make_vfsuid(9)

📦 version 7.3.1, in nixpkgs unstable

💅 make_vfsuid(9) — the Kernel API Manual, bestie edition 🦋

okay so real talk, this is a page from the Kernel API Manual and honestly? it's a little icon and you're gonna get it in like two seconds. let's go ✨

✨ NAME ✨

make_vfsuid — maps a filesystem kuid according to an idmapping 🎀

🌸 SYNOPSIS 🌸

vfsuid_t make_vfsuid (struct mnt_idmap *idmap , struct user_namespace
*fs_userns , kuid_t kuid );

like, yes, the line break is doing its own thing, copy it exactly, no cap 💅

🦋 ARGUMENTS 🦋

  • idmap — the mount's idmapping. that's the whole vibe of this one.
  • fs_userns — the filesystem's idmapping. yes it also gets an idmap, they're matching ✨
  • kuid — the kuid to be mapped. that's the lil guy we're remapping 🥺

💖 DESCRIPTION 💖

So here's the tea: you take a kuid and you remap it from fs_userns into idmap. that's it, that's the function. 👑

Use this function when you're preparing a kuid to be reported to userspace. that's literally its whole job, bestie. it's giving middle-management-for-uids energy but like, in a good way 💀

now the fun part, the shortcuts 🌈:

  • If initial_idmapping determines that this is not an idmapped mount, we can simply return kuid unchanged. no work, no drama, we just hand it back 🫶
  • If initial_idmapping tells us that the filesystem is not mounted with an idmapping, we know the value of kuid won't change when calling from_kuid — so we can simply retrieve the value via __kuid_val directly. efficient queen behavior ⭐

🔥 RETURN 🔥

returns the kuid mapped according to idmap. slay.

but heads up 🙈 — if kuid has no mapping in either idmap or fs_userns, you get INVALID_UID back. that's the "no thoughts, head empty" result. don't say I didn't warn you 💀

👑 SEE ALSO 👑

the whole friend group, all linked, all iconic 💜

and that's the page!! this one lives at ./fs, stamped October 2026, and it's literally the make_vfsuid(9) page from the Kernel API Manual — go read the friends, mwah 🍓🧚✨

📦 where this page comes from