[kernel] Spit out vm_area types

The vm_space allow() functionality was a bit janky; using VMAs for all
regions would be a lot cleaner. To that end, this change:

- Adds a "static array" ctor to kutil::vector for setting the kernel
  address space's VMA list. This way a kernel heap VMA can be created
  without the heap already existing.
- Splits vm_area into different subclasses depending on desired behavior
- Splits out the concept of vm_mapper which maps vm_areas to vm_spaces,
  so that some kinds of VMA can be inherently single-space
- Implements VMA resizing so that userspace can grow allocations.
- Obsolete page_table_indices is removed

Also, the following bugs were fixed:

- kutil::map iterators on empty maps no longer break
- memory::page_count was doing page-align, not page-count

See: Github bug #242
See: [frobozz blog post](https://jsix.dev/posts/frobozz/)

Tags:

src/kernel/syscalls/vm_area.cpp

@@ -11,17 +11,19 @@
 namespace syscalls {
 
 j6_status_t
-vma_create(j6_handle_t *handle, size_t size)
+vma_create(j6_handle_t *handle, size_t size, uint32_t flags)
 {
-	construct_handle<vm_area>(handle, size);
+	vm_flags f = vm_flags::user_mask & flags;
+	construct_handle<vm_area_shared>(handle, size, f);
 	return j6_status_ok;
 }
 
 j6_status_t
-vma_create_map(j6_handle_t *handle, size_t size, uintptr_t base)
+vma_create_map(j6_handle_t *handle, size_t size, uintptr_t base, uint32_t flags)
 {
-	vm_area *a = construct_handle<vm_area>(handle, size);
-	a->add_to(&process::current().space(), base);
+	vm_flags f = vm_flags::user_mask & flags;
+	vm_area *a = construct_handle<vm_area_shared>(handle, size, f);
+	process::current().space().add(base, a);
 	return j6_status_ok;
 }
 
@@ -31,7 +33,7 @@ vma_map(j6_handle_t handle, uintptr_t base)
 	vm_area *a = get_handle<vm_area>(handle);
 	if (!a) return j6_err_invalid_arg;
 
-	a->add_to(&process::current().space(), base);
+	process::current().space().add(base, a);
 	return j6_status_ok;
 }
 
@@ -41,7 +43,7 @@ vma_unmap(j6_handle_t handle)
 	vm_area *a = get_handle<vm_area>(handle);
 	if (!a) return j6_err_invalid_arg;
 
-	a->remove_from(&process::current().space());
+	process::current().space().remove(a);
 	return j6_status_ok;
 }
 
@@ -56,6 +58,19 @@ vma_close(j6_handle_t handle)
 	return j6_status_ok;
 }
 
+j6_status_t
+vma_resize(j6_handle_t handle, size_t *size)
+{
+	if (!size)
+		return j6_err_invalid_arg;
+
+	vm_area *a = get_handle<vm_area>(handle);
+	if (!a) return j6_err_invalid_arg;
+
+	*size = a->resize(*size);
+	return j6_status_ok;
+}
+
 
 
 } // namespace syscalls