lookup_fast(9)

💅 lookup_fast(9) — fast lockless (but racy) dentry lookup, bestie edition 💅

okay so this is the lookup_fast(9) kernel API manual page, and it's giving very "fast path but do not forget the vibes" energy ✨. No cap, every detail is still here.

🌸 NAME 🌸

• lookup_fast — do fast lockless (but racy) lookup of a dentry

✨ SYNOPSIS ✨

struct dentry * lookup_fast (struct nameidata *nd );

🎀 ARGUMENTS 🎀

• nd — current nameidata

🦋 DESCRIPTION 🦋

Do a fast, but racy lookup in the dcache for the given dentry, and revalidate it. Returns a valid dentry pointer or NULL if one wasn't found. On error, an ERR_PTR will be returned.

bestie, it's literally racy — the manual says so 💀

If this function returns a valid dentry and the walk is no longer lazy, the dentry will carry a reference that must later be put. If RCU mode is still in force, then this is not the case and the dentry must be legitimized before use. If this returns NULL, then the walk will no longer be in RCU mode.

💖 SEE ALSO 💖

Kernel file ./fs/namei.c and the whole friend group is tagged: check_acl(9), acl_permission_check(9), generic_permission(9), do_inode_permission(9), sb_permission(9), inode_permission(9), path_get(9), path_put(9), path_connected(9), try_to_unlazy(9), try_to_unlazy_next(9), complete_walk(9), may_follow_link(9), safe_hardlink_source(9), may_linkat(9), may_create_in_sticky(9), start_dirop(9), end_dirop(9), kern_path_parent(9), vfs_path_parent_lookup(9), vfs_path_lookup(9), try_lookup_noperm(9), lookup_noperm(9), lookup_one(9), lookup_one_unlocked(9), lookup_one_positive_killable(9), lookup_one_positive_unlocked(9), lookup_noperm_unlocked(9), start_creating(9), start_removing(9), start_creating_killable(9), start_removing_killable(9), start_creating_noperm(9), start_removing_noperm(9), start_creating_dentry(9), start_removing_dentry(9), __start_renaming(9), start_renaming(9), start_renaming_dentry(9), start_renaming_two_dentries(9), vfs_prepare_mode(9), vfs_create(9), atomic_open(9), vfs_lookup_open(9), vfs_tmpfile(9), kernel_tmpfile_open(9), end_creating_path(9), dentry_create(9), vfs_mknod(9), vfs_mkdir(9), vfs_rmdir(9), vfs_unlink(9), vfs_symlink(9), vfs_link(9), vfs_rename(9), vfs_readlink(9), vfs_get_link(9), page_get_link(9), page_put_link(9).

sign-off bestie 🫶: source ./fs, dated October 2026, manual lookup_fast(9) — mwah 💋✨