qemu_domain: Set 'passt' net backend if 'default' is unsupported

It may happen that QEMU is compiled without SLIRP but with
support for passt. In such case it is acceptable to alter user
provided configuration and switch backend to passt as it offers
all the features as SLIRP.

Resolves: https://issues.redhat.com/browse/RHEL-45518
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>

diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
index 1a90311ca5d609ed91cc380625e3cc91f326b060..2134b1103891778082b380e8319eb6d861060021 100644 (file)
--- a/src/qemu/qemu_domain.c
+++ b/src/qemu/qemu_domain.c
@@ -5975,12 +5975,25 @@ qemuDomainDeviceNetDefPostParse(virDomainNetDef *net,
                                 virQEMUCaps *qemuCaps)
 {
     if (net->type == VIR_DOMAIN_NET_TYPE_VDPA &&
-        !virDomainNetGetModelString(net))
+        !virDomainNetGetModelString(net)) {
         net->model = VIR_DOMAIN_NET_MODEL_VIRTIO;
-    else if (net->type != VIR_DOMAIN_NET_TYPE_HOSTDEV &&
+    } else if (net->type != VIR_DOMAIN_NET_TYPE_HOSTDEV &&
         !virDomainNetGetModelString(net) &&
-        virDomainNetResolveActualType(net) != VIR_DOMAIN_NET_TYPE_HOSTDEV)
+        virDomainNetResolveActualType(net) != VIR_DOMAIN_NET_TYPE_HOSTDEV) {
         net->model = qemuDomainDefaultNetModel(def, qemuCaps);
+    }
+
+    if (net->type == VIR_DOMAIN_NET_TYPE_USER &&
+        net->backend.type == VIR_DOMAIN_NET_BACKEND_DEFAULT) {
+        virDomainCapsDeviceNet netCaps = { };
+
+        virQEMUCapsFillDomainDeviceNetCaps(qemuCaps, &netCaps);
+
+        if (!VIR_DOMAIN_CAPS_ENUM_IS_SET(netCaps.backendType, VIR_DOMAIN_NET_BACKEND_DEFAULT) &&
+            VIR_DOMAIN_CAPS_ENUM_IS_SET(netCaps.backendType, VIR_DOMAIN_NET_BACKEND_PASST)) {
+            net->backend.type = VIR_DOMAIN_NET_BACKEND_PASST;
+        }
+    }
 
     return 0;
 }