size_t	data_size
	)

The explain_errno_readlink function is used to obtain an explanation of an error returned by the readlink(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:

 ssize_t result = readlink(pathname, data, data_size);
 if (result < 0)
 {
     int err = errno;
     fprintf(stderr, "%s\n", explain_errno_readlink(err, pathname, data,
         data_size));
     exit(EXIT_FAILURE);
 }

The above code example is available pre-packaged as the explain_readlink_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.
pathname	The original pathname, exactly as passed to the readlink(2) system call.
data	The original data, exactly as passed to the readlink(2) system call.
data_size	The original data_size, exactly as passed to the readlink(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_readlink	(	char *	message,
		int	message_size,
		int	errnum,
		const char *	pathname,
		char *	data,
		size_t	data_size
	)

The explain_message_errno_readlink function is used to obtain an explanation of an error returned by the readlink(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:

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

The above code example is available pre-packaged as the explain_readlink_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.
pathname	The original pathname, exactly as passed to the readlink(2) system call.
data	The original data, exactly as passed to the readlink(2) system call.
data_size	The original data_size, exactly as passed to the readlink(2) system call.

void explain_message_readlink	(	char *	message,
		int	message_size,
		const char *	pathname,
		char *	data,
		size_t	data_size
	)

The explain_message_readlink function is used to obtain an explanation of an error returned by the readlink(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:

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

The above code example is available pre-packaged as the explain_readlink_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.
pathname	The original pathname, exactly as passed to the readlink(2) system call.
data	The original data, exactly as passed to the readlink(2) system call.
data_size	The original data_size, exactly as passed to the readlink(2) system call.

const char* explain_readlink	(	const char *	pathname,
		char *	data,
		size_t	data_size
	)

The explain_readlink function is used to obtain an explanation of an error returned by the readlink(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:

 ssize_t result = readlink(pathname, data, data_size);
 if (result < 0)
 {
     fprintf(stderr, "%s\n", explain_readlink(pathname, data, data_size));
     exit(EXIT_FAILURE);
 }

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

Parameters:

pathname	The original pathname, exactly as passed to the readlink(2) system call.
data	The original data, exactly as passed to the readlink(2) system call.
data_size	The original data_size, exactly as passed to the readlink(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.

ssize_t explain_readlink_on_error	(	const char *	pathname,
		char *	data,
		size_t	data_size
	)

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

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

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

Parameters:

pathname	The pathname, exactly as to be passed to the readlink(2) system call.
data	The data, exactly as to be passed to the readlink(2) system call.
data_size	The data_size, exactly as to be passed to the readlink(2) system call.

Returns:

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

ssize_t explain_readlink_or_die	(	const char *	pathname,
		char *	data,
		size_t	data_size
	)

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

 ssize_t result = explain_readlink_or_die(pathname, data, data_size);

Parameters:

pathname	The pathname, exactly as to be passed to the readlink(2) system call.
data	The data, exactly as to be passed to the readlink(2) system call.
data_size	The data_size, exactly as to be passed to the readlink(2) system call.

Returns:

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