savevm: Fix no_migrate

The no_migrate save state flag is currently only checked in the
last phase of migration.  This means that we potentially waste
a lot of time and bandwidth with the live state handlers before
we ever check the no_migrate flags.  The error message printed
when we catch a non-migratable device doesn't get printed for
a detached migration.  And, no_migrate does nothing to prevent
an incoming migration to a target that includes a non-migratable
device.  This attempts to fix all of these.

One notable difference in behavior is that an outgoing migration
now checks for non-migratable devices before ever connecting to
the target system.  This means the target will remain listening
rather than exit from failure.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

migration.c

@@ -88,6 +88,10 @@ int do_migrate(Monitor *mon, const QDict *qdict, QObject **ret_data)
         return -1;
     }
 
+    if (qemu_savevm_state_blocked(mon)) {
+        return -1;
+    }
+
     if (strstart(uri, "tcp:", &p)) {
         s = tcp_start_outgoing_migration(mon, p, max_throttle, detach,
                                          blk, inc);

savevm.c

@@ -1401,19 +1401,13 @@ static int vmstate_load(QEMUFile *f, SaveStateEntry *se, int version_id)
     return vmstate_load_state(f, se->vmsd, se->opaque, version_id);
 }
 
-static int vmstate_save(QEMUFile *f, SaveStateEntry *se)
+static void vmstate_save(QEMUFile *f, SaveStateEntry *se)
 {
-    if (se->no_migrate) {
-        return -1;
-    }
-
     if (!se->vmsd) {         /* Old style */
         se->save_state(f, se->opaque);
-        return 0;
+        return;
     }
     vmstate_save_state(f,se->vmsd, se->opaque);
-
-    return 0;
 }
 
 #define QEMU_VM_FILE_MAGIC           0x5145564d
@@ -1427,6 +1421,20 @@ static int vmstate_save(QEMUFile *f, SaveStateEntry *se)
 #define QEMU_VM_SECTION_FULL         0x04
 #define QEMU_VM_SUBSECTION           0x05
 
+bool qemu_savevm_state_blocked(Monitor *mon)
+{
+    SaveStateEntry *se;
+
+    QTAILQ_FOREACH(se, &savevm_handlers, entry) {
+        if (se->no_migrate) {
+            monitor_printf(mon, "state blocked by non-migratable device '%s'\n",
+                           se->idstr);
+            return true;
+        }
+    }
+    return false;
+}
+
 int qemu_savevm_state_begin(Monitor *mon, QEMUFile *f, int blk_enable,
                             int shared)
 {
@@ -1508,7 +1516,6 @@ int qemu_savevm_state_iterate(Monitor *mon, QEMUFile *f)
 int qemu_savevm_state_complete(Monitor *mon, QEMUFile *f)
 {
     SaveStateEntry *se;
-    int r;
 
     cpu_synchronize_all_states();
 
@@ -1541,11 +1548,7 @@ int qemu_savevm_state_complete(Monitor *mon, QEMUFile *f)
         qemu_put_be32(f, se->instance_id);
         qemu_put_be32(f, se->version_id);
 
-        r = vmstate_save(f, se);
-        if (r < 0) {
-            monitor_printf(mon, "cannot migrate with device '%s'\n", se->idstr);
-            return r;
-        }
+        vmstate_save(f, se);
     }
 
     qemu_put_byte(f, QEMU_VM_EOF);
@@ -1575,6 +1578,11 @@ static int qemu_savevm_state(Monitor *mon, QEMUFile *f)
     saved_vm_running = vm_running;
     vm_stop(0);
 
+    if (qemu_savevm_state_blocked(mon)) {
+        ret = -EINVAL;
+        goto out;
+    }
+
     ret = qemu_savevm_state_begin(mon, f, 0, 0);
     if (ret < 0)
         goto out;
@@ -1692,6 +1700,10 @@ int qemu_loadvm_state(QEMUFile *f)
     unsigned int v;
     int ret;
 
+    if (qemu_savevm_state_blocked(default_mon)) {
+        return -EINVAL;
+    }
+
     v = qemu_get_be32(f);
     if (v != QEMU_VM_FILE_MAGIC)
         return -EINVAL;

sysemu.h

@@ -75,6 +75,7 @@ void qemu_announce_self(void);
 
 void main_loop_wait(int nonblocking);
 
+bool qemu_savevm_state_blocked(Monitor *mon);
 int qemu_savevm_state_begin(Monitor *mon, QEMUFile *f, int blk_enable,
                             int shared);
 int qemu_savevm_state_iterate(Monitor *mon, QEMUFile *f);