explain_openat(3)

💖 explain_openat(3) — Library Functions Manual 💖

okay bestie, welcome to explain_openat(3), straight out of the Library Functions Manual. this is the page that teaches you how to get actual explanations for your openat(2) errors instead of just squinting at a number and crying. 🫶

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✨ NAME ✨

explain_openat — explain openat(2) errors

like. it explains them. that's the whole job. 💅

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🌸 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);

four functions, one header, zero drama. 🌈

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🦋 DESCRIPTION 🦋

so these functions are your little translators 🧚 — you use them to obtain explanations for errors returned by the openat(2) system call. that's it, that's the vibe.

💜 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. like, it ate and left no crumbs. 👑

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. exactly. don't get creative with it. 🙈
• 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. 😭 it's giving communal. it's giving "who touched my message buffer".

Note: this function is not thread safe, because it shares a return buffer across all threads, and many other functions in this library. no cap. be careful out there bestie.

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. convenient queen. 💅

🎀 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. same energy, but you hand it the error number yourself. ✨

• 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. yes, errno is that friend that changes the second you look away. 💀
• 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. oh she's responsible. she brought her own buffer. 🫶
• 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.

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🌈 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

iykyk. go read those next, bestie. 📚

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👑 COPYRIGHT 👑

libexplain version 1.4 Copyright (C) 2013 Peter Miller

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okay that's the whole page!! 🎀 this was explain_openat(3) from the Library Functions Manual, brought to you by libexplain version 1.4, Copyright (C) 2013 Peter Miller — and there's no date stamped on this one, so that's literally all the sign-off info we got, bestie. go forth, explain your errors, and slay. 💖✨🦋