[kernel] Let endpoints get interrupt notifications

- Add a tag field to all endpoint messages, which doubles as a
  notification field
- Add a endpoint_bind_irq syscall to enable an endpoint to listen for
  interrupt notifications. This mechanism needs to change.
- Add a temporary copy of the serial port code to nulldrv, and let it
  take responsibility for COM2

src/kernel/syscalls/endpoint.cpp

@@ -2,6 +2,7 @@
 #include "j6/types.h"
 
 #include "log.h"
+#include "device_manager.h"
 #include "objects/endpoint.h"
 #include "syscalls/helpers.h"
 
@@ -24,32 +25,55 @@ endpoint_close(j6_handle_t handle)
 }
 
 j6_status_t
-endpoint_send(j6_handle_t handle, size_t len, void *data)
+endpoint_send(j6_handle_t handle, j6_tag_t tag, size_t len, void *data)
 {
+	if (tag & j6_tag_system_flag)
+		return j6_err_invalid_arg;
+
 	endpoint *e = get_handle<endpoint>(handle);
 	if (!e) return j6_err_invalid_arg;
-	return e->send(len, data);
+
+	return e->send(tag, len, data);
 }
 
 j6_status_t
-endpoint_receive(j6_handle_t handle, size_t *len, void *data)
+endpoint_receive(j6_handle_t handle, j6_tag_t *tag, size_t *len, void *data)
 {
+	if (!tag || !len || (*len && !data))
+		return j6_err_invalid_arg;
+
 	endpoint *e = get_handle<endpoint>(handle);
 	if (!e) return j6_err_invalid_arg;
-	return e->receive(len, data);
+
+	return e->receive(tag, len, data);
 }
 
 j6_status_t
-endpoint_sendrecv(j6_handle_t handle, size_t *len, void *data)
+endpoint_sendrecv(j6_handle_t handle, j6_tag_t *tag, size_t *len, void *data)
 {
+	if (!tag || (*tag & j6_tag_system_flag))
+		return j6_err_invalid_arg;
+
 	endpoint *e = get_handle<endpoint>(handle);
 	if (!e) return j6_err_invalid_arg;
 
-	j6_status_t status = e->send(*len, data);
+	j6_status_t status = e->send(*tag, *len, data);
 	if (status != j6_status_ok)
 		return status;
 
-	return e->receive(len, data);
+	return e->receive(tag, len, data);
+}
+
+j6_status_t
+endpoint_bind_irq(j6_handle_t handle, unsigned irq)
+{
+	endpoint *e = get_handle<endpoint>(handle);
+	if (!e) return j6_err_invalid_arg;
+
+	if (device_manager::get().bind_irq(irq, e))
+		return j6_status_ok;
+
+	return j6_err_invalid_arg;
 }
 
 } // namespace syscalls