VM_MAP_LOOKUP(9)

💅 VM_MAP_LOOKUP(9) 💅

okay bestie, welcome to the Kernel Developer's Manual page for vm_map_lookup and vm_map_lookup_done — the little duo that helps you look up the vm_object backing a given virtual region. it’s giving kernel-internals main character energy, and we’re gonna get through it together 🫶✨

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🎀 NAME 🎀

vm_map_lookup, vm_map_lookup_done — lookup the vm_object backing a given virtual region 💖

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✨ SYNOPSIS ✨

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

int
vm_map_lookup(vm_map_t *var_map, vm_offset_t vaddr,
    vm_prot_t fault_type, vm_map_entry_t *out_entry,
    vm_object_t *object, vm_pindex_t *pindex, vm_prot_t *out_prot,
    boolean_t *wired);

void
vm_map_lookup_done(vm_map_t map, vm_map_entry_t entry);

no cap, those includes and signatures are literally copy-pasted from the source of truth, so keep them exactly like that 🔥

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🌸 DESCRIPTION 🌸

so vm_map_lookup() is the function that attempts to find the vm_object, page index and protection for the given virtual address vaddr, in the map var_map — assuming a page fault of the type fault_type had occurred. it’s basically doing the “what’s behind this virtual address?” detective work 🔍💅

and this part is important, bestie: the return values are guaranteed until vm_map_lookup_done() is called to release the lock. so don’t go acting brand new and forget the cleanup, okay? 😭✨

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🦋 IMPLEMENTATION NOTES 🦋

not me spilling the lock tea: vm_map_lookup() acquires a read-lock on the map *var_map, but it does not release it. the caller should invoke vm_map_lookup_done() in order to release this lock. that’s the whole vibe — lookup first, then done to release the lock, periodt 🫶🔐

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💜 RETURN VALUES 💜

the vm_map_lookup() function returns KERN_SUCCESS, and sets the *object, *pindex, *out_prot, and *out_entry arguments appropriately for the hypothetical page fault. slay, that’s the success path ✨👑

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🌈 SEE ALSO 🌈

• vm_map(9)

go read that one too, iykyk 📚💖

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🎀 AUTHORS 🎀

this manual page was written by Bruce M Simpson <bms@spc.org>. iconic behavior, honestly 💅✨

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this cutie comes from the Debian manual pages, dated July 19, 2003 — mwah, xoxo 💋🎀