Dynamically allocate video device

Makefile

@@ -36,7 +36,10 @@ install-vm: install-both
 	$(INSTALL_DIR) $(DESTDIR)$(BINDIR)
 	$(INSTALL_PROGRAM) receiver/$(PKGNAME) $(DESTDIR)$(BINDIR)
 	$(INSTALL_DIR) $(DESTDIR)$(DATADIR)/$(PKGNAME)/receiver
-	$(INSTALL_PROGRAM) receiver/setup.sh receiver/receiver.py receiver/destroy.sh receiver/common.sh $(DESTDIR)$(DATADIR)/$(PKGNAME)/receiver
+	$(INSTALL_PROGRAM) receiver/setup.py receiver/receiver.py receiver/destroy.py $(DESTDIR)$(DATADIR)/$(PKGNAME)/receiver
+	$(INSTALL_DATA) receiver/qubes-video-companion.rules $(DESTDIR)/usr/lib/udev/rules.d/80-qubes-video-companion.rules
+	$(INSTALL_DATA) receiver/qubes-video-companion.modprobe $(DESTDIR)/usr/lib/modprobe.d/qubes-video-companion.conf
+	$(INSTALL_DATA) receiver/qubes-video-companion.sudoers $(DESTDIR)/etc/sudoers.d/qubes-video-companion
 	$(INSTALL_DIR) $(DESTDIR)$(SYSCONFDIR)/qubes/rpc-config
 	echo 'wait-for-session=1' > $(DESTDIR)$(SYSCONFDIR)/qubes/rpc-config/qvc.Webcam
 	echo 'wait-for-session=1' > $(DESTDIR)$(SYSCONFDIR)/qubes/rpc-config/qvc.ScreenShare

receiver/destroy.py

@@ -0,0 +1,51 @@
+#!/usr/bin/python3 --
+#
+# Copyright (C) 2025 Marek Marczykowski-Górecki
+#                            <marmarek@invisiblethingslab.com>
+# Licensed under the MIT License. See LICENSE file for details.
+
+import errno
+import sys
+import os
+import fcntl
+import time
+import subprocess
+
+
+# V4L2LOOPBACK_CTL_REMOVE = 0x40487e02
+# use legacy numbers since the change was recent
+V4L2LOOPBACK_CTL_REMOVE = 0x4C81
+
+
+def unregister_device(dev_nr):
+    ctrl_fd = os.open("/dev/v4l2loopback", os.O_RDWR)
+    try:
+        message = ("Please close any window that has an open video stream "
+            "so kernel modules can be securely unloaded...")
+
+        while True:
+            try:
+                fcntl.ioctl(ctrl_fd, V4L2LOOPBACK_CTL_REMOVE, dev_nr)
+                break
+            except OSError as e:
+                if e.errno == errno.EBUSY:
+                    print(message, file=sys.stderr)
+                    subprocess.call(
+                        ["notify-send", "Qubes Video Companion", message]
+                    )
+                    time.sleep(10)
+                else:
+                    raise
+    finally:
+        os.close(ctrl_fd)
+
+
+def main(argv):
+    if len(argv) != 2 or not argv[1].startswith("/dev/video"):
+        raise RuntimeError("Wrong arguments, expected /dev/video* path")
+    dev_nr = int(argv[1][len("/dev/video") :])
+    unregister_device(dev_nr)
+
+
+if __name__ == "__main__":
+    main(sys.argv)

receiver/qubes-video-companion

@@ -56,8 +56,7 @@ esac
 exit_clean () {
     exit_code="$?"
 
