Function vmem_clip

freebsd/kern/subr_vmem.c:995–1035

* vmem_clip: Trim the boundary tag edges to the requested start and size. */

 * vmem_clip:  Trim the boundary tag edges to the requested start and size.
 */
static void
vmem_clip(vmem_t *vm, bt_t *bt, vmem_addr_t start, vmem_size_t size)
{
	bt_t *btnew;
	bt_t *btprev;

	VMEM_ASSERT_LOCKED(vm);
	MPASS(bt->bt_type == BT_TYPE_FREE);
	MPASS(bt->bt_size >= size);
	bt_remfree(vm, bt);
	if (bt->bt_start != start) {
		btprev = bt_alloc(vm);
		btprev->bt_type = BT_TYPE_FREE;
		btprev->bt_start = bt->bt_start;
		btprev->bt_size = start - bt->bt_start;
		bt->bt_start = start;
		bt->bt_size -= btprev->bt_size;
		bt_insfree(vm, btprev);
		bt_insseg(vm, btprev,
		    TAILQ_PREV(bt, vmem_seglist, bt_seglist));
	}
	MPASS(bt->bt_start == start);
	if (bt->bt_size != size && bt->bt_size - size > vm->vm_quantum_mask) {
		/* split */
		btnew = bt_alloc(vm);
		btnew->bt_type = BT_TYPE_BUSY;
		btnew->bt_start = bt->bt_start;
		btnew->bt_size = size;
		bt->bt_start = bt->bt_start + size;
		bt->bt_size -= size;
		bt_insfree(vm, bt);
		bt_insseg(vm, btnew,
		    TAILQ_PREV(bt, vmem_seglist, bt_seglist));
		bt_insbusy(vm, btnew);
		bt = btnew;
	} else {
		bt->bt_type = BT_TYPE_BUSY;
		bt_insbusy(vm, bt);
	}
	MPASS(bt->bt_size >= size);
}

static int
vmem_try_fetch(vmem_t *vm, const vmem_size_t size, vmem_size_t align, int flags)