[zion] Create a message queue to be shared between the port and channel

zion/lib/message_queue.h

@@ -0,0 +1,44 @@
+#pragma once
+
+#include "capability/capability.h"
+#include "include/ztypes.h"
+#include "lib/linked_list.h"
+#include "lib/shared_ptr.h"
+
+class MessageQueue {
+ public:
+  virtual ~MessageQueue() {}
+
+  virtual z_err_t PushBack(uint64_t num_bytes, const void* bytes,
+                           uint64_t num_caps, const z_cap_t* caps) = 0;
+  virtual z_err_t PopFront(uint64_t* num_bytes, void* bytes, uint64_t* num_caps,
+                           z_cap_t* caps) = 0;
+};
+
+class UnboundedMessageQueue : public MessageQueue {
+ public:
+  UnboundedMessageQueue() {}
+  UnboundedMessageQueue(const UnboundedMessageQueue&) = delete;
+  UnboundedMessageQueue& operator=(const UnboundedMessageQueue&) = delete;
+  virtual ~UnboundedMessageQueue() override {}
+
+  z_err_t PushBack(uint64_t num_bytes, const void* bytes, uint64_t num_caps,
+                   const z_cap_t* caps) override;
+  z_err_t PopFront(uint64_t* num_bytes, void* bytes, uint64_t* num_caps,
+                   z_cap_t* caps) override;
+
+  void WriteKernel(uint64_t init, RefPtr<Capability> cap);
+
+  uint64_t size() { return pending_messages_.size(); }
+  bool empty() { return size() == 0; }
+
+ private:
+  struct Message {
+    uint64_t num_bytes;
+    uint8_t* bytes;
+
+    LinkedList<RefPtr<Capability>> caps;
+  };
+
+  LinkedList<SharedPtr<Message>> pending_messages_;
+};