explain_openat man page

explain_openat — explain openat(2) errors

Synopsis

#include <libexplain/openat.h>

const char *explain_openat(int fildes, const char *pathname, int flags, mode_t mode);
const char *explain_errno_openat(int errnum, int fildes, const char *pathname, int flags, mode_t mode);
void explain_message_openat(char *message, int message_size, int fildes, const char *pathname, int flags, mode_t mode);
void explain_message_errno_openat(char *message, int message_size, int errnum, int fildes, const char *pathname, int flags, mode_t mode);

Description

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

explain_openat

const char *explain_openat(int fildes, const char *pathname, int flags, mode_t mode);

The explain_openat function is used to obtain an explanation of an error returned by the openat(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.

fildes
The original fildes, exactly as passed to the openat(2) system call.
pathname
The original pathname, exactly as passed to the openat(2) system call.
flags
The original flags, exactly as passed to the openat(2) system call.
mode
The original mode, exactly as passed to the openat(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:

int result = openat(fildes, pathname, flags, mode);
if (result < 0)

{

fprintf(stderr, "%s\n", explain_openat(fildes, pathname, flags, mode));

    exit(EXIT_FAILURE);
}

The above code example is available pre-packaged as the explain_openat_or_die(3) function.

explain_errno_openat

const char *explain_errno_openat(int errnum, int fildes, const char *pathname, int flags, mode_t mode);

The explain_errno_openat function is used to obtain an explanation of an error returned by the openat(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.

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 openat(2) system call.
pathname
The original pathname, exactly as passed to the openat(2) system call.
flags
The original flags, exactly as passed to the openat(2) system call.
mode
The original mode, exactly as passed to the openat(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:

int result = openat(fildes, pathname, flags, mode);
if (result < 0)

{
    int err = errno;

fprintf(stderr, "%s\n", explain_errno_openat(err, fildes, pathname, flags, mode));

    exit(EXIT_FAILURE);
}

The above code example is available pre-packaged as the explain_openat_or_die(3) function.

explain_message_openat

void explain_message_openat(char *message, int message_size, int fildes, const char *pathname, int flags, mode_t mode);

The explain_message_openat function is used to obtain an explanation of an error returned by the openat(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.

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 openat(2) system call.
pathname
The original pathname, exactly as passed to the openat(2) system call.
flags
The original flags, exactly as passed to the openat(2) system call.
mode
The original mode, exactly as passed to the openat(2) system call.

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

int result = openat(fildes, pathname, flags, mode);
if (result < 0)

{
    char message[3000];

explain_message_openat(message, sizeof(message), fildes, pathname, flags, mode);

    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

The above code example is available pre-packaged as the explain_openat_or_die(3) function.

explain_message_errno_openat

void explain_message_errno_openat(char *message, int message_size, int errnum, int fildes, const char *pathname, int flags, mode_t mode);

The explain_message_errno_openat function is used to obtain an explanation of an error returned by the openat(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.

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 openat(2) system call.
pathname
The original pathname, exactly as passed to the openat(2) system call.
flags
The original flags, exactly as passed to the openat(2) system call.
mode
The original mode, exactly as passed to the openat(2) system call.

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

int result = openat(fildes, pathname, flags, mode);
if (result < 0)

{
    int err = errno;
    char message[3000];

explain_message_errno_openat(message, sizeof(message), err, fildes, pathname, flags, mode);

    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

The above code example is available pre-packaged as the explain_openat_or_die(3) function.

See Also

openat(2)
open a file relative to a directory file descriptor
explain_openat_or_die(3)
open a file relative to a directory file descriptor and report errors

Referenced By

explain(3), explain_openat_or_die(3).