NULLOP(9)

💅 NULLOP(9) — like, the kernel's built-in do nothing squad

okay bestie so this is a Kernel Developer's Manual page, section 9, and it's literally about functions that do absolutely nothing (or fail on purpose). no cap, that's the whole vibe. 🎀

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✨ NAME ✨

nullop — dummy functions 🫶

🌸 SYNOPSIS 🌸

#include <sys/systm.h>

int
nullop(void *v);

void
voidop(void);

int
enodev(void);

int
enxio(void);

int
enoioctl(void);

int
enosys(void);

int
eopnotsupp(void);

🦋 DESCRIPTION 🦋

k so, nullop() is the original "null operation" — a generic one. it always returns the value 0. that's it. that's the whole job. iconic honestly. ✨

voidop() takes no arguments and does nothing. queen of minding her own business 💅

and then we have the fail squad — enodev(), enxio(), enoioctl(), enosys(), and eopnotsupp(). these always fail, and they return ENODEV, ENXIO, ENOTTY, ENOSYS, and EOPNOTSUPP, respectively. yes, in that exact order, don't mix them up bestie 😭

ngl the mapping is the whole point: enoioctl() hands back ENOTTY (not ENOIOCTL, which isn't a thing), so keep your eyes on that one 🙈

🔥 EXAMPLES 🔥

here's a case where nullop() genuinely comes in clutch:

uint64_t xc;

...

xc = xc_broadcast(0, (xcfunc_t)nullop, NULL, NULL);
xc_wait(xc);

like, you need a function pointer and you've got nothing to actually do? boom. nullop. main character energy 👑

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💖 that's the whole page babes 💖 this is from the Debian edition, dated July 25, 2010 — vintage, honestly. go forth and return 0 🧚‍♀️🌸