calipso_genopt(9)

📦 version 7.3.1, in nixpkgs unstable

💅 calipso_genopt(9) — the Kernel API Manual, but make it cute

okay so bestie, welcome to calipso_genopt(9), a page from the Kernel API Manual, and it's literally about generating a CALIPSO option. That's the whole vibe. Let's get into it ✨

✨ NAME ✨

calipso_genopt — Generate a CALIPSO option 🎀

🌸 SYNOPSIS 🌸

Ngl the signature is a whole mood, so here it is verbatim, no cap:

int calipso_genopt (unsigned char *buf , u32 start , u32 buf_len , const
struct calipso_doi *doi_def , const struct netlbl_lsm_secattr *secattr
);

🦋 ARGUMENTS 🦋

Okay so these are the five besties you're handing to this function. Know them, love them:

  • buf — the option buffer. It's the canvas, the stage, the main character. 💖
  • start — the offset from which to write. Like where the pen first touches the paper ✍️
  • buf_len — the size of opt_buf. Yes, the manpage literally says opt_buf — that's the name it uses, so we're keeping it exactly like that, periodt. 🫶
  • doi_def — the CALIPSO DOI to use. The chosen one 👑
  • secattr — the security attributes. The lore, the backstory 🧚

🔥 DESCRIPTION 🔥

So what does it do?? It generates a CALIPSO option using the DOI definition and the security attributes you passed to the function. Iconic behaviour honestly.

But wait, there's more — it also generates upto three bytes of leading padding, and that padding is the thing that ensures the option is 4n + 2 aligned. The way that alignment just works 😭✨

And then it returns the number of bytes written, which includes any initial padding. So the return value is your lil receipt for the whole operation 🧾💅

👑 SEE ALSO 👑

Okay this list is long but we do not skip a single one, because every soul here matters. First up, the kernel file:

./net/ipv6/calipso.c

And now the whole squad, in order, no one left behind:

bestie reminder: the return value counts the padding too, so don't come for the byte count and act surprised. 🙈

and that's the page!! mwah 💋 signed off from ./net/ipv6, dated October 2026, and yes the footer says calipso_genopt(9) because we always bring it back to where we started 🎀✨🫶

📦 where this page comes from