kernel: add a syscall to duplicate a handle

syscall/dispatch.c

@@ -23,6 +23,7 @@ static const virt_addr_t syscall_table[] = {
 	SYSCALL_TABLE_ENTRY(ADDRESS_SPACE_RELEASE, address_space_release),
 	SYSCALL_TABLE_ENTRY(KERN_LOG, kern_log),
 	SYSCALL_TABLE_ENTRY(KERN_HANDLE_CLOSE, kern_handle_close),
+	SYSCALL_TABLE_ENTRY(KERN_HANDLE_DUPLICATE, kern_handle_duplicate),
 	SYSCALL_TABLE_ENTRY(KERN_CONFIG_GET, kern_config_get),
 	SYSCALL_TABLE_ENTRY(KERN_CONFIG_SET, kern_config_set),
 	SYSCALL_TABLE_ENTRY(CHANNEL_CREATE, channel_create),

syscall/handle.c

@@ -4,5 +4,36 @@
 kern_status_t sys_kern_handle_close(kern_handle_t handle)
 {
 	struct task *self = current_task();
+
 	return task_close_handle(self, handle);
 }
+
+kern_status_t sys_kern_handle_duplicate(
+	kern_handle_t handle,
+	kern_handle_t *out)
+{
+	struct task *self = current_task();
+
+	if (!validate_access_w(self, out, sizeof *out)) {
+		return KERN_MEMORY_FAULT;
+	}
+
+	unsigned long flags;
+	task_lock_irqsave(self, &flags);
+
+	struct object *obj = NULL;
+	handle_flags_t handle_flags = 0;
+	kern_status_t status
+		= task_resolve_handle(self, handle, &obj, &handle_flags);
+	if (status != KERN_OK) {
+		task_unlock_irqrestore(self, flags);
+		return status;
+	}
+
+	status = task_open_handle(self, obj, handle_flags, out);
+	object_unref(obj);
+
+	task_unlock_irqrestore(self, flags);
+
+	return status;
+}