usb_util: add sandboxed-libusb feature

make open_fd patch optional. if sandboxed-libusb feature is not selected,
open_fd is not required.
In this case, the code must have access to /dev/bus/usb, and not
external fd is needed.

BUG=chromium:831850
TEST=cargo test

Change-Id: I21fa87dd15d08a03c2fe2b190559abbe6f63dcd5
Reviewed-on: https://chromium-review.googlesource.com/1375019
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Jingkui Wang <jkwang@google.com>
Reviewed-by: Zach Reizner <zachr@chromium.org>

3 files changed, 8 insertions, 4 deletions

diff --git a/Cargo.toml b/Cargo.toml
index 912f9c6..c8f7473 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -17,6 +17,7 @@ default-no-sandbox = []
 wl-dmabuf = ["devices/wl-dmabuf", "gpu_buffer", "resources/wl-dmabuf"]
 gpu = ["devices/gpu"]
 usb-emulation = ["usb_util"]
+sandboxed-libusb = ["usb_util/sandboxed-libusb"]
 
 [dependencies]
 arch = { path = "arch" }
diff --git a/usb_util/Cargo.toml b/usb_util/Cargo.toml
index bdb11f0..1ab1cf2 100644
--- a/usb_util/Cargo.toml
+++ b/usb_util/Cargo.toml
@@ -4,6 +4,9 @@ version = "0.1.0"
 authors = ["The Chromium OS Authors"]
 build = "build.rs"
 
+[features]
+sandboxed-libusb = []
+
 [dependencies]
 assertions = { path = "../assertions" }
 data_model = { path = "../data_model" }
diff --git a/usb_util/src/libusb_device.rs b/usb_util/src/libusb_device.rs
index 4ee80d2..d1a6e47 100644
--- a/usb_util/src/libusb_device.rs
+++ b/usb_util/src/libusb_device.rs
@@ -110,11 +110,11 @@ impl LibUsbDevice {
 
     /// Get device handle of this device. Take an external fd. This function is only safe when fd
     /// is an fd of this usb device.
+    #[cfg(feature = "sandboxed-libusb")]
     pub unsafe fn open_fd(&self, fd: RawFd) -> Result<DeviceHandle> {
         let mut handle: *mut bindings::libusb_device_handle = std::ptr::null_mut();
-        // Safe because 'self.device' is constructed from libusb device list and handle is on stack.
-        try_libusb!(unsafe { bindings::libusb_open_fd(self.device, fd, &mut handle) });
-        // Safe because handle is successfully initialized with libusb_open_fd.
-        Ok(unsafe { DeviceHandle::new(self._context.clone(), handle) })
+        // Safe when 'self.device' is constructed from libusb device list and handle is on stack.
+        try_libusb!(bindings::libusb_open_fd(self.device, fd, &mut handle));
+        Ok(DeviceHandle::new(self._context.clone(), handle))
     }
 }