Function vm_map_find

freebsd/vm/vm_map.c:2123–2267

* vm_map_find finds an unallocated region in the target address * map with the given length. The search is defined to be * first-fit from the specified address; the region found is * returned in the same parameter. * * If object is non-NULL, ref count must be bumped by caller * prior to making call to account for the new entry. */

 *	prior to making call to account for the new entry.
 */
int
vm_map_find(vm_map_t map, vm_object_t object, vm_ooffset_t offset,
	    vm_offset_t *addr,	/* IN/OUT */
	    vm_size_t length, vm_offset_t max_addr, int find_space,
	    vm_prot_t prot, vm_prot_t max, int cow)
{
	vm_offset_t alignment, curr_min_addr, min_addr;
	int gap, pidx, rv, try;
	bool cluster, en_aslr, update_anon;

	KASSERT((cow & (MAP_STACK_GROWS_DOWN | MAP_STACK_GROWS_UP)) == 0 ||
	    object == NULL,
	    ("vm_map_find: non-NULL backing object for stack"));
	MPASS((cow & MAP_REMAP) == 0 || (find_space == VMFS_NO_SPACE &&
	    (cow & (MAP_STACK_GROWS_DOWN | MAP_STACK_GROWS_UP)) == 0));
	if (find_space == VMFS_OPTIMAL_SPACE && (object == NULL ||
	    (object->flags & OBJ_COLORED) == 0))
		find_space = VMFS_ANY_SPACE;
	if (find_space >> 8 != 0) {
		KASSERT((find_space & 0xff) == 0, ("bad VMFS flags"));
		alignment = (vm_offset_t)1 << (find_space >> 8);
	} else
		alignment = 0;
	en_aslr = (map->flags & MAP_ASLR) != 0;
	update_anon = cluster = clustering_anon_allowed(*addr) &&
	    (map->flags & MAP_IS_SUB_MAP) == 0 && max_addr == 0 &&
	    find_space != VMFS_NO_SPACE && object == NULL &&
	    (cow & (MAP_INHERIT_SHARE | MAP_STACK_GROWS_UP |
	    MAP_STACK_GROWS_DOWN)) == 0 && prot != PROT_NONE;
	curr_min_addr = min_addr = *addr;
	if (en_aslr && min_addr == 0 && !cluster &&
	    find_space != VMFS_NO_SPACE &&
	    (map->flags & MAP_ASLR_IGNSTART) != 0)
		curr_min_addr = min_addr = vm_map_min(map);
	try = 0;
	vm_map_lock(map);
	if (cluster) {
		curr_min_addr = map->anon_loc;
		if (curr_min_addr == 0)
			cluster = false;
	}
	if (find_space != VMFS_NO_SPACE) {
		KASSERT(find_space == VMFS_ANY_SPACE ||
		    find_space == VMFS_OPTIMAL_SPACE ||
		    find_space == VMFS_SUPER_SPACE ||
		    alignment != 0, ("unexpected VMFS flag"));
again:
		/*
		 * When creating an anonymous mapping, try clustering
		 * with an existing anonymous mapping first.
		 *
		 * We make up to two attempts to find address space
		 * for a given find_space value. The first attempt may
		 * apply randomization or may cluster with an existing
		 * anonymous mapping. If this first attempt fails,
		 * perform a first-fit search of the available address
		 * space.
		 *