1 files changed, 93 insertions, 0 deletions
diff --git a/devices/src/virtio/video/device.rs b/devices/src/virtio/video/device.rs
new file mode 100644
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+++ b/devices/src/virtio/video/device.rs
@@ -0,0 +1,93 @@
+// Copyright 2020 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+//! Definition of the trait `Device` that each backend video device must implement.
+
+#![allow(dead_code)] // TODO(keiichiw): Remove this attribute
+
+use sys_util::{PollContext, PollToken};
+
+use crate::virtio::resource_bridge::ResourceRequestSocket;
+use crate::virtio::video::command::{QueueType, VideoCmd};
+use crate::virtio::video::error::*;
+use crate::virtio::video::event::VideoEvt;
+use crate::virtio::video::response;
+
+#[derive(PollToken, Debug)]
+pub enum Token {
+    CmdQueue,
+    EventQueue,
+    EventFd { id: u32 },
+    Kill,
+    InterruptResample,
+}
+
+/// A tag for commands being processed asynchronously in the back-end device.
+/// TODO(b/149720783): Remove this enum by using async primitives.
+#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Copy, Debug)]
+pub enum AsyncCmdTag {
+    Queue {
+        stream_id: u32,
+        queue_type: QueueType,
+        resource_id: u32,
+    },
+    Drain {
+        stream_id: u32,
+    },
+    Clear {
+        stream_id: u32,
+        queue_type: QueueType,
+    },
+}
+
+/// A return value when a command from the guest is processed.
+#[derive(Debug)]
+pub enum VideoCmdResponseType {
+    /// The response for a synchronous command. This can be returned to the guest immediately via
+    /// command virtqueue.
+    Sync(response::CmdResponse),
+    /// The tag for an asynchronous command that the back-end device will complete.
+    /// Once the command is completed, its result will be sent with the same tag.
+    /// This can be seen as a poor man's future pattern.
+    Async(AsyncCmdTag),
+}
+
+/// A return value when processing a event the back-end device sent.
+#[derive(Debug)]
+pub enum VideoEvtResponseType {
+    /// The response for an asynchronous command that was enqueued through `process_cmd` before.
+    /// The `tag` must be same as the one returned when the command is enqueued.
+    AsyncCmd {
+        tag: AsyncCmdTag,
+        resp: VideoResult<response::CmdResponse>,
+    },
+    /// The event that happened in the back-end device.
+    Event(VideoEvt),
+}
+
+pub trait Device {
+    /// Processes a virtio-video command.
+    /// If the command expects a synchronous response, it returns a response as `VideoCmdResponseType::Sync`.
+    /// Otherwise, it returns a name of the descriptor chain that will be used when a response is prepared.
+    /// Implementations of this method is passed a PollContext object which can be used to add or remove
+    /// FDs to poll. It is expected that only Token::EventFd items would be added. When a Token::EventFd
+    /// event arrives, process_event_fd() will be invoked.
+    /// TODO(b/149720783): Make this an async function.
+    fn process_cmd(
+        &mut self,
+        cmd: VideoCmd,
+        poll_ctx: &PollContext<Token>,
+        resource_bridge: &ResourceRequestSocket,
+    ) -> VideoResult<VideoCmdResponseType>;
+
+    /// Processes an available Token::EventFd event.
+    /// If the message is sent via commandq, the return value is `VideoEvtResponseType::AsyncCmd`.
+    /// Otherwise (i.e. case of eventq), it's `VideoEvtResponseType::Event`.
+    /// TODO(b/149720783): Make this an async function.
+    fn process_event_fd(&mut self, stream_id: u32) -> Option<VideoEvtResponseType>;
+
+    /// Returns an ID for an available output resource that can be used to notify EOS.
+    /// Note that this resource must be enqueued by `ResourceQueue` and not be returned yet.
+    fn take_resource_id_to_notify_eos(&mut self, stream_id: u32) -> Option<u32>;
+}