explain_eventfd(3)

💖 explain_eventfd — ok bestie, let's talk about why your eventfd(2) call is crying 💖

So this is a page from the Library Functions Manual, and its whole entire job is to explain the errors that eventfd(2) hands you. Yes queen, it's explain_eventfd(3). Sit down, hydrate, let's go. 🫶

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✨ NAME ✨

explain_eventfd — explain eventfd(2) errors

Like. That's it. That's the whole vibe. It explains the errors. Iconic behaviour, honestly. 💅

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🌸 SYNOPSIS 🌸

#include <libexplain/eventfd.h>
const char *explain_eventfd(unsigned int initval, int flags);
const char *explain_errno_eventfd(int errnum, unsigned int initval, int
flags);
void explain_message_eventfd(char *message, int message_size, unsigned
int initval, int flags);
void explain_message_errno_eventfd(char *message, int message_size, int
errnum, unsigned int initval, int flags);

Four functions. Four besties. Each one has a slightly different job and we're gonna give each one their moment, no skipping, no cap. ✨

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🦋 DESCRIPTION 🦋

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

Translation: when eventfd(2) says "nope 😭" and sets errno, these little guys turn that cryptic number into an actual sentence you can read with your own two eyeballs. Groundbreaking. Life-changing. Slay. 🔥

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💜 explain_eventfd

const char *explain_eventfd(unsigned int initval, int flags);

The explain_eventfd function is used to obtain an explanation of an error returned by the eventfd(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.

• initval — The original initval, exactly as passed to the eventfd(2) system call.
• flags — The original flags, exactly as passed to the eventfd(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. 🚨 Like, read that again, bestie. Shared buffer. All threads. It WILL get overwritten. 🚨

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

int result = eventfd(initval, flags);
if (result < 0)
{
    fprintf(stderr, "%s\n", explain_eventfd(initval, flags));
    exit(EXIT_FAILURE);
}

The above code example is available pre‐packaged as the explain_eventfd_or_die(3) function. 🎀 (yes, "or die" is the function name, and yes, it's exactly as dramatic as it sounds.)

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🎀 explain_errno_eventfd

const char *explain_errno_eventfd(int errnum, unsigned int initval, int
flags);

The explain_errno_eventfd function is used to obtain an explanation of an error returned by the eventfd(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. 😤 yes, other functions will absolutely stomp on your errno, so save it first. Character development.
• initval — The original initval, exactly as passed to the eventfd(2) system call.
• flags — The original flags, exactly as passed to the eventfd(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. 💀 Same warning, same energy. Not a drill.

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

int result = eventfd(initval, flags);
if (result < 0)
{
    int err = errno;
    fprintf(stderr, "%s\n", explain_errno_eventfd(err, initval,
    flags));
    exit(EXIT_FAILURE);
}

The above code example is available pre‐packaged as the explain_eventfd_or_die(3) function. ✨

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🌈 explain_message_eventfd

void explain_message_eventfd(char *message, int message_size, unsigned
int initval, int flags);

The explain_message_eventfd function is used to obtain an explanation of an error returned by the eventfd(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 look, self-care! You brought your own buffer, you get thread safety. Main character energy.
• message_size — The size in bytes of the location in which to store the returned message.
• initval — The original initval, exactly as passed to the eventfd(2) system call.
• flags — The original flags, exactly as passed to the eventfd(2) system call.

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

int result = eventfd(initval, flags);
if (result < 0)
{
    char message[3000];
    explain_message_eventfd(message, sizeof(message), initval,
    flags);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

The above code example is available pre‐packaged as the explain_eventfd_or_die(3) function. 💖

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🧚 explain_message_errno_eventfd

void explain_message_errno_eventfd(char *message, int message_size, int
errnum, unsigned int initval, int flags);

The explain_message_errno_eventfd function is used to obtain an explanation of an error returned by the eventfd(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. 🫶 bestie brought her own buffer, bestie is 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. 😭 seriously, grab it before anything else touches it.
• initval — The original initval, exactly as passed to the eventfd(2) system call.
• flags — The original flags, exactly as passed to the eventfd(2) system call.

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

int result = eventfd(initval, flags);
if (result < 0)
{
    int err = errno;
    char message[3000];
    explain_message_errno_eventfd(message, sizeof(message), err,
    initval, flags);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

The above code example is available pre‐packaged as the explain_eventfd_or_die(3) function. ⭐

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👑 SEE ALSO 👑

• eventfd(2) — create a file descriptor for event notification
• explain_eventfd_or_die(3) — create a file descriptor for event notification and report errors

(go read those too, iykyk 🦋)

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💅 COPYRIGHT 💅

• libexplain version 1.4
• Copyright (C) 2009 Peter Miller

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ok that's the whole page, you're all caught up, go forth and let your error messages be verbose for once. no cap, that's the entire point of this library. 🌸

— written for the Library Functions Manual, the explain_eventfd(3) page itself, libexplain version 1.4, Copyright (C) 2009 Peter Miller. mwah, love u, bye 💖