VM_MAP_LOCK(9)

💖 VM_MAP_LOCK — vm_map locking macros 💖

okay bestie, sit DOWN, because we're talking about vm_map_lock and its whole friend group — and yes, this is from the Kernel Developer's Manual, section 9, so you already know it's giving big-kid kernel energy. 🧚✨

The squad is: vm_map_lock, vm_map_unlock, vm_map_lock_read, vm_map_unlock_read, vm_map_trylock, vm_map_trylock_read, vm_map_lock_upgrade, vm_map_lock_downgrade — the vm_map locking macros. Eight little icons. All of them. Periodt. 👑

✨ SYNOPSIS ✨

first things first, you gotta bring in the essentials, no skipping:

#include <sys/param.h>
#include <vm/vm.h>
#include <vm/vm_map.h>

then it's just:

void
vm_map_lock(vm_map_t map);

void
vm_map_unlock(vm_map_t map);

void
vm_map_lock_read(vm_map_t map);

void
vm_map_unlock_read(vm_map_t map);

int
vm_map_trylock(vm_map_t map);

int
vm_map_trylock_read(vm_map_t map);

int
vm_map_lock_upgrade(vm_map_t map);

int
vm_map_lock_downgrade(vm_map_t map);

look at that. gorgeous. no notes. 💅

🌸 DESCRIPTION 🌸

so here's the tea on each one, bestie, one by one:

• vm_map_lock() — this macro grabs an exclusive lock on map. it's the main character lock, nobody else gets in while it's held. 🫶
• vm_map_unlock() — releases that exclusive lock on map. bye babe, thanks for coming. 💖
• vm_map_lock_read() — this one gets a read-lock on map. like, you can look, but don't touch. 👀
• vm_map_unlock_read() — releases the read-lock on map. lookin' time is over. 🎀
• vm_map_trylock() — tries to snag an exclusive lock on map, but it's not gonna wait around for it. if the lock can't be acquired immediately it returns FALSE; otherwise it returns TRUE with the lock acquired. lowkey impatient, highkey efficient. 😌
• vm_map_trylock_read() — same vibe but for a read-lock on map. returns FALSE if the lock can't be acquired immediately; otherwise returns TRUE with the lock acquired. no waiting, no begging. ✨
• vm_map_lock_upgrade() — attempts to atomically upgrade a read-lock on map to an exclusive lock. glow-up but make it atomic. 🦋
• vm_map_lock_downgrade() — attempts to downgrade an exclusive lock on map to a read-lock. sometimes you just gotta step back and let the read-locks breathe. 🌈

🛠️ IMPLEMENTATION NOTES 🛠️

as of right now, bestie, all of these locking macros implement their locks as sleep locks. every single one. that's the whole note. fr fr. 💀

👀 SEE ALSO 👀

• vm_map(9) — go read it, it's the source material, iykyk. 📚

👑 AUTHORS 👑

this manual page was written by Bruce M Simpson <bms@spc.org>. king behavior, honestly. 🫡

aaaand that's the whole page, bestie!! this one came from Debian, dated July 19, 2003 — vintage but still slaying. go lock your maps responsibly, mwah 💋💖✨