guest: Add memory balloon by default

libvirt already does this for pretty much all QEMU guests, but
ARM virt guests for example don't get a memory balloon by default
at that level of the stack.

virt-manager is in a good position to make sure defaults are
consistent across architectures, and there's no downside in having
the device in the XML passed to libvirt anyway.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>

tests/cli-test-xml/compare/virt-install-aarch64-graphics.xml

@@ -40,6 +40,7 @@
     <video>
       <model type="virtio"/>
     </video>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-aarch64-headless.xml

@@ -34,6 +34,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-aarch64-kvm-gic.xml

@@ -41,6 +41,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-aarch64-kvm-import.xml

@@ -34,6 +34,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-arm-defaultmach-f20.xml

@@ -34,6 +34,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-arm-kvm-import.xml

@@ -34,6 +34,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-arm-virt-f20.xml

@@ -34,6 +34,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-f21-kvm-remote.xml

@@ -57,6 +57,7 @@
     </video>
     <redirdev bus="usb" type="spicevmc"/>
     <redirdev bus="usb" type="spicevmc"/>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-kvm-centos7.xml

@@ -61,6 +61,7 @@
     </video>
     <redirdev bus="usb" type="spicevmc"/>
     <redirdev bus="usb" type="spicevmc"/>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
@@ -127,6 +128,7 @@
     </video>
     <redirdev bus="usb" type="spicevmc"/>
     <redirdev bus="usb" type="spicevmc"/>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-kvm-fedoralatest-url.xml

@@ -51,6 +51,7 @@
     <video>
       <model type="qxl"/>
     </video>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
@@ -107,6 +108,7 @@
     <video>
       <model type="qxl"/>
     </video>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-kvm-session-defaults.xml

@@ -66,6 +66,7 @@
     </video>
     <redirdev bus="usb" type="spicevmc"/>
     <redirdev bus="usb" type="spicevmc"/>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
@@ -135,6 +136,7 @@
     </video>
     <redirdev bus="usb" type="spicevmc"/>
     <redirdev bus="usb" type="spicevmc"/>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-location-iso.xml

@@ -71,6 +71,7 @@
     </video>
     <redirdev bus="usb" type="spicevmc"/>
     <redirdev bus="usb" type="spicevmc"/>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
@@ -145,6 +146,7 @@
     </video>
     <redirdev bus="usb" type="spicevmc"/>
     <redirdev bus="usb" type="spicevmc"/>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-many-devices.xml

@@ -515,6 +515,7 @@
       <source path="/tmp/foo.socket"/>
       <log file="/tmp/123.log"/>
     </redirdev>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-network-install-resources.xml

@@ -43,6 +43,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
@@ -90,6 +91,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-osinfo-netinst-unattended.xml

@@ -49,6 +49,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
@@ -100,6 +101,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-osinfo-url-unattended.xml

@@ -43,6 +43,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
@@ -90,6 +91,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-osinfo-url-with-disk.xml

@@ -53,6 +53,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
@@ -110,6 +111,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-osinfo-url.xml

@@ -43,6 +43,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>
@@ -90,6 +91,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-ppc64-graphics.xml

@@ -38,6 +38,7 @@
     <video>
       <model type="vga"/>
     </video>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-ppc64-headless.xml

@@ -32,6 +32,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-ppc64-machdefault-f20.xml

@@ -39,6 +39,7 @@
     <video>
       <model type="vga"/>
     </video>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-ppc64-pseries-f20.xml

@@ -44,6 +44,7 @@
     <video>
       <model type="vga"/>
     </video>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-ppc64le-kvm-import.xml

@@ -38,6 +38,7 @@
     <video>
       <model type="vga"/>
     </video>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-qemu-32-on-64.xml

@@ -40,6 +40,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-riscv64-graphics.xml

@@ -38,6 +38,7 @@
     <video>
       <model type="virtio"/>
     </video>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-riscv64-headless.xml

@@ -32,6 +32,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-s390x-cdrom-KVMIBM.xml

@@ -46,6 +46,7 @@
       <model type="virtio"/>
     </video>
     <watchdog model="diag288" action="reset"/>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-s390x-cdrom.xml

@@ -41,6 +41,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-s390x-graphics.xml

@@ -39,6 +39,7 @@
     <video>
       <model type="virtio"/>
     </video>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-s390x-headless.xml

@@ -33,6 +33,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-x86_64-graphics.xml

@@ -50,6 +50,7 @@
     <video>
       <model type="qxl"/>
     </video>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

tests/cli-test-xml/compare/virt-install-x86_64-headless.xml

@@ -45,6 +45,7 @@
       <source mode="bind"/>
       <target type="virtio" name="org.qemu.guest_agent.0"/>
     </channel>
+    <memballoon model="virtio"/>
     <rng model="virtio">
       <backend model="random">/dev/urandom</backend>
     </rng>

virtinst/guest.py

@@ -735,6 +735,7 @@ class Guest(XMLBuilder):
         self._add_default_usb_controller()
         self._add_default_channels()
         self._add_default_rng()
+        self._add_default_memballoon()
 
         self.clock.set_defaults(self)
         self.cpu.set_defaults(self)
@@ -946,6 +947,37 @@ class Guest(XMLBuilder):
             dev.device = "/dev/urandom"
             self.add_device(dev)
 
+    def _add_default_memballoon(self):
+        if self.devices.memballoon:
+            return
+        if not self.conn.is_qemu():
+            return
+
+        # For most QEMU guests, libvirt will automatically add a memballoon
+        # device, which means that if the user has explicitly asked for it
+        # *not* to be present then we still need to create the device and
+        # set the model to "none" to let libvirt know
+        if self.disable_default_memballoon:
+            dev = DeviceMemballoon(self.conn)
+            dev.model = "none"
+            self.add_device(dev)
+            return
+
+        # We know for certain that a memballoon is good to have with these
+        # machine types; for other machine types, we leave the decision up
+        # to libvirt
+        if not (self.os.is_x86() or
+                self.os.is_arm_machvirt() or
+                self.os.is_riscv_virt() or
+                self.os.is_s390x() or
+                self.os.is_pseries()):
+            return
+
+        if self.osinfo.supports_virtioballoon():
+            dev = DeviceMemballoon(self.conn)
+            dev.model = "virtio"
+            self.add_device(dev)
+
     def _add_implied_controllers(self):
         has_any_scsi = False
         for dev in self.devices.controller: