qemu: hotplug: Properly recalculate/reload balloon size after hot(un)plug

Rather than trying some magic calculations on our side query the monitor
for the current size of the memory balloon both on hotplug and
hotunplug.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1220702

src/qemu/qemu_hotplug.c

@@ -33,6 +33,7 @@
 #include "qemu_command.h"
 #include "qemu_hostdev.h"
 #include "qemu_interface.h"
+#include "qemu_process.h"
 #include "domain_audit.h"
 #include "netdev_bandwidth_conf.h"
 #include "domain_nwfilter.h"
@@ -1742,7 +1743,6 @@ qemuDomainAttachMemory(virQEMUDriverPtr driver,
     const char *backendType;
     virJSONValuePtr props = NULL;
     virObjectEventPtr event;
-    bool fix_balloon = false;
     int id;
     int ret = -1;
 
@@ -1757,9 +1757,6 @@ 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)))
         goto cleanup;
 
@@ -1800,9 +1797,8 @@ qemuDomainAttachMemory(virQEMUDriverPtr driver,
     event = virDomainEventDeviceAddedNewFromObj(vm, objalias);
     qemuDomainEventQueue(driver, event);
 
-    /* fix the balloon size if it was set to maximum */
-    if (fix_balloon)
-        vm->def->mem.cur_balloon += mem->size;
+    /* fix the balloon size */
+    ignore_value(qemuProcessRefreshBalloonState(driver, vm, QEMU_ASYNC_JOB_NONE));
 
     /* mem is consumed by vm->def */
     mem = NULL;
@@ -2938,13 +2934,14 @@ qemuDomainRemoveMemoryDevice(virQEMUDriverPtr driver,
     if (rc < 0)
         return -1;
 
-    vm->def->mem.cur_balloon -= mem->size;
-
     if ((idx = virDomainMemoryFindByDef(vm->def, mem)) >= 0)
         virDomainMemoryRemove(vm->def, idx);
 
     virDomainMemoryDefFree(mem);
 
+    /* fix the balloon size */
+    ignore_value(qemuProcessRefreshBalloonState(driver, vm, QEMU_ASYNC_JOB_NONE));
+
     /* decrease the mlock limit after memory unplug if necessary */
     ignore_value(qemuDomainAdjustMaxMemLock(vm));
 

src/qemu/qemu_process.c

@@ -1993,7 +1993,7 @@ qemuRefreshVirtioChannelState(virQEMUDriverPtr driver,
 }
 
 
-static int
+int
 qemuProcessRefreshBalloonState(virQEMUDriverPtr driver,
                                virDomainObjPtr vm,
                                int asyncJob)

src/qemu/qemu_process.h

@@ -193,4 +193,8 @@ int qemuProcessSetupIOThread(virDomainObjPtr vm,
 
 int qemuRefreshVirtioChannelState(virQEMUDriverPtr driver,
                                   virDomainObjPtr vm);
+
+int qemuProcessRefreshBalloonState(virQEMUDriverPtr driver,
+                                   virDomainObjPtr vm,
+                                   int asyncJob);
 #endif /* __QEMU_PROCESS_H__ */