Function vm_pager_get_pages

freebsd/vm/vm_pager.c:295–330

* Page in the pages for the object using its associated pager. * The requested page must be fully valid on successful return. */

 * The requested page must be fully valid on successful return.
 */
int
vm_pager_get_pages(vm_object_t object, vm_page_t *m, int count, int *rbehind,
    int *rahead)
{
#ifdef INVARIANTS
	vm_pindex_t pindex = m[0]->pindex;
#endif
	int r;

	vm_pager_assert_in(object, m, count);

	r = (*pagertab[object->type]->pgo_getpages)(object, m, count, rbehind,
	    rahead);
	if (r != VM_PAGER_OK)
		return (r);

	for (int i = 0; i < count; i++) {
		/*
		 * If pager has replaced a page, assert that it had
		 * updated the array.
		 */
#ifdef INVARIANTS
		VM_OBJECT_RLOCK(object);
		KASSERT(m[i] == vm_page_lookup(object, pindex++),
		    ("%s: mismatch page %p pindex %ju", __func__,
		    m[i], (uintmax_t )pindex - 1));
		VM_OBJECT_RUNLOCK(object);
#endif
		/*
		 * Zero out partially filled data.
		 */
		if (m[i]->valid != VM_PAGE_BITS_ALL)
			vm_page_zero_invalid(m[i], TRUE);
	}
	return (VM_PAGER_OK);
}

int
vm_pager_get_pages_async(vm_object_t object, vm_page_t *m, int count,