qemu: Fix balloon size handling with memory hot(un)plug

Since libvirt doesn't call to update the new balloon size in qemu add
code that will handle tweaking of the size of the current balloon
statistic until qemu reports the new size using the event.

src/qemu/qemu_driver.c

@@ -8373,6 +8373,9 @@ qemuDomainAttachDeviceConfig(virQEMUCapsPtr qemuCaps,
             return -1;
         }
 
+        if (vmdef->mem.cur_balloon == virDomainDefGetMemoryActual(vmdef))
+            vmdef->mem.cur_balloon += dev->data.memory->size;
+
         if (virDomainMemoryInsert(vmdef, dev->data.memory) < 0)
             return -1;
         dev->data.memory = NULL;

src/qemu/qemu_hotplug.c

@@ -1726,6 +1726,7 @@ qemuDomainAttachMemory(virQEMUDriverPtr driver,
     const char *backendType;
     virJSONValuePtr props = NULL;
     virObjectEventPtr event;
+    bool fix_balloon = false;
     int id;
     int ret = -1;
 
@@ -1741,6 +1742,9 @@ qemuDomainAttachMemory(virQEMUDriverPtr driver,
     if (virAsprintf(&objalias, "mem%s", mem->info.alias) < 0)
         goto cleanup;
 
+    if (vm->def->mem.cur_balloon == virDomainDefGetMemoryActual(vm->def))
+        fix_balloon = true;
+
     if (!(devstr = qemuBuildMemoryDeviceStr(mem, vm->def, priv->qemuCaps)))
         goto cleanup;
 
@@ -1779,6 +1783,10 @@ qemuDomainAttachMemory(virQEMUDriverPtr driver,
     if (event)
         qemuDomainEventQueue(driver, event);
 
+    /* fix the balloon size if it was set to maximum */
+    if (fix_balloon)
+        vm->def->mem.cur_balloon += mem->size;
+
     /* mem is consumed by vm->def */
     mem = NULL;
 
@@ -2896,6 +2904,8 @@ qemuDomainRemoveMemoryDevice(virQEMUDriverPtr driver,
     if (qemuDomainObjExitMonitor(driver, vm) < 0 || rc < 0)
         goto error;
 
+    vm->def->mem.cur_balloon -= mem->size;
+
     if ((idx = virDomainMemoryFindByDef(vm->def, mem)) >= 0)
         virDomainMemoryRemove(vm->def, idx);