-    /usr/share/qubes-video-companion/receiver/destroy.sh
-    sudo rm -f "$qvc_lock_file"
+    /usr/share/qubes-video-companion/receiver/destroy.py "$dev_path"
 
     if [ "$video_source" = "webcam" ] && [ "$exit_code" = "141" ]; then
         echo "The webcam device is in use! Please stop any instance of Qubes Video Companion running on another qube." >&2
@@ -67,15 +66,7 @@ exit_clean () {
     exit "$exit_code"
 }
 
-qvc_lock_file="/run/lock/qubes-video-companion"
-if ! [ -f "$qvc_lock_file" ]; then
-    trap exit_clean EXIT
-    sudo touch "$qvc_lock_file"
-else
-    echo "Qubes Video Companion is already running! Please stop the previous session before starting a new one. If you think this is an error, remove the lockfile $qvc_lock_file" >&2
-    exit 1
-fi
-
-/usr/share/qubes-video-companion/receiver/setup.sh
+dev_path=$(/usr/share/qubes-video-companion/receiver/setup.py "$video_source")
+trap exit_clean EXIT
 # Filter standard error escape characters for safe printing to the terminal from the video sender
-qrexec-client-vm --filter-escape-chars-stderr -- "$qube" "$qvc_service+$resolution" /usr/share/qubes-video-companion/receiver/receiver.py
+qrexec-client-vm --filter-escape-chars-stderr -- "$qube" "$qvc_service+$resolution" /usr/share/qubes-video-companion/receiver/receiver.py "$dev_path"

receiver/qubes-video-companion.modprobe

@@ -0,0 +1 @@
+options v4l2loopback devices=0

receiver/qubes-video-companion.rules

@@ -0,0 +1 @@
+KERNEL=="v4l2loopback", GROUP="qubes", MODE="0660"

receiver/qubes-video-companion.sudoers

@@ -0,0 +1 @@
+%qubes ALL = (root) NOPASSWD: /usr/sbin/modprobe v4l2loopback

receiver/receiver.py

@@ -11,8 +11,13 @@
 
 
 def main(argv) -> NoReturn:
-    if len(argv) != 1:
-        raise RuntimeError("should not have any arguments")
+    dev_path = "/dev/video0"
+    if len(argv) == 2:
+        dev_path = argv[1]
+    elif len(argv) != 1:
+        raise RuntimeError(
+            "wrong arguments - expected only optional device path"
+        )
 
     width, height, fps = read_video_parameters()
 
@@ -45,7 +50,7 @@ def main(argv) -> NoReturn:
             "use-sink-caps=true",
             "!",
             "v4l2sink",
-            "device=/dev/video0",
+            "device=" + dev_path,
             "sync=false",
         ),
     )

receiver/setup.py

@@ -0,0 +1,113 @@
+#!/usr/bin/python3 --
+#
+# Copyright (C) 2025 Marek Marczykowski-Górecki
+#                            <marmarek@invisiblethingslab.com>
+# Licensed under the MIT License. See LICENSE file for details.
+
+
+import sys
+import struct
+import os
+import fcntl
+import subprocess
+
+# see v4l2loopback.h:
+#    __s32 output_nr;
+#    __s32 unused; /*capture_nr;*/
+#
+#    /**
+#         * a nice name for your device
+#         * if (*card_label)==0, an automatic name is assigned
+#         */
+#    char card_label[32];
+#
+#    /**
+#         * allowed frame size
+#         * if too low, default values are used
+#         */
+#    __u32 min_width;
+#    __u32 max_width;
+#    __u32 min_height;
+#    __u32 max_height;
+#
+#    /**
+#         * number of buffers to allocate for the queue
+#         * if set to <=0, default values are used
+#         */
+#    __s32 max_buffers;
+#
+#    /**
+#         * how many consumers are allowed to open this device concurrently
+#         * if set to <=0, default values are used
+#         */
+#    __s32 max_openers;
+#
+#    /**
+#         * set the debugging level for this device
+#         */
+#    __s32 debug;
+#
+#    /**
+#         * whether to announce OUTPUT/CAPTURE capabilities exclusively
+#         * for this device or not
+#         * (!exclusive_caps)
+#     * NOTE: this is going to be removed once separate output/capture
+#     *       devices are implemented
+#         */
+#    __s32 announce_all_caps;
+v4l2_loopback_config_format = "ii32sIIIIiiii"
+
+
+# V4L2LOOPBACK_CTL_ADD = 0x40487e01
+# use legacy numbers since the change was recent
+V4L2LOOPBACK_CTL_ADD = 0x4C80
+
+
+def register_device(name):
+    ctrl_fd = os.open("/dev/v4l2loopback", os.O_RDWR)
+    try:
+        if not name:
+            name = "Qubes Video Companion"
+        # arg is v4l2_loopback_config config struct
+        conf = bytearray(
+            struct.pack(
+                v4l2_loopback_config_format,
+                -1,  # output_nr (auto)
+                -1,  # unused
+                name.encode(),  # card_label
+                0,  # min_width
+                0,  # max_width
+                0,  # min_height
+                0,  # max_height
+                0,  # max_buffers
+                0,  # max_openers
+                0,  # debug
+                0,  # announce_all_caps
+            )
+        )
+        ret = fcntl.ioctl(ctrl_fd, V4L2LOOPBACK_CTL_ADD, conf)
+        return ret
+    finally:
+        os.close(ctrl_fd)
+
+
+def main(argv):
+    name = None
+    if len(argv) == 2:
+        name = f"QVC - {argv[1]}"
+    elif len(argv) != 1:
+        raise RuntimeError("Invalid arguments - usage: setup.py [name]")
+    if not os.path.exists("/dev/v4l2loopback"):
+        subprocess.check_call(
+            ["sudo", "--non-interactive", "modprobe", "v4l2loopback"]
+        )
+        # wait for udev to apply permission
+        subprocess.check_call(
+            ["udevadm", "wait", "--settle", "/dev/v4l2loopback"]
+        )
+    dev_nr = register_device(name)
+    print(f"/dev/video{dev_nr}")
+
+
+if __name__ == "__main__":
+    main(sys.argv)

