VM_MAP_FIND(9)

📦 version 15.1, in freebsd 14.5, freebsd 15.1, nixpkgs unstable

✨ VM_MAP_FIND(9) ✨

okay so bestie, welcome to the VM_MAP_FIND(9) page — yes, that's the Kernel Developer's Manual, and yes we're gonna make it make sense. This is all about vm_map_find: finding a free region inside a map, and optionally mapping a vm_object. iykyk 🫶

🎀 NAME 🎀

vm_map_find — find a free region within a map, and optionally map a vm_object

🌸 SYNOPSIS 🌸

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

       int
       vm_map_find(vm_map_t map, vm_object_t object, vm_ooffset_t offset,
           vm_offset_t *addr, vm_size_t length, vm_offset_t max_addr,
           int find_space, vm_prot_t prot, vm_prot_t max, int cow);

🦋 DESCRIPTION 🦋

The vm_map_find() function attempts to find a free region in the target map, with the given length. If a free region is found, vm_map_find() creates a mapping of object via a call to vm_map_insert(9).

The arguments offset, prot, max, and cow are passed unchanged to vm_map_insert(9) when creating the mapping, if and only if a free region is found.

⚠️ bestie, important: if object is non-NULL, the reference count on the object must be incremented by the caller before calling this function to account for the new entry. no cap, do not skip that.

If max_addr is non-zero, it specifies an upper bound on the mapping. The mapping will only succeed if a free region can be found that resides entirely below max_addr.

The find_space argument specifies the strategy to use when searching for a free region of the requested length. For all values other than VMFS_NO_SPACE, vm_map_findspace(9) is called to locate a free region of the requested length with a starting address at or above *addr. The following strategies are supported:

🎯 the find_space strategy menu 🎯

  • VMFS_NO_SPACE — The mapping will only succeed if there is a free region of the requested length at the given address *addr.
  • VMFS_ANY_SPACE — The mapping will succeed as long as there is a free region.
  • VMFS_SUPER_SPACE — The mapping will succeed as long as there is a free region that begins on a superpage boundary. If object is non-NULL and is already backed by superpages, then the mapping will require a free region that aligns relative to the existing superpages rather than one beginning on a superpage boundary.
  • VMFS_OPTIMAL_SPACE — The mapping will succeed as long as there is a free region. However, if object is non-NULL and is already backed by superpages, this strategy will attempt to find a free region aligned relative to the existing superpages.
  • VMFS_ALIGNED_SPACE(n) — The mapping will succeed as long as there is a free region that aligns on a 2^n boundary.

🧚 IMPLEMENTATION NOTES 🧚

This function acquires a lock on map by calling vm_map_lock(9), and holds it until the function returns. 🔒

The search for a free region is defined to be first-fit, from the address addr onwards.

💀 RETURN VALUES 💀

The vm_map_find() function returns KERN_SUCCESS if the mapping was successfully created.

If space could not be found or find_space was VMFS_NO_SPACE and the given address, addr, was already mapped, KERN_NO_SPACE will be returned.

If the discovered range turned out to be bogus, KERN_INVALID_ADDRESS will be returned.

🌈 SEE ALSO 🌈

👑 AUTHORS 👑

This manual page was written by Bruce M Simpson <bms@spc.org>.

mwah 💋 that's the whole page — from Debian, dated September 12, 2013, under the VM_MAP_FIND(9) banner. slay, bye bestie! 🎀✨

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