Function vm_map_madvise

freebsd/vm/vm_map.c:2948–3136

* vm_map_madvise: * * This routine traverses a processes map handling the madvise * system call. Advisories are classified as either those effecting * the vm_map_entry structure, or those effecting the underlying * objects. */

 *	objects.
 */
int
vm_map_madvise(
	vm_map_t map,
	vm_offset_t start,
	vm_offset_t end,
	int behav)
{
	vm_map_entry_t entry, prev_entry;
	int rv;
	bool modify_map;

	/*
	 * Some madvise calls directly modify the vm_map_entry, in which case
	 * we need to use an exclusive lock on the map and we need to perform
	 * various clipping operations.  Otherwise we only need a read-lock
	 * on the map.
	 */
	switch(behav) {
	case MADV_NORMAL:
	case MADV_SEQUENTIAL:
	case MADV_RANDOM:
	case MADV_NOSYNC:
	case MADV_AUTOSYNC:
	case MADV_NOCORE:
	case MADV_CORE:
		if (start == end)
			return (0);
		modify_map = true;
		vm_map_lock(map);
		break;
	case MADV_WILLNEED:
	case MADV_DONTNEED:
	case MADV_FREE:
		if (start == end)
			return (0);
		modify_map = false;
		vm_map_lock_read(map);
		break;
	default:
		return (EINVAL);
	}

	/*
	 * Locate starting entry and clip if necessary.
	 */
	VM_MAP_RANGE_CHECK(map, start, end);

	if (modify_map) {
		/*
		 * madvise behaviors that are implemented in the vm_map_entry.
		 *
		 * We clip the vm_map_entry so that behavioral changes are
		 * limited to the specified address range.
		 */
		rv = vm_map_lookup_clip_start(map, start, &entry, &prev_entry);
		if (rv != KERN_SUCCESS) {
			vm_map_unlock(map);
			return (vm_mmap_to_errno(rv));