qemu: alias: Fix calculation of RNG device aliases

For device hotplug, the new alias ID needs to be checked in the list
rather than using the count of devices. Unplugging a device that is not
last in the array will make further hotplug impossible due to alias
collision.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1324551

src/qemu/qemu_alias.c

@@ -382,10 +382,19 @@ qemuAssignDeviceRedirdevAlias(virDomainDefPtr def,
 
 
 int
-qemuAssignDeviceRNGAlias(virDomainRNGDefPtr rng,
-                         size_t idx)
+qemuAssignDeviceRNGAlias(virDomainDefPtr def,
+                         virDomainRNGDefPtr rng)
 {
-    if (virAsprintf(&rng->info.alias, "rng%zu", idx) < 0)
+    size_t i;
+    int maxidx = 0;
+    int idx;
+
+    for (i = 0; i < def->nrngs; i++) {
+        if ((idx = qemuDomainDeviceAliasIndex(&def->rngs[i]->info, "rng")) >= maxidx)
+            maxidx = idx + 1;
+    }
+
+    if (virAsprintf(&rng->info.alias, "rng%d", maxidx) < 0)
         return -1;
 
     return 0;
@@ -480,7 +489,7 @@ qemuAssignDeviceAliases(virDomainDefPtr def, virQEMUCapsPtr qemuCaps)
             return -1;
     }
     for (i = 0; i < def->nrngs; i++) {
-        if (qemuAssignDeviceRNGAlias(def->rngs[i], i) < 0)
+        if (virAsprintf(&def->rngs[i]->info.alias, "rng%zu", i) < 0)
             return -1;
     }
     if (def->tpm) {

src/qemu/qemu_alias.h

@@ -54,8 +54,8 @@ int qemuAssignDeviceRedirdevAlias(virDomainDefPtr def,
                                   virDomainRedirdevDefPtr redirdev,
                                   int idx);
 
-int qemuAssignDeviceRNGAlias(virDomainRNGDefPtr rng,
-                             size_t idx);
+int qemuAssignDeviceRNGAlias(virDomainDefPtr def,
+                             virDomainRNGDefPtr rng);
 
 int qemuAssignDeviceAliases(virDomainDefPtr def, virQEMUCapsPtr qemuCaps);
 

src/qemu/qemu_hotplug.c

@@ -1625,7 +1625,7 @@ qemuDomainAttachRNGDevice(virQEMUDriverPtr driver,
     const char *type;
     int ret = -1;
 
-    if (qemuAssignDeviceRNGAlias(rng, vm->def->nrngs) < 0)
+    if (qemuAssignDeviceRNGAlias(vm->def, rng) < 0)
         return -1;
 
     /* preallocate space for the device definition */