rpm_spec/qubes-video-companion.spec.in

@@ -103,12 +103,14 @@ This package contains the video-receiving portion of Qubes Video Companion.
 %{_sysconfdir}/dkms/v4l2loopback.conf
 %{_mandir}/man1/qubes-video-companion.1.gz
 %{_bindir}/qubes-video-companion
-%{_datadir}/qubes-video-companion/receiver/setup.sh
+%{_datadir}/qubes-video-companion/receiver/setup.py
 %{_datadir}/qubes-video-companion/receiver/receiver.py
-%{_datadir}/qubes-video-companion/receiver/destroy.sh
-%{_datadir}/qubes-video-companion/receiver/common.sh
+%{_datadir}/qubes-video-companion/receiver/destroy.py
 /usr/share/applications/qubes-video-companion-webcam.desktop
 /usr/share/applications/qubes-video-companion-screenshare.desktop
+/usr/lib/udev/rules.d/80-qubes-video-companion.rules
+/usr/lib/modprobe.d/qubes-video-companion.conf
+/etc/sudoers.d/qubes-video-companion
 
 %package docs
 Summary:        Documentation for qubes-video-companion

tests/qvctests/integ.py

@@ -91,6 +91,11 @@ def test_010_screenshare(self):
         source_image = self.capture_from_screen(self.source)
         destination_image = self.capture_from_video(self.view)
         diff = self.compare_images(source_image, destination_image)
+        if diff >= 2.0:
+            with open(f"/tmp/window-dump-{self.id()}-source", "wb") as f:
+                f.write(source_image)
+            with open(f"/tmp/window-dump-{self.id()}-dest", "wb") as f:
+                f.write(destination_image)
         self.assertLess(diff, 2.0)
         self.click_stop(self.source, 'screenshare')
         # wait for device to disappear, or a timeout
@@ -171,6 +176,11 @@ def test_020_webcam(self):
         source_image = self.capture_from_video(self.source, ",width=640,height=480")
         source_image = self.apply_mask(source_image)
         diff = self.compare_images(source_image, destination_image)
+        if diff >= 2.5:
+            with open(f"/tmp/window-dump-{self.id()}-source", "wb") as f:
+                f.write(source_image)
+            with open(f"/tmp/window-dump-{self.id()}-dest", "wb") as f:
+                f.write(destination_image)
         self.assertLess(diff, 2.5)