migration: disallow migrate_add_blocker during migration

If a migration is already in progress and somebody attempts
to add a migration blocker, this should rightly fail.

Add an errp parameter and a retcode return value to migrate_add_blocker.

Signed-off-by: John Snow <jsnow@redhat.com>
Signed-off-by: Ashijeet Acharya <ashijeetacharya@gmail.com>
Message-Id: <1484566314-3987-5-git-send-email-ashijeetacharya@gmail.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Acked-by: Greg Kurz <groug@kaod.org>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
  Merged with recent 'Allow invtsc migration' change

1 files changed, 12 insertions, 7 deletions

diff --git a/block/vvfat.c b/block/vvfat.c
index 7b706dc346..c6bf67e8f3 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -1185,21 +1185,26 @@ static int vvfat_open(BlockDriverState *bs, QDict *options, int flags,
 
     s->sector_count = s->faked_sectors + s->sectors_per_cluster*s->cluster_count;
 
-    if (s->first_sectors_number == 0x40) {
-        init_mbr(s, cyls, heads, secs);
-    }
-
-    qemu_co_mutex_init(&s->lock);
-
     /* Disable migration when vvfat is used rw */
     if (s->qcow) {
         error_setg(&s->migration_blocker,
                    "The vvfat (rw) format used by node '%s' "
                    "does not support live migration",
                    bdrv_get_device_or_node_name(bs));
-        migrate_add_blocker(s->migration_blocker);
+        ret = migrate_add_blocker(s->migration_blocker, &local_err);
+        if (local_err) {
+            error_propagate(errp, local_err);
+            error_free(s->migration_blocker);
+            goto fail;
+        }
     }
 
+    if (s->first_sectors_number == 0x40) {
+        init_mbr(s, cyls, heads, secs);
+    }
+
+    qemu_co_mutex_init(&s->lock);
+
     ret = 0;
 fail:
     qemu_opts_del(opts);