displaytest.txt

\section{display test}

\begin{verbatim}
在此之前，i915驱动会加载display controller驱动。
display controller驱动会注册一个callback. i915的controller会在最后
尝试去调这个callback，把display的信息告诉display controller.
但是由于是在不同的线程里，当i915去调的时候可能还没注册好。所以，
在注册时，会检查一个变量ready_for_callback_，如果ready就补调一次。


main():
========
bind_display()
vfd = open("/dev/class/display-controller/000", O_RDWR);
  vopenat(AT_FDCWD, path, flags, ap);
    __fdio_open_at(&io, dirfd, path, flags, mode)
      fdio_iodir(&path, dirfd);
        iodir = fdio_root_handle;

      iodir->ops->open(iodir, clean, fdio_flags_to_zxio(flags), mode, io);
        调用的是mxdir_open
        ns_walk_locked(&vn, &path)
          vn_lookup_locked(vn, name, len);
          就找到/dev，是个remote
        zxrio_open_handle(vn->remote, path, flags, mode, out);
          把剩下的path传进去
          zxrio_getobject(h, ZXRIO_OPEN, path, flags, mode, &info, &control_channel);
            老一套，建通道，传一头，返回另一头
            zxrio_connect(rio_h, h1, ZXRIO_OPEN, flags, mode, name)

    fd = fdio_bind_to_fd(io, -1, 0)

devmgr收到ZXRIO_OPEN请求：

devfs_open(dn, h, path, flags);
  devfs_walk(&dn, path, &path);
    找到对应于"class/display-controller/000"的那个devnode_t
    发送ZXRIO_OPEN消息给devhost，对应于display_controller

devhost:
devhost_get_handles(h, dev, name, flags);
  device_open_at(dev, &dev, path, flags)
    devhost_device_open_at(dev, out, path, flags);
      dev_op_open_at(dev, out, path, flags);
        Controller::DdkOpenAt(zx_device_t** dev_out, const char* path, uint32_t flags)
          client = fbl::make_unique_checked<ClientProxy>(&ac, this, is_vc);
          client->Init();
            handler_.Init(&client_handle_);
              创建通道，一头挂在自己的api wait上，另一头给client_handle_

          client->OnDisplaysChanged(current_displays, idx, nullptr, 0)
            Client::OnDisplaysChanged
          client->DdkAdd(is_vc ? "dc-vc" : "dc", DEVICE_ADD_INSTANCE)

回到display-test main.cpp:
bind_display()
  ioctl_display_controller_get_handle(vfd, &dc_handle)

devhost:
ClientProxy::DdkIoctl
    out_buf = client_handle_.release();
    把之前创建的通道的一头返回。

  msg.Read(dc_handle, 0)
\end{verbatim}