vfs_test_lock(9)

📦 version 7.3.1, in nixpkgs unstable

💅 vfs_test_lock — Kernel API Manual ✨

okay so bestie, today we're learning about vfs_test_lock(9). it's giving "peek at the lock without touching it" energy and honestly? iconic. 🎀

🌸 NAME 🌸

vfs_test_lock — test file byte range lock 🔒✨

🦋 SYNOPSIS 🦋

int vfs_test_lock (struct file *filp , struct file_lock *fl );

💖 ARGUMENTS 💖

  • filp — the file you wanna test the lock on, periodt 🫶
  • fl — the byte-range in the file you're testing; it also gets used to hold the result, so it's like doing double duty (main character energy fr fr) 💅

🌈 DESCRIPTION 🌈

okay so on entry, fl does not contain a lock — like, it's empty, it's just vibing and holding a description. it identifies a range (fl_start, fl_end) in the file (c.flc_file), plus an owner (c.flc_owner) for whom existing locks should be ignored 🙈. also c.flc_type and c.flc_flags are ignored — literally not important, don't even worry about them bestie 💀.

both fl_lmops and fl_ops in fl must be NULL. no cap. ⭐

it returns -ERRNO on failure 😭. and it shows there's a conflicting lock by setting fl->fl_type to something other than F_UNLCK — that's the little tell, iykyk 👑

🚨 big sister warning 🚨: if vfs_test_lock does find a lock and return it, the caller must use locks_free_lock or locks_release_private on the returned lock. like, you have to, it's not optional, don't leave it hanging 🫥💜

🔥 SEE ALSO 🔥

kernel file ./fs/locks.c plus this whole squad right here 👇 (besties, all of them):

✨💅 and that's the whole page, bestie! it's from the ./fs source, dated October 2026, page name vfs_test_lock(9) — slay, go test some locks responsibly 🎀🦋💖

📦 where this page comes from