explain_open(3)

🎀 NAME 🎀

explain_open — she explains your open(2) errors, and she's so good at it 💅

This is the manual page for the explain_open(3) family of library functions, bestie. Settle in 🫶

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📖 SYNOPSIS 📖

#include <libexplain/open.h>
const char *explain_open(const char *pathname, int flags, int mode);
const char *explain_errno_open(int errnum, const char *pathname, int flags, int mode);
void explain_message_open(char *message, int message_size, const char *pathname, int flags, int mode);
void explain_message_errno_open(char *message, int message_size, int errnum, const char *pathname, int flags, int mode);

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🌈 DESCRIPTION 🌈

okay so the whole point of this little squad of functions: you can use them to obtain explanations for open(2) errors. That's the vibe. That's the assignment. And they ate. ✨

💖 explain_open(const char *pathname, int flags, int mode); 💖

const char *explain_open(const char *pathname, int flags, int mode);

explain_open is the one you call when you want an explanation of an error that the open(2) system call handed back to you. The least the message will contain is the value of strerror(errno), but honestly? Usually it does much better and points at the actual underlying cause, in more detail. It's giving forensic scientist 🔍

The errno global variable is the one used to obtain the error value that gets decoded.

This function is meant to be used in a fashion similar to this example, no cap:

int fd = open(pathname, flags, mode);
if (fd < 0)
{
    fprintf(stderr, '%s0, explain_open(pathname, flags, mode));
    exit(EXIT_FAILURE);
}

• pathname — the original pathname, exactly as passed to the open(2) system call.
• flags — the original flags, exactly as passed to the open(2) system call.
• mode — the original mode, exactly as passed to the open(2) system call (or zero if the original call didn't need a mode argument).

Returns: the message explaining the error. This message buffer is shared by all libexplain functions that don't supply a buffer in their argument list. It will be overwritten by the next call to any libexplain function that shares this buffer — and yes, including other threads. 😭

Note: this function is not thread safe, because it shares a return buffer across all threads, and so do many other functions in this library.

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🦋 explain_errno_open 🦋

const char *explain_errno_open(int errnum, const char *pathname, int flags, int mode);

explain_errno_open does the same iconic job: you get an explanation of an error returned by the open(2) system call. The least the message will contain is the value of strerror(errnum), but usually it does much better and shows you the underlying cause in more detail. periodt

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

int fd = open(pathname, flags, mode);
if (fd < 0)
{
    int err = errno;
    fprintf(stderr, '%s0, explain_errno_open(err, pathname,
        flags, mode));
    exit(EXIT_FAILURE);
}

• errnum — the error value to be decoded, usually grabbed from the errno global variable just before this function is called. You need to do it this way if you have to call any code between the system call being explained and this function, because many libc functions will alter the value of errno. Sneaky of them fr fr.
• pathname — the original pathname, exactly as passed to the open(2) system call.
• flags — the original flags, exactly as passed to the open(2) system call.
• mode — the original mode, exactly as passed to the open(2) system call (or zero if the original call didn't need a mode argument).

Returns: the message explaining the error. Same deal as before — this message buffer is shared by all libexplain functions which don't supply a buffer in their argument list, and it will be overwritten by the next call to any libexplain function that 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 too.

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🌸 explain_message_open 🌸

void explain_message_open(char *message, int message_size, const char *pathname, int flags, int mode);

explain_message_open gets you an explanation of an error returned by the open(2) system call. Least it'll contain is the value of strerror(errno), but usually it does much better and indicates the underlying cause in more detail. slay

The errno global variable is used to obtain the error value to be decoded.

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

int fd = open(pathname, flags, mode);
if (fd < 0)
{
    char message[3000];
    explain_message_open(message, sizeof(message), pathname, flags,
        mode);
    fprintf(stderr, '%s0, message);
    exit(EXIT_FAILURE);
}

• message — the location in which to store the returned message. And here's the glow-up: because a message return buffer has been 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 open(2) system call.
• flags — the original flags, exactly as passed to the open(2) system call.
• mode — the original mode, exactly as passed to the open(2) system call (or zero if the original call didn't need a mode argument).

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💜 explain_message_errno_open 💜

void explain_message_errno_open(char *message, int message_size, int errnum, const char *pathname, int flags, int mode);

explain_message_errno_open gives you an explanation of an error returned by the open(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. It's giving diagnostic excellence ✨

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

int fd = open(pathname, flags, mode);
if (fd < 0)
{
    int err = errno;
    char message[3000];
    explain_message_errno_open(message, sizeof(message), err, pathname,
        flags, mode);
    fprintf(stderr, '%s0, message);
    exit(EXIT_FAILURE);
}

• message — the location in which to store the returned message. Because a message return buffer has been 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. do not skip this step bestie 😤
• pathname — the original pathname, exactly as passed to the open(2) system call.
• flags — the original flags, exactly as passed to the open(2) system call.
• mode — the original mode, exactly as passed to the open(2) system call (or zero if the original call didn't need a mode argument).

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⭐ COPYRIGHT ⭐

• libexplain version 1.4
• Copyright (C) 2008 Peter Miller

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🫶 AUTHOR 🫶

Written by Peter Miller <pmiller@opensource.org.au>

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and that's the whole page, bestie 💖 that was explain_open(3), from libexplain version 1.4, with Copyright (C) 2008 Peter Miller. go forth and read your errnos with main character energy 🌈💅