do_inode_permission(9)

📦 version 7.3.1, in nixpkgs unstable

💅 do_inode_permission(9) — from the Kernel API Manual, bestie

Okay so picture this: you're in the kernel, you need a permission check, and you want it fast. This is that function. Let's get into it 🫶

✨ NAME ✨

do_inode_permission — literally just UNIX permission checking, no cap 💅

🌸 SYNOPSIS 🌸

int do_inode_permission (struct mnt_idmap *idmap , struct inode *inode ,
       int mask );

Three args, one int back. Clean. Iconic. We love a signature that doesn't overstay its welcome ✨

🎀 ARGUMENTS 🎀

  • idmap — the idmap of the mount that this inode was found from. like, which mount family it belongs to, yk? 🦋
  • inode — the actual inode we're checking permissions on. this is the main character here 👑
  • mask — which right(s) you're checking for — think MAY_READ, MAY_WRITE, MAY_EXEC ... that whole squad 💫

💖 DESCRIPTION 💖

So here's the vibe: we _really_ want to just call generic_permission without even looking at the inode->i_op values. Like, why are we even checking, right? 🙈

The way we pull this off is by keeping a cache flag in inode->i_opflags that basically says:

"this has not special permission function, use the fast case" ⚡

Translation bestie: if that flag's set, we skip the whole investigation and go straight to the fast path. No detours, no drama, just speed 🏎️✨

🦋 SEE ALSO 🦋

Everything's in the kernel file ./fs/namei.c — here's the whole friend group, no one left out fr fr:

ngl bestie, if you're poking at i_opflags yourself, pls be careful — the fast case is only fast because that flag tells the truth 💀

🌈 and that's the page!! brought to you by ./fs, dated October 2026 — mwah, read it again whenever you forget how the fast path works 💜🎀

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