A wrapper for starting a process conditionally on qvm-service

Add a generic wrapper that starts a given process only if specific
qvm-service is enabled. This can be used in desktop files for example
(in Exec= line). Note that systemd units have this functionality built
in (ConditionExists=).

QubesOS/qubes-issues#8161

debian/qubes-core-agent.install

@@ -145,6 +145,7 @@ usr/lib/qubes/qvm-copy-to-vm.gnome
 usr/lib/qubes/qvm-copy-to-vm.kde
 usr/lib/qubes/qvm-move-to-vm.gnome
 usr/lib/qubes/qvm-move-to-vm.kde
+usr/lib/qubes/qvm-service-wrapper
 usr/lib/qubes/resize-rootfs
 usr/lib/qubes/tar2qfile
 usr/lib/qubes/update-proxy-configs

misc/Makefile

@@ -1,6 +1,8 @@
 BINDIR ?= /usr/bin
 DATADIR ?= /usr/share
 SYSLIBDIR ?= /lib
+LIBDIR ?= /usr/lib
+QUBESLIBDIR := $(LIBDIR)/qubes
 UDEVRULESDIR := $(SYSLIBDIR)/udev/rules.d
 QUBESDATADIR := $(DATADIR)/qubes
 QUBESMIMEDIR := $(QUBESDATADIR)/xdg-override
@@ -39,6 +41,8 @@ install:
 	umask 022 && cp -r applications mime '$(DESTDIR)$(QUBESMIMEDIR)'
 	install -m 0755 -d $(DESTDIR)$(BINDIR)
 	install -m 0755 -t $(DESTDIR)$(BINDIR) qvm-features-request
+	install -m 0755 -d $(DESTDIR)$(QUBESLIBDIR)
+	install -m 0755 -t $(DESTDIR)$(QUBESLIBDIR) qvm-service-wrapper
 
 marker-vm: marker-vm.in
 	printf "$(VERSION)" | cut -f 1,2 -d . | cat $< - > marker-vm

misc/qvm-service-wrapper

@@ -0,0 +1,12 @@
+#!/bin/sh
+
+# Start an application given as $2 only if qvm-service $1 is enabled
+
+service="$1"
+shift
+if ! [ -r "/run/qubes-service/$service" ]; then
+    echo "Not starting '$1', qvm-service '$service' is not enabled" >&2
+    exit 0
+fi
+
+exec "$@"

rpm_spec/core-agent.spec.in

@@ -909,6 +909,7 @@ rm -f %{name}-%{version}
 /usr/lib/qubes/qvm-copy-to-vm.kde
 /usr/lib/qubes/qvm-move-to-vm.gnome
 /usr/lib/qubes/qvm-move-to-vm.kde
+/usr/lib/qubes/qvm-service-wrapper
 /usr/lib/qubes/tar2qfile
 /usr/lib/qubes/vm-file-editor
 /usr/lib/qubes/xdg-icon