migration: allow dst vm pause on postcopy

When there is IO error on the incoming channel (e.g., network down),
instead of bailing out immediately, we allow the dst vm to switch to the
new POSTCOPY_PAUSE state. Currently it is still simple - it waits the
new semaphore, until someone poke it for another attempt.

One note is that here on ram loading thread we cannot detect the
POSTCOPY_ACTIVE state, but we need to detect the more specific
POSTCOPY_INCOMING_RUNNING state, to make sure we have already loaded all
the device states.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20180502104740.12123-5-peterx@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/migration/migration.h b/migration/migration.h
index 60283c39b2..0ccdcb8ffe 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -73,6 +73,9 @@ struct MigrationIncomingState {
      * live migration, to calculate vCPU block time
      * */
     struct PostcopyBlocktimeContext *blocktime_ctx;
+
+    /* notify PAUSED postcopy incoming migrations to try to continue */
+    QemuSemaphore postcopy_pause_sem_dst;
 };
 
 MigrationIncomingState *migration_incoming_get_current(void);