MODULE(9)

✨ MODULE(9) ✨

okay bestie, this is the section 9 page about module — the struct that describes a kernel module. it's from the Kernel Developer's Manual, so grab your iced coffee and let's get into it 🫶

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💅 NAME 💅

module — the structure that describes a kernel module ✨

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🌸 DESCRIPTION 🌸

so every module in the kernel is described by a module_t structure. what's in it? the name of the device, a unique ID number, a pointer to an event handler function, and a pointer to an argument that gets handed to that event handler — plus some kernel internal data. ngl there's a lot going on in there.

and if the event handler function is NULL? no problem, the module just uses a no-operation function handler instead. easy. 💅

the DECLARE_MODULE(9) macro is what registers the module with the system. that's the main character move. 👑

when the module is loaded, the event handler function gets called with the what argument set to MOD_LOAD. okay so far so good.

on unload it's first called with what set to MOD_QUIESCE. here's the tea: if the unload wasn't forced, a non-zero return will prevent the unload from happening. so return non-zero if you're not ready to leave, periodt. ✋

if the unload continues, what is set to MOD_UNLOAD. and if the module returns non-zero to this one? the unload will not happen. simple as that.

now this is the part everyone gets confused about, so listen up 🍓 — the difference between MOD_QUIESCE and MOD_UNLOAD:

• the module should fail MOD_QUIESCE if it is currently in use
• whereas MOD_UNLOAD should only fail if it is impossible to unload the module — for instance, because there are memory references to the module which cannot be revoked

like, in-use vs. literally-cannot-let-go. different vibes entirely. 💀

when the system is shutting down, what contains the value of MOD_SHUTDOWN. yeah, that happens too.

and for unsupported and unrecognized values of what? the module should return EOPNOTSUPP. that's it, that's the answer. 🎀

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🦋 EXAMPLES 🦋

here's the whole thing in action, and yes you can copy it exactly:

#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/module.h>

static int foo_handler(module_t mod, int /*modeventtype_t*/ what,
                       void *arg);

static moduledata_t mod_data= {
        "foo",
        foo_handler,
        NULL
};

MODULE_VERSION(foo, 1);
MODULE_DEPEND(foo, bar, 1, 3, 4);

DECLARE_MODULE(foo, mod_data, SI_SUB_EXEC, SI_ORDER_ANY);

iconic. ate. no notes. 🔥

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🌈 SEE ALSO 🌈

• DECLARE_MODULE(9)
• DEV_MODULE(9)
• DRIVER_MODULE(9)
• MODULE_DEPEND(9)
• MODULE_PNP_INFO(9)
• MODULE_VERSION(9)
• SYSCALL_MODULE(9)
• /usr/share/examples/kld

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💜 AUTHORS 💜

This manual page was written by Alexander Langer <alex@FreeBSD.org>.

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that's the whole page bestie, go forth and load some modules 💖🦋✨

— this one's from the Debian crew, dated November 11, 2021 (the version is right there in the footer, iykyk) 🎀