diag204(9)

💫 diag204 💫

okay so bestie, welcome to the diag204(9) page from the Kernel API Manual — yes we're in kernel-land, yes it's s390, and yes it's giving big main character energy 🎀 this one's short and sweet, so let's get into it ✨

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🌸 NAME 🌸

diag204 — literally just: issue the diagnose 204 call. that's it. that's the whole vibe 💅

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🦋 SYNOPSIS 🦋

int diag204 (unsigned long subcode , unsigned long size , void *addr );

like, three args, one int back. no cap, that's the whole signature 🙈

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🎀 ARGUMENTS 🎀

• subcode — the subcode of diagnose 204 that you actually want to run ✨ whichever one you pick, that's the one that gets executed.
• size — the size of the area, measured in pages, that addr points to — but only if addr is actually given, iykyk 🫶.
• addr — the memory area (it's a vmalloc'ed one!) where the result gets written 💖.

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💜 DESCRIPTION 💜

so the whole thing is: execute diagnose 204 with the subcode you handed it, and write the result into the memory area you specified with addr. iconic, honestly 👑

but listen — the details matter, bestie, don't skip them:

⚠️ for subcodes that don't write a result to memory, both size and addr must be zero. not "should", must. zero. both of them. no exceptions 🔥

and if you do specify addr, it has two strict requirements, fr fr:

• it must be page aligned 📐
• it must have been allocated with vmalloc 🧚

the good news? if a conversion to real / physical addresses is required, this function handles that for you — you don't have to do it yourself, it's already slaying that job 💅✨

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🌈 SEE ALSO 🌈

• Kernel file ./arch/s390/kernel/diag/diag.c — go read the source, bestie, it's right there 📖💖

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and that's a wrap, cutie 🫶 this page came to you from ./arch/s390/kernel/diag, dated October 2026 — go forth and diagnose responsibly, mwah 💋🌸