qemu: Enable slirp-helper iff dbus-vmstate present

The fact that qemu is capable -netdev socket is not enough to
start a migratable domain. It also needs dbus-vmstate capability.
Since there are already some qemu releases which have
net-socket-dgram capability and don't have dbus-vmstate we need
to check for dbus-vmstate.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

src/qemu/qemu_hotplug.c

@@ -1308,7 +1308,7 @@ qemuDomainAttachNetDevice(virQEMUDriverPtr driver,
 
     case VIR_DOMAIN_NET_TYPE_USER:
         if (!priv->disableSlirp &&
-            virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_NET_SOCKET_DGRAM)) {
+            virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_DBUS_VMSTATE)) {
             qemuSlirpPtr slirp = qemuInterfacePrepareSlirp(driver, net);
 
             if (!slirp)

src/qemu/qemu_process.c

@@ -5756,7 +5756,7 @@ qemuProcessNetworkPrepareDevices(virQEMUDriverPtr driver,
                 goto cleanup;
         } else if (actualType == VIR_DOMAIN_NET_TYPE_USER &&
                    !priv->disableSlirp &&
-                   virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_NET_SOCKET_DGRAM)) {
+                   virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_DBUS_VMSTATE)) {
             qemuSlirpPtr slirp = qemuInterfacePrepareSlirp(driver, net);
 
             QEMU_DOMAIN_NETWORK_PRIVATE(net)->slirp = slirp;

tests/qemuxml2argvdata/net-user.x86_64-4.0.0.args

@@ -29,7 +29,7 @@ file=/tmp/lib/domain--1-QEMUGuest1/master-key.aes \
 -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 \
 -drive file=/dev/HostVG/QEMUGuest1,format=raw,if=none,id=drive-ide0-0-0 \
 -device ide-hd,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0,bootindex=1 \
--netdev socket,fd=42,id=hostnet0 \
+-netdev user,id=hostnet0 \
 -device rtl8139,netdev=hostnet0,id=net0,mac=00:11:22:33:44:55,bus=pci.0,\
 addr=0x2 \
 -sandbox on,obsolete=deny,elevateprivileges=deny,spawn=deny,\

tests/qemuxml2argvtest.c

@@ -533,7 +533,7 @@ testCompareXMLToArgv(const void *data)
             virDomainNetDefPtr net = vm->def->nets[i];
 
             if (net->type == VIR_DOMAIN_NET_TYPE_USER &&
-                virQEMUCapsGet(info->qemuCaps, QEMU_CAPS_NET_SOCKET_DGRAM)) {
+                virQEMUCapsGet(info->qemuCaps, QEMU_CAPS_DBUS_VMSTATE)) {
                 qemuSlirpPtr slirp = qemuSlirpNew();
                 slirp->fd[0] = 42;
                 QEMU_DOMAIN_NETWORK_PRIVATE(net)->slirp = slirp;