Add v4l2loopback module

This eases using qubes-video-companion with dom0-provided kernel.

QubesOS/qubes-issues#6426

(cherry picked from commit 5ac5255)

.gitmodules

@@ -8,3 +8,6 @@
 	path = linux-utils
 	url = https://github.com/QubesOS/qubes-linux-utils.git
 	branch = release4.0
+[submodule "v4l2loopback"]
+	path = v4l2loopback
+	url = https://github.com/umlaeute/v4l2loopback

.qubesbuilder

@@ -7,6 +7,7 @@ source:
   - linux-utils
   - dummy-psu
   - dummy-backlight
+  - v4l2loopback
   files:
   - url: https://cdn.kernel.org/pub/linux/kernel/v5.x/linux-@[email protected]
     signature: https://cdn.kernel.org/pub/linux/kernel/v5.x/linux-@[email protected]

Makefile.builder

@@ -2,7 +2,7 @@ ifeq ($(PACKAGE_SET),dom0)
 RPM_SPEC_FILES := kernel.spec
 NO_ARCHIVE := 1
 
-INCLUDED_SOURCES = dummy-psu dummy-backlight linux-utils
+INCLUDED_SOURCES = dummy-psu dummy-backlight linux-utils v4l2loopback
 SOURCE_COPY_IN := $(INCLUDED_SOURCES)
 
 $(INCLUDED_SOURCES): SRC_SUBDIR=$@

kernel.spec.in

@@ -108,6 +108,7 @@ Source0:        linux-%{upstream_version}.tar
 Source1:        @dummy-psu@
 Source2:        @dummy-backlight@
 Source3:        @linux-utils@
+Source4:        @v4l2loopback@
 Source6:        macbook12-spi-driver-f85d028a41fbc928048c8ad248735501e76a2ce9.tar
 Source16:       guards
 Source17:       apply-patches
@@ -223,6 +224,9 @@ tar -x -C %_builddir -zf %{SOURCE2}
 rm -rf %_builddir/u2mfn
 tar -x -C %_builddir -zf %{SOURCE3} --strip-components=2 linux-utils/kernel-modules/u2mfn
 
+rm -rf %_builddir/v4l2loopback
+tar -x -C %_builddir -zf %{SOURCE4}
+
 rm -rf %_builddir/macbook12-spi-driver
 tar -x -C %_builddir -f %{SOURCE6}
 mv %_builddir/$(basename %{SOURCE6} .tar) %_builddir/macbook12-spi-driver
@@ -250,6 +254,11 @@ if [ -d "%_builddir/u2mfn" ]; then
     make -C %kernel_build_dir M=%_builddir/u2mfn modules
 fi
 
+# Build v4l2loopback module
+if [ -d "%_builddir/v4l2loopback" ]; then
+    make -C %kernel_build_dir M=%_builddir/v4l2loopback modules
+fi
+
 # Build applespi, apple-ibridge, apple-ib-tb, apple-ib-als modules
 if [ -d "%_builddir/macbook12-spi-driver" ]; then
     make -C %kernel_build_dir M=%_builddir/macbook12-spi-driver modules
@@ -317,6 +326,9 @@ fi
 if [ -d "%_builddir/u2mfn" ]; then
     make modules_install $MAKE_ARGS INSTALL_MOD_PATH=%buildroot M=%_builddir/u2mfn
 fi
+if [ -d "%_builddir/v4l2loopback" ]; then
+    make modules_install $MAKE_ARGS INSTALL_MOD_PATH=%buildroot M=%_builddir/v4l2loopback
+fi
 if [ -d "%_builddir/macbook12-spi-driver" ]; then
     make modules_install $MAKE_ARGS INSTALL_MOD_PATH=%buildroot M=%_builddir/macbook12-spi-driver
 fi