libvirtd: systemd: add special target for system shutdown

It is already discussed in "[RFC] daemon: remove hardcode dep on libvirt-guests" [1].

Mgmt can use means to save/restore domains on system shutdown/boot other than
libvirt-guests.service. Thus we need to specify appropriate ordering dependency between
libvirtd, domains and save/restore service. This patch takes approach suggested
in RFC and introduces a systemd target, so that ordering can be built next way:

libvirtd -> domain -> virt-guest-shutdown.target -> save-restore.service.

This way domains are decoupled from specific shutdown service via intermediate
target.

[1] https://www.redhat.com/archives/libvir-list/2016-September/msg01353.html

daemon/Makefile.am

@@ -67,6 +67,7 @@ EXTRA_DIST =						\
 	libvirt.rules					\
 	libvirtd.sasl					\
 	libvirtd.service.in				\
+	virt-guest-shutdown.target		\
 	libvirtd.sysconf				\
 	libvirtd.sysctl					\
 	libvirtd.aug                                    \
@@ -456,8 +457,11 @@ install-init-systemd: install-sysconfig libvirtd.service
 	$(MKDIR_P) $(DESTDIR)$(SYSTEMD_UNIT_DIR)
 	$(INSTALL_DATA) libvirtd.service \
 	  $(DESTDIR)$(SYSTEMD_UNIT_DIR)/libvirtd.service
+	$(INSTALL_DATA) virt-guest-shutdown.target \
+	  $(DESTDIR)$(SYSTEMD_UNIT_DIR)/virt-guest-shutdown.target
 
 uninstall-init-systemd: uninstall-sysconfig
+	rm -f $(DESTDIR)$(SYSTEMD_UNIT_DIR)/virt-guest-shutdown.target
 	rm -f $(DESTDIR)$(SYSTEMD_UNIT_DIR)/libvirtd.service
 	rmdir $(DESTDIR)$(SYSTEMD_UNIT_DIR) || :
 else ! LIBVIRT_INIT_SCRIPT_SYSTEMD

daemon/virt-guest-shutdown.target

+[Unit]
+Description=Libvirt guests shutdown
+Documentation=http://libvirt.org

libvirt.spec.in

@@ -1589,6 +1589,7 @@ exit 0
 
 %if %{with_systemd}
 %{_unitdir}/libvirtd.service
+%{_unitdir}/virt-guest-shutdown.target
 %{_unitdir}/virtlogd.service
 %{_unitdir}/virtlogd.socket
 %{_unitdir}/virtlockd.service

src/util/virsystemd.c

@@ -370,7 +370,7 @@ int virSystemdCreateMachine(const char *name,
                               3,
                               "Slice", "s", slicename,
                               "After", "as", 1, "libvirtd.service",
-                              "Before", "as", 1, "libvirt-guests.service") < 0)
+                              "Before", "as", 1, "virt-guest-shutdown.target") < 0)
             goto cleanup;
 
         if (error.level == VIR_ERR_ERROR) {
@@ -411,7 +411,7 @@ int virSystemdCreateMachine(const char *name,
                               3,
                               "Slice", "s", slicename,
                               "After", "as", 1, "libvirtd.service",
-                              "Before", "as", 1, "libvirt-guests.service") < 0)
+                              "Before", "as", 1, "virt-guest-shutdown.target") < 0)
             goto cleanup;
     }
 

tools/libvirt-guests.service.in

 [Unit]
 Description=Suspend/Resume Running libvirt Guests
 Wants=libvirtd.service
+Requires=virt-guest-shutdown.target
 After=network.target
 After=time-sync.target
 After=libvirtd.service
+After=virt-guest-shutdown.target
 Documentation=man:libvirtd(8)
 Documentation=http://libvirt.org