[kernel] Add VMA interface

Finished the VMA kobject and added the related syscalls. Processes can
now allocate memory! Other changes in this commit:

- stop using g_frame_allocator and add frame_allocator::get()
- make sure to release all handles in the process dtor
- fix kutil::map::iterator never comparing to end()

src/kernel/syscalls/vm_area.cpp

@@ -0,0 +1,61 @@
+#include "j6/errors.h"
+#include "j6/signals.h"
+#include "j6/types.h"
+
+#include "log.h"
+#include "objects/process.h"
+#include "objects/vm_area.h"
+#include "syscalls/helpers.h"
+#include "vm_space.h"
+
+namespace syscalls {
+
+j6_status_t
+vma_create(j6_handle_t *handle, size_t size)
+{
+	construct_handle<vm_area>(handle, size);
+	return j6_status_ok;
+}
+
+j6_status_t
+vma_create_map(j6_handle_t *handle, size_t size, uintptr_t base)
+{
+	vm_area *a = construct_handle<vm_area>(handle, size);
+	a->add_to(&process::current().space(), base);
+	return j6_status_ok;
+}
+
+j6_status_t
+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);
+	return j6_status_ok;
+}
+
+j6_status_t
+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());
+	return j6_status_ok;
+}
+
+j6_status_t
+vma_close(j6_handle_t handle)
+{
+	j6_status_t status = vma_unmap(handle);
+	if (status != j6_status_ok)
+		return status;
+
+	remove_handle<vm_area>(handle);
+	return j6_status_ok;
+}
+
+
+
+} // namespace syscalls