Add a service to enable swap early - before fsck of the root filesystem

fsck may require significant amount of RAM, enable swap earlier to avoid
out of memory condition. Implement this as a separate service unit, not
a swap unit, because the latter requires udev running (implicit
dependency on dev-xvdc1.device) which is not the case before remounting
root filesystem read-write.

QubesOS/qubes-issues#6174

Makefile

@@ -101,7 +101,7 @@ install-init:
 	install -m 0644 init/functions $(DESTDIR)$(LIBDIR)/qubes/init/
 
 # Systemd service files
-SYSTEMD_ALL_SERVICES := $(wildcard vm-systemd/qubes-*.service)
+SYSTEMD_ALL_SERVICES := $(wildcard vm-systemd/qubes-*.service) vm-systemd/dev-xvdc1-swap.service
 SYSTEMD_NETWORK_SERVICES := vm-systemd/qubes-firewall.service vm-systemd/qubes-iptables.service vm-systemd/qubes-updates-proxy.service
 SYSTEMD_CORE_SERVICES := $(filter-out $(SYSTEMD_NETWORK_SERVICES), $(SYSTEMD_ALL_SERVICES))
 

debian/qubes-core-agent.install

@@ -83,6 +83,7 @@ lib/systemd/system/netfilter-persistent.service.d/30_qubes.conf
 lib/systemd/system/org.cups.cupsd.path.d/30_qubes.conf
 lib/systemd/system/org.cups.cupsd.service.d/30_qubes.conf
 lib/systemd/system/org.cups.cupsd.socket.d/30_qubes.conf
+lib/systemd/system/dev-xvdc1-swap.service
 lib/systemd/system/qubes-early-vm-config.service
 lib/systemd/system/qubes-misc-post.service
 lib/systemd/system/qubes-mount-dirs.service

rpm_spec/core-agent.spec.in

@@ -908,6 +908,7 @@ The Qubes core startup configuration for SystemD init.
 %files systemd
 %defattr(-,root,root,-)
 /etc/systemd/system/xendriverdomain.service
+/lib/systemd/system/dev-xvdc1-swap.service
 /lib/systemd/system/qubes-misc-post.service
 /lib/systemd/system/qubes-mount-dirs.service
 /lib/systemd/system/qubes-rootfs-resize.service

vm-systemd/75-qubes-vm.preset

@@ -107,6 +107,7 @@ enable qubes-sync-time.timer
 enable module-load-dummy-psu.service
 enable module-load-dummy-backlight.service
 enable qubes-psu-client@.service default sys-usb
+enable dev-xvdc1-swap.service
 
 # Disable useless Xen services in Qubes VM
 disable xenstored.service

vm-systemd/dev-xvdc1-swap.service

@@ -0,0 +1,13 @@
+[Unit]
+# have it as  .service, not .swap, because .swap has implicit dependency on
+# .device which needs udev running already
+Description=Enable swap on /dev/xvdc1 early
+DefaultDependencies=no
+Before=systemd-fsck-root.service
+
+[Service]
+Type=oneshot
+ExecStart=-/usr/sbin/swapon /dev/xvdc1
+
+[Install]
+WantedBy=sysinit.target

vm-systemd/systemd-fsck-root.service.d/30_qubes.conf

@@ -0,0 +1,2 @@
+[Unit]
+After=swap.target