d_drop(9)

📦 version 7.3.1, in nixpkgs unstable

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

okay so this is d_drop from the kernel API manual, and honestly? she's a little icon of unhashing. let's get into it 🫶

✨ NAME ✨

d_drop — drop a dentry. that's it, that's the whole name. short, sweet, devastating 💅

🌸 SYNOPSIS 🌸

void d_drop (struct dentry *dentry );

literally just call her with a dentry and she does the thing. no return value, no drama, void queen 👑

🎀 ARGUMENTS 🎀

  • dentry — the dentry you're dropping. this is the main character of the whole operation, so like... know which one you're passing in, bestie 🙈

🦋 DESCRIPTION 🦋

so what does d_drop actually do? she unhashes the entry from the parent dentry hashes, so that it won't be found through a VFS lookup any more. bye bye, searchability ✨

and ngl, this is different from deleting the dentry — don't get it twisted:

  • d_delete will try to mark the dentry negative if possible, giving a successful _negative_ lookup 😭
  • d_drop will just make the cache lookup fail 💀

two very different vibes, okay? one is "yes she's here but she's negative," the other is "she's not in the cache at all, good luck finding her."

d_drop is used mainly for stuff that wants to invalidate a dentry for some reason — think NFS timeouts or autofs deletes. like when things get stale and you gotta let the cache know 🍓

k now the important caveats, pay attention 🔥 __d_drop requires dentry->d_lock ___d_drop doesn't mark dentry as "unhashed" — dentry->d_hash.pprev will be LIST_POISON2, not NULL. so if you're out here checking for NULL to figure out hashed-ness, that check will NOT slay the way you think it will 💀

🌈 SEE ALSO 🌈

Kernel file ./fs/dcache.c — and here's the whole friend group, no cap, every single one:

and that's the page, bestie! go forth and unhash responsibly 💜

sign-off time 🎀 — this one lives under ./fs, dated <italic>October 2026</italic>, and it's filed as d_drop(9). mwah, ily, see u in the next manpage ✨

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