luo_preserve_file(9)

💅 luo_preserve_file(9) — the Kernel API Manual glow-up 🎀

okay so bestie, welcome to the luo_preserve_file(9) page. yes, that's the whole manual name, it's giving very "kernel api manual" energy and honestly? iconic. let's get into it ✨

---

🌸 NAME 🌸

luo_preserve_file — like, the actual start of preserving a file descriptor. the opening act. the main character entrance. 💫

---

🦋 SYNOPSIS 🦋

int luo_preserve_file (struct luo_file_set *file_set , u64 token , int
fd );

yes the line break is real, that's literally how it's written, no cap 💀

---

💖 ARGUMENTS 💖

• file_set — the file_set bestie that the preserved file is gonna get added to. it's the group chat the file joins. 🫶
• token — a unique, user-provided identifier for the file. you make it, you own it, it's your little name tag. 🏷️
• fd — the actual file descriptor being preserved. the star of the show. 🌟

---

✨ DESCRIPTION ✨

so this function orchestrates (fancy word, love that for her) the first phase of preserving a file. on entry it grabs a reference to the 'struct file' via fget, which lowkey makes LUO a co-owner of the file. and she holds that reference until the file is either unpreserved or successfully finished in the next kernel — so the file literally cannot get prematurely destroyed. protective queen behavior honestly 👑

and like, the whole first-phase-preserving deal goes down in these steps:

1. Validates that the token isn't already in use inside the file_set. no duplicate names in this house 🚫
2. Ensures the file_set's memory for files serialization is allocated (and allocates it if needed). if it's not there, she builds it. self-sufficient 💅
3. Iterates through the registered handlers, calling can_preserve on each to find one that's compatible with the given fd. it's giving speed dating but for handlers 💘
4. Calls the handler's .preserve operation, which saves the file's state and hands back an opaque private data handle. mysterious. we love a little mystery 🎭
5. Adds the new instance to the file_set's internal list. welcome to the club, babes 💌

on success, LUO takes a reference to the 'struct file' and straight up considers it under her management until it's unpreserved or finished. she's responsible for it now, that's her child 🥹

and if anything fails? she cleans up all the intermediate allocations (the file reference, the memory for the 'luo_file' struct, all of it, every crumb 🧹) before returning an error. no mess left behind, periodt.

---

🌈 CONTEXT 🌈

Can be called from an ioctl handler during normal system operation. so like, just normal everyday vibes. nothing chaotic. 🧚

---

🔥 RETURN 🔥

0 on success — slay! ✨

and returns a negative errno on failure:

• -EEXIST — if the token is already used. taken, bestie, sorry 💀
• -EBUSY — if the file descriptor is already preserved by another session. she's booked and busy 🚫
• -EBADF — if the file descriptor is invalid. not a real fd, bestie 😭
• -ENOSPC — if the file_set is full. no room, we're at capacity 🙈
• -ENOENT — if no compatible handler is found. nobody showed up to the function 💔
• -ENOMEM — on memory allocation failure. the allocator said no 🫠
• Other errors might be returned by .preserve. anything could happen, iykyk 🎲

---

👑 SEE ALSO 👑

Kernel file ./kernel/liveupdate/luo_file.c, LUO File Descriptors(9), struct luo_file(9), luo_file_unpreserve_files(9), luo_file_freeze(9), luo_file_unfreeze(9), luo_retrieve_file(9), luo_file_finish(9), luo_file_deserialize(9), liveupdate_register_file_handler(9), liveupdate_unregister_file_handler(9) — go read those next, bestie, the whole cinematic universe is right there 📚🦋

---

and that's the page! 💜 source: ./kernel/liveupdate · date: October 2026 · mwah, love u, go preserve some files 💅✨🎀