[libvirt PATCH 4/4] qemu: Enable migration events only for fresh QEMU process

[Jiri Denemark]

Every running QEMU process we are willing to reconnect (i.e., at least
3.1.0) supports migration events and we can assume the capability is
already enabled since last time libvirt daemon connected to its monitor.

Well, it's not guaranteed though. If libvirt 1.2.17 or older was used to
start QEMU 3.1.0 or newer, migration events would not be enabled. And if
the user decides to upgrade libvirt from 1.2.17 to 8.4.0 while the QEMU
process is still running, they would not be able to migrate the domain
because of disabled migration events. I think we do not really need to
worry about this scenario as libvirt 1.2.17 is 7 years old while QEMU
3.1.0 was released only 3.5 years ago. Thus a chance someone would be
running such configuration should be fairly small and a combination with
upgrading 1.2.17 to 8.4.0 (or newer) with running domains should get it
pretty much to zero. The issue would disappear ff the ancient libvirt is
first upgraded to something older than 8.4.0 and then to the current
libvirt.

Signed-off-by: Jiri Denemark <jdenemar at redhat.com>
---

Notes:
    I was hoping we could do this without any downside, but it appeared this
    was not possible. In case someone still thinks this would be an issue, I
    can take an alternative solution and check whether migration events are
    enabled when reconnecting to QEMU monitor.

 src/qemu/qemu_migration_params.c | 26 ++++++++++++++------------
 src/qemu/qemu_migration_params.h |  3 ++-
 src/qemu/qemu_process.c          | 14 +++++++++-----
 3 files changed, 25 insertions(+), 18 deletions(-)

diff --git a/src/qemu/qemu_migration_params.c b/src/qemu/qemu_migration_params.c
index 26754f03f8..95fd773645 100644
--- a/src/qemu/qemu_migration_params.c
+++ b/src/qemu/qemu_migration_params.c
@@ -1385,10 +1385,10 @@ qemuMigrationParamsParse(xmlXPathContextPtr ctxt,
 int
 qemuMigrationCapsCheck(virQEMUDriver *driver,
                        virDomainObj *vm,
-                       int asyncJob)
+                       int asyncJob,
+                       bool reconnect)
 {
     qemuDomainObjPrivate *priv = vm->privateData;
-    g_autoptr(virBitmap) migEvent = NULL;
     g_autoptr(virJSONValue) json = NULL;
     g_auto(GStrv) caps = NULL;
     char **capStr;
@@ -1419,22 +1419,24 @@ qemuMigrationCapsCheck(virQEMUDriver *driver,
         }
     }
 
-    migEvent = virBitmapNew(QEMU_MIGRATION_CAP_LAST);
+    if (!reconnect) {
+        g_autoptr(virBitmap) migEvent = virBitmapNew(QEMU_MIGRATION_CAP_LAST);
 
-    ignore_value(virBitmapSetBit(migEvent, QEMU_MIGRATION_CAP_EVENTS));
+        ignore_value(virBitmapSetBit(migEvent, QEMU_MIGRATION_CAP_EVENTS));
 
-    if (!(json = qemuMigrationCapsToJSON(migEvent, migEvent)))
-        return -1;
+        if (!(json = qemuMigrationCapsToJSON(migEvent, migEvent)))
+            return -1;
 
-    if (qemuDomainObjEnterMonitorAsync(driver, vm, asyncJob) < 0)
-        return -1;
+        if (qemuDomainObjEnterMonitorAsync(driver, vm, asyncJob) < 0)
+            return -1;
 
-    rc = qemuMonitorSetMigrationCapabilities(priv->mon, &json);
+        rc = qemuMonitorSetMigrationCapabilities(priv->mon, &json);
 
-    qemuDomainObjExitMonitor(vm);
+        qemuDomainObjExitMonitor(vm);
 
-    if (rc < 0)
-        return -1;
+        if (rc < 0)
+            return -1;
+    }
 
     /* Migration events capability must always be enabled, clearing it from
      * migration capabilities bitmap makes sure it won't be touched anywhere
diff --git a/src/qemu/qemu_migration_params.h b/src/qemu/qemu_migration_params.h
index 4a8815e776..a0909b9f3d 100644
--- a/src/qemu/qemu_migration_params.h
+++ b/src/qemu/qemu_migration_params.h
@@ -162,7 +162,8 @@ qemuMigrationParamsParse(xmlXPathContextPtr ctxt,
 int
 qemuMigrationCapsCheck(virQEMUDriver *driver,
                        virDomainObj *vm,
-                       int asyncJob);
+                       int asyncJob,
+                       bool reconnect);
 
 bool
 qemuMigrationCapsGet(virDomainObj *vm,
diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index 2b16298942..fd4db43a42 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -1914,8 +1914,12 @@ qemuProcessInitMonitor(virQEMUDriver *driver,
 
 
 static int
-qemuConnectMonitor(virQEMUDriver *driver, virDomainObj *vm, int asyncJob,
-                   bool retry, qemuDomainLogContext *logCtxt)
+qemuConnectMonitor(virQEMUDriver *driver,
+                   virDomainObj *vm,
+                   int asyncJob,
+                   bool retry,
+                   qemuDomainLogContext *logCtxt,
+                   bool reconnect)
 {
     qemuDomainObjPrivate *priv = vm->privateData;
     qemuMonitor *mon = NULL;
@@ -1968,7 +1972,7 @@ qemuConnectMonitor(virQEMUDriver *driver, virDomainObj *vm, int asyncJob,
     if (qemuProcessInitMonitor(driver, vm, asyncJob) < 0)
         return -1;
 
-    if (qemuMigrationCapsCheck(driver, vm, asyncJob) < 0)
+    if (qemuMigrationCapsCheck(driver, vm, asyncJob, reconnect) < 0)
         return -1;
 
     return 0;
@@ -2353,7 +2357,7 @@ qemuProcessWaitForMonitor(virQEMUDriver *driver,
     VIR_DEBUG("Connect monitor to vm=%p name='%s' retry=%d",
               vm, vm->def->name, retry);
 
-    if (qemuConnectMonitor(driver, vm, asyncJob, retry, logCtxt) < 0)
+    if (qemuConnectMonitor(driver, vm, asyncJob, retry, logCtxt, false) < 0)
         goto cleanup;
 
     /* Try to get the pty path mappings again via the monitor. This is much more
@@ -8773,7 +8777,7 @@ qemuProcessReconnect(void *opaque)
     tryMonReconn = true;
 
     /* XXX check PID liveliness & EXE path */
-    if (qemuConnectMonitor(driver, obj, VIR_ASYNC_JOB_NONE, retry, NULL) < 0)
+    if (qemuConnectMonitor(driver, obj, VIR_ASYNC_JOB_NONE, retry, NULL, true) < 0)
         goto error;
 
     priv->machineName = qemuDomainGetMachineName(obj);
-- 
2.35.1