v4l2: Provide libcamerify wrapper script

Support easier usage of the v4l2 compatibility layer with a script that
handles the LD_PRELOAD for applications.

The wrapper can be prefixed to launch any application with the preload
set:

 $ libcamera-v4l2 v4l2-ctl --list-devices
 \_SB_.PCI0.GP13.XHC0.RHUB.PRT4- (libcamera:0):
 	/dev/video0

 platform/vimc.0 Sensor B (libcamera:1):
 	/dev/video2
 	/dev/video3
 	/dev/video4

Specifying '-d' once before the command to run will enable V4L2Compat
layer debug output from libcamera.

Specifying '-d' twice will enable all debug levels from all libcamera
components and provide a very detailed log for analysis.

Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>

src/v4l2/libcamerify.in

@@ -0,0 +1,47 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+help() {
+	echo "$0: Load an application with libcamera V4L2 compatibility layer preload"
+	echo " $0 [OPTIONS...] executable [args]"
+	echo " -d, --debug	Increase log level"
+}
+
+debug=0
+while [ $# -gt 0 ]; do
+	case $1 in
+		-d|--debug)
+			debug=$((debug+1))
+			;;
+		-h)
+			help;
+			exit 0
+			;;
+		--)
+			shift;
+			break;;
+		-*)
+			echo "Unrecognised option: $1";
+			help;
+			exit 1
+			;;
+		*)
+			break
+			;;
+	esac
+	shift
+done
+
+[ $debug -gt 0 ] && loglevel=V4L2Compat:0
+[ $debug -gt 1 ] && loglevel=0
+[ "$loglevel" != "" ] && export LIBCAMERA_LOG_LEVELS=$loglevel
+
+if [ "$LD_PRELOAD" = "" ] ; then
+   LD_PRELOAD='@LIBCAMERA_V4L2_SO@'
+else
+   LD_PRELOAD="$LD_PRELOAD "'@LIBCAMERA_V4L2_SO@'
+fi
+
+export LD_PRELOAD
+
+exec "$@"

src/v4l2/meson.build

@@ -33,3 +33,14 @@ v4l2_compat = shared_library('v4l2-compat',
                              install : true,
                              dependencies : [libcamera_private, libdl],
                              cpp_args : v4l2_compat_cpp_args)
+
+# Provide a wrapper script to support easily loading applications with the V4L2
+# adaptation layer.
+
+cdata = configuration_data()
+cdata.set('LIBCAMERA_V4L2_SO', get_option('prefix') / get_option('libdir') / 'v4l2-compat.so')
+
+configure_file(input : 'libcamerify.in',
+               output : 'libcamerify',
+               configuration : cdata,
+               install_dir : get_option('bindir'))