Function vnode_pager_alloc

freebsd/vm/vnode_pager.c:235–299

* Allocate (or lookup) pager for a vnode. * Handle is a vnode pointer. */

 * Handle is a vnode pointer.
 */
vm_object_t
vnode_pager_alloc(void *handle, vm_ooffset_t size, vm_prot_t prot,
    vm_ooffset_t offset, struct ucred *cred)
{
	vm_object_t object;
	struct vnode *vp;

	/*
	 * Pageout to vnode, no can do yet.
	 */
	if (handle == NULL)
		return (NULL);

	vp = (struct vnode *)handle;
	ASSERT_VOP_LOCKED(vp, "vnode_pager_alloc");
	VNPASS(vp->v_usecount > 0, vp);
retry:
	object = vp->v_object;

	if (object == NULL) {
		/*
		 * Add an object of the appropriate size
		 */
		object = vm_object_allocate(OBJT_VNODE,
		    OFF_TO_IDX(round_page(size)));

		object->un_pager.vnp.vnp_size = size;
		object->un_pager.vnp.writemappings = 0;
		object->domain.dr_policy = vnode_domainset;
		object->handle = handle;
		if ((vp->v_vflag & VV_VMSIZEVNLOCK) != 0) {
			VM_OBJECT_WLOCK(object);
			vm_object_set_flag(object, OBJ_SIZEVNLOCK);
			VM_OBJECT_WUNLOCK(object);
		}
		VI_LOCK(vp);
		if (vp->v_object != NULL) {
			/*
			 * Object has been created while we were allocating.
			 */
			VI_UNLOCK(vp);
			VM_OBJECT_WLOCK(object);
			KASSERT(object->ref_count == 1,
			    ("leaked ref %p %d", object, object->ref_count));
			object->type = OBJT_DEAD;
			refcount_init(&object->ref_count, 0);
			VM_OBJECT_WUNLOCK(object);
			vm_object_destroy(object);
			goto retry;
		}
		vp->v_object = object;
		VI_UNLOCK(vp);
		vrefact(vp);
	} else {
		vm_object_reference(object);
#if VM_NRESERVLEVEL > 0
		if ((object->flags & OBJ_COLORED) == 0) {
			VM_OBJECT_WLOCK(object);