fscache_write_to_cache(9)

📦 version 7.3.1, in nixpkgs unstable

💾 fscache_write_to_cache — the kernel API manual page, bestie edition

okay so this is fscache_write_to_cache(9), straight out of the Kernel API Manual, and it's genuinely one of those functions that sounds scary but is lowkey just "pls put my dirty data in the cache, thanks 🫶". Buckle up, we're going in ✨

✨ NAME ✨

fscache_write_to_cache — save a write to the cache and clear PG_fscache 💅

🎀 SYNOPSIS 🎀

void fscache_write_to_cache (struct fscache_cookie *cookie , struct
       address_space *mapping , loff_t start , size_t len , loff_t i_size ,
       netfs_io_terminated_t term_func , void *term_func_priv , bool
       using_pgpriv2 , bool caching );

it's giving "lots of arguments, but every single one is doing her job 👑" — eight of them, no cap, and every one matters.

🦋 ARGUMENTS 🦋

  • cookie — the cookie that represents the cache object 🍪 (yes, it's literally called a cookie, slay)
  • mapping — the netfs inode you're using as the source
  • start — where in mapping this whole thing kicks off
  • len — the amount of data to write back
  • i_size — the new size of the inode
  • term_func — the function that gets called once it's all done
  • term_func_priv — the private data for term_func 🙈
  • using_pgpriv2 — whether we're using PG_private_2 to mark an in-progress write
  • caching — whether we actually want to do the caching (yes, that's the whole vibe check right there ⭐)

🌸 DESCRIPTION 🌸

So this is a helper function for a netfs — it takes dirty data from an inode and writes it into the cache object that's backing it. literally its whole purpose 💖

start and len describe the range of the data. and listen, this does not need to be page-aligned — but to satisfy DIO requirements, the cache may expand it up to the page boundaries on either end. so it can grow a lil bit on each side, ngl 🔥

All the pages covering the range must be marked with PG_fscache. non-negotiable, bestie 🙏

If it's given, term_func will be called upon completion and supplied with term_func_priv. and heads up 🚨 — if using_pgpriv2 is set, the PG_private_2 flags will have been cleared by this point, so the netfs must retain its own pin on the mapping. don't sleep on that one, fr fr 😭

🧚 SEE ALSO 🧚

Kernel file ./include/linux/fscache.h — and the whole friend group 💜:

like, the whole fscache cinematic universe 🌈 go read them, iykyk 👑

and that's the page!! mwah 💋 source/version lives over in ./include/linux, dated October 2026, and this whole glittery thing is filed under fscache_write_to_cache(9) — go forth and cache responsibly, bestie 🌸✨🎀

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