inject snapshot-version in banner

if compiled from a git-clone

Related: v4l2loopback#469

Author: umlaeute

.gitversion

@@ -0,0 +1,3 @@
+this file is a dummy marker to notify the build-process
+that we are building from a development version of v4l2loopback.
+(that is: directly from a git-clone, rather than from a released tarball)

Makefile

@@ -1,3 +1,8 @@
+ifneq ($(wildcard .gitversion),)
+# building a snapshot version
+override KCPPFLAGS += -DSNAPSHOT_VERSION='"$(shell git describe --always --dirty 2>/dev/null || shell git describe --always 2>/dev/null || echo snapshot)"'
+endif
+
 include Kbuild
 ifeq ($(KBUILD_MODULES),)
 
@@ -43,7 +48,7 @@ all: v4l2loopback.ko utils
 v4l2loopback: v4l2loopback.ko
 v4l2loopback.ko:
 	@echo "Building v4l2-loopback driver..."
-	$(MAKE) -C $(KERNEL_DIR) M=$(PWD) modules
+	$(MAKE) -C $(KERNEL_DIR) M=$(PWD) KCPPFLAGS="$(KCPPFLAGS)" modules
 
 install-all: install install-utils install-man
 install:

v4l2loopback.c

@@ -2865,11 +2865,17 @@ static int __init v4l2loopback_init_module(void)
 
 	dprintk("module installed\n");
 
-	printk(KERN_INFO "v4l2loopback driver version %d.%d.%d loaded\n",
+	printk(KERN_INFO "v4l2loopback driver version %d.%d.%d%s loaded\n",
 	       // clang-format off
 	       (V4L2LOOPBACK_VERSION_CODE >> 16) & 0xff,
 	       (V4L2LOOPBACK_VERSION_CODE >>  8) & 0xff,
-	       (V4L2LOOPBACK_VERSION_CODE      ) & 0xff);
+	       (V4L2LOOPBACK_VERSION_CODE      ) & 0xff,
+#ifdef SNAPSHOT_VERSION
+	       " (" STRINGIFY2(SNAPSHOT_VERSION) ")"
+#else
+	       ""
+#endif
+	       );
 	// clang-format on
 
 	return 0;