From 11fb0a4cb7b71c93667b970c4019ecc3d324b3f5 Mon Sep 17 00:00:00 2001
From: Peter Johnson <johnson.peter@gmail.com>
Date: Sat, 13 Jun 2020 20:51:46 -0700
Subject: [PATCH] [cscore] EnumerateUsbCameras(): Only list capture devices
 (#2532)

Previously this would list ALL /dev/video* devices.  In recent versions of
Linux this leads to listing duplicate devices, as many USB cameras provide
both a video device and a metadata device, and only the video device can
actually be used for streaming.
---
 .../src/main/native/linux/UsbCameraImpl.cpp   | 21 +++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/cscore/src/main/native/linux/UsbCameraImpl.cpp b/cscore/src/main/native/linux/UsbCameraImpl.cpp
index 83bff75c68..453a37243c 100644
--- a/cscore/src/main/native/linux/UsbCameraImpl.cpp
+++ b/cscore/src/main/native/linux/UsbCameraImpl.cpp
@@ -223,6 +223,25 @@ static bool GetDescriptionIoctl(const char* cpath, std::string* desc) {
   return true;
 }
 
+static bool IsVideoCaptureDevice(const char* cpath) {
+  int fd = open(cpath, O_RDWR);
+  if (fd < 0) return false;
+
+  struct v4l2_capability vcap;
+  std::memset(&vcap, 0, sizeof(vcap));
+  if (DoIoctl(fd, VIDIOC_QUERYCAP, &vcap) < 0) {
+    close(fd);
+    return false;
+  }
+  close(fd);
+
+  return (vcap.capabilities & V4L2_CAP_VIDEO_CAPTURE) != 0 &&
+         (vcap.capabilities & V4L2_CAP_STREAMING) != 0 &&
+         ((vcap.capabilities & V4L2_CAP_DEVICE_CAPS) == 0 ||
+          ((vcap.device_caps & V4L2_CAP_VIDEO_CAPTURE) != 0 &&
+           (vcap.device_caps & V4L2_CAP_STREAMING) != 0));
+}
+
 static int GetDeviceNum(const char* cpath) {
   wpi::StringRef path{cpath};
   std::string pathBuf;
@@ -1453,6 +1472,8 @@ std::vector<UsbCameraInfo> EnumerateUsbCameras(CS_Status* status) {
       path += fname;
       info.path = path.str();
 
+      if (!IsVideoCaptureDevice(path.c_str())) continue;
+
       info.name = GetDescriptionImpl(path.c_str());
       if (info.name.empty()) continue;