gpu: a few fixes for Windows build.

1. gpu_control_tube is not used on Windows yet. We will make use of
   it and test it in the downstream first before removing the Unix
   feature flag.
2. In Gpu::keep_rds(), skip appending descriptors of stdout and
   stderr since it is hard to find such descriptors on Windows, and
   this function won't be called on Windows anyways.
3. Some functions in gpu_display should be guarded with gfxstream
   feature flag, since we don't need to link against gfxstream
   binary when we are building/tesing without gfxstream.

BUG=b:213149288
TEST=presubmit

Change-Id: I28c3d16d82916e6d4a542aa008dd09015141716c
Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/3947825
Commit-Queue: Pujun Lun <lunpujun@google.com>
Reviewed-by: Daniel Verkamp <dverkamp@chromium.org>

devices/src/virtio/gpu/mod.rs

@@ -758,10 +758,13 @@ enum WorkerToken {
     CtrlQueue,
     CursorQueue,
     Display,
+    #[cfg(unix)]
     GpuControl,
     InterruptResample,
     Kill,
-    ResourceBridge { index: usize },
+    ResourceBridge {
+        index: usize,
+    },
     VirtioGpuPoll,
 }
 
@@ -810,6 +813,7 @@ impl<'a> EventManager<'a> {
 struct Worker {
     interrupt: Arc<Interrupt>,
     exit_evt_wrtube: SendTube,
+    #[cfg(unix)]
     gpu_control_tube: Tube,
     mem: GuestMemory,
     ctrl_queue: SharedQueueReader,
@@ -837,6 +841,7 @@ impl Worker {
             (&self.ctrl_evt, WorkerToken::CtrlQueue),
             (&self.cursor_evt, WorkerToken::CursorQueue),
             (&display_desc, WorkerToken::Display),
+            #[cfg(unix)]
             (&self.gpu_control_tube, WorkerToken::GpuControl),
             (&self.kill_evt, WorkerToken::Kill),
         ]) {
@@ -920,6 +925,7 @@ impl Worker {
                             let _ = self.exit_evt_wrtube.send::<VmEventType>(&VmEventType::Exit);
                         }
                     }
+                    #[cfg(unix)]
                     WorkerToken::GpuControl => {
                         let req = match self.gpu_control_tube.recv() {
                             Ok(req) => req,
@@ -1020,7 +1026,7 @@ impl DisplayBackend {
             DisplayBackend::X(display) => GpuDisplay::open_x(display.as_ref()),
             DisplayBackend::Stub => GpuDisplay::open_stub(),
             #[cfg(windows)]
-            DisplayBackend::WinAPI(display_properties) => match wndproc_thread.take() {
+            DisplayBackend::WinApi(display_properties) => match wndproc_thread.take() {
                 Some(wndproc_thread) => GpuDisplay::open_winapi(
                     wndproc_thread,
                     /* win_metrics= */ None,
@@ -1037,6 +1043,7 @@ impl DisplayBackend {
 
 pub struct Gpu {
     exit_evt_wrtube: SendTube,
+    #[cfg(unix)]
     gpu_control_tube: Option<Tube>,
     mapper: Option<Box<dyn SharedMemoryMapper>>,
     resource_bridges: Option<ResourceBridges>,
@@ -1064,7 +1071,7 @@ pub struct Gpu {
 impl Gpu {
     pub fn new(
         exit_evt_wrtube: SendTube,
-        gpu_control_tube: Tube,
+        #[cfg(unix)] gpu_control_tube: Tube,
         resource_bridges: Vec<Tube>,
         display_backends: Vec<DisplayBackend>,
         gpu_parameters: &GpuParameters,
@@ -1127,6 +1134,7 @@ impl Gpu {
 
         Gpu {
             exit_evt_wrtube,
+            #[cfg(unix)]
             gpu_control_tube: Some(gpu_control_tube),
             mapper: None,
             resource_bridges: Some(ResourceBridges::new(resource_bridges)),
@@ -1245,8 +1253,13 @@ impl Drop for Gpu {
 impl VirtioDevice for Gpu {
     fn keep_rds(&self) -> Vec<RawDescriptor> {
         let mut keep_rds = Vec::new();
+
+        // To find the RawDescriptor associated with stdout and stderr on Windows is difficult.
+        // Resource bridges are used only for Wayland displays. There is also no meaningful way
+        // casting the underlying DMA buffer wrapped in File to a copyable RawDescriptor.
         // TODO(davidriley): Remove once virgl has another path to include
         // debugging logs.
+        #[cfg(unix)]
         if cfg!(debug_assertions) {
             keep_rds.push(libc::STDOUT_FILENO);
             keep_rds.push(libc::STDERR_FILENO);
@@ -1265,6 +1278,7 @@ impl VirtioDevice for Gpu {
 
         keep_rds.push(self.exit_evt_wrtube.as_raw_descriptor());
 
+        #[cfg(unix)]
         if let Some(gpu_control_tube) = &self.gpu_control_tube {
             keep_rds.push(gpu_control_tube.as_raw_descriptor());
         }
@@ -1343,6 +1357,7 @@ impl VirtioDevice for Gpu {
             }
         };
 
+        #[cfg(unix)]
         let gpu_control_tube = match self.gpu_control_tube.take() {
             Some(gpu_control_tube) => gpu_control_tube,
             None => {
@@ -1421,6 +1436,7 @@ impl VirtioDevice for Gpu {
                         Worker {
                             interrupt: irq,
                             exit_evt_wrtube,
+                            #[cfg(unix)]
                             gpu_control_tube,
                             mem,
                             ctrl_queue: ctrl_queue.clone(),

gpu_display/src/gpu_display_win/window.rs

@@ -5,6 +5,7 @@
 use std::convert::From;
 use std::fmt;
 use std::mem;
+#[cfg(feature = "gfxstream")]
 use std::os::raw::c_int;
 use std::os::raw::c_void;
 use std::ptr::null_mut;
@@ -57,6 +58,7 @@ use winapi::um::winuser::*;
 use super::math_util::*;
 use super::HostWindowSpace;
 
+#[cfg(feature = "gfxstream")]
 #[link(name = "gfxstream_backend")]
 extern "C" {
     fn gfxstream_backend_setup_window(
@@ -212,6 +214,7 @@ impl Window {
     /// Updates the rectangle in the window's client area to which gfxstream renders.
     pub fn update_virtual_display_projection(&self, projection_box: &Box2D<i32, HostWindowSpace>) {
         // Safe because `Window` object won't outlive the HWND.
+        #[cfg(feature = "gfxstream")]
         unsafe {
             gfxstream_backend_setup_window(
                 self.hwnd as *const c_void,