isc_register(9)

💅 isc_register — like, register an I/O interruption subclass, bestie

okay so welcome to isc_register(9) from the Kernel API Manual ✨ this is the little function that gets your I/O interruption subclass on the guest list 🎀 it's short, it's sweet, and it literally just does one thing — but we're gonna understand it fr fr.

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✨ SYNOPSIS ✨

void isc_register (unsigned int isc );

that's it. that's the whole vibe check. no return value (void, she gives nothing back and she's iconic for it 💅), one argument, and then she's done 🫶

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🦋 ARGUMENTS 🦋

• isc — the I/O interruption subclass you wanna register 🌸 like, this is the thing you're signing up. that's it, that's the whole argument.

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💖 DESCRIPTION 💖

okay so here's the tea ☕ — when you call isc_register, the number of users for isc goes up 📈. every time somebody calls it, the user count for that subclass just keeps climbing. no cap.

and the main character moment 👑: if you happen to be the first user to register isc, then the corresponding I/O interruption subclass mask gets enabled ✨. like you're the one who turns the lights on at the party. everybody after you just benefits from your slay 🎀

if you're not the first? no big deal, the count still goes up, the mask is already enabled, you just vibe in 🌈

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🚨 CONTEXT 🚨

🫶 read this part, bestie, it's important: this function must not be called in interrupt context. like, not optional, not "eh it'll probably be fine". just don't. 🙈

call it from normal context or the kernel will have opinions and you will Not have a good time 😭

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🧚 SEE ALSO 🧚

• Kernel file ./drivers/s390/cio/isc.c — go read the source, it's giving transparency 💜
• isc_unregister(9) — the nemesis, the counterpart, the one who takes names off the list ⭐

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so yeah, that's isc_register 🦋 register your subclass, bump the user count, maybe enable a mask, definitely don't do it in interrupt context, periodt 💅

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this little love letter came from the kernel source at ./drivers/s390/cio, dated October 2026, and it's filed under isc_register(9) in case you need to find it again 🌸 mwah, go forth and register responsibly 💖✨