block/mirror: Make cancel always cancel pre-READY

Commit b76e4458 made the mirror block
job respect block-job-cancel's @force flag: With that flag set, it would
now always really cancel, even post-READY.

Unfortunately, it had a side effect: Without that flag set, it would now
never cancel, not even before READY.  Considering that is an
incompatible change and not noted anywhere in the commit or the
description of block-job-cancel's @force parameter, this seems
unintentional and we should revert to the previous behavior, which is to
immediately cancel the job when block-job-cancel is called before source
and target are in sync (i.e. before the READY event).

Cc: qemu-stable@nongnu.org
Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1572856Reported-by: NYanan Fu <yfu@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Message-id: 20180501220509.14152-2-mreitz@redhat.com
Reviewed-by: NJeff Cody <jcody@redhat.com>
Signed-off-by: NJeff Cody <jcody@redhat.com>

block/mirror.c

@@ -874,7 +874,9 @@ static void coroutine_fn mirror_run(void *opaque)
         }
         trace_mirror_before_sleep(s, cnt, s->synced, delay_ns);
         block_job_sleep_ns(&s->common, delay_ns);
-        if (block_job_is_cancelled(&s->common) && s->common.force) {
+        if (block_job_is_cancelled(&s->common) &&
+            (!s->synced || s->common.force))
+        {
             break;
         }
         s->last_pause_ns = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);