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, 22 insertions, 11 deletions

diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
index fa58877..06b6e7e 100644
--- a/hw/9pfs/9p.c
+++ b/hw/9pfs/9p.c
@@ -979,6 +979,7 @@ static void coroutine_fn v9fs_attach(void *opaque)
     size_t offset = 7;
     V9fsQID qid;
     ssize_t err;
+    Error *local_err = NULL;
 
     v9fs_string_init(&uname);
     v9fs_string_init(&aname);
@@ -1007,26 +1008,36 @@ static void coroutine_fn v9fs_attach(void *opaque)
         clunk_fid(s, fid);
         goto out;
     }
-    err = pdu_marshal(pdu, offset, "Q", &qid);
-    if (err < 0) {
-        clunk_fid(s, fid);
-        goto out;
-    }
-    err += offset;
-    memcpy(&s->root_qid, &qid, sizeof(qid));
-    trace_v9fs_attach_return(pdu->tag, pdu->id,
-                             qid.type, qid.version, qid.path);
+
     /*
      * disable migration if we haven't done already.
      * attach could get called multiple times for the same export.
      */
     if (!s->migration_blocker) {
-        s->root_fid = fid;
         error_setg(&s->migration_blocker,
                    "Migration is disabled when VirtFS export path '%s' is mounted in the guest using mount_tag '%s'",
                    s->ctx.fs_root ? s->ctx.fs_root : "NULL", s->tag);
-        migrate_add_blocker(s->migration_blocker);
+        err = migrate_add_blocker(s->migration_blocker, &local_err);
+        if (local_err) {
+            error_free(local_err);
+            error_free(s->migration_blocker);
+            s->migration_blocker = NULL;
+            clunk_fid(s, fid);
+            goto out;
+        }
+        s->root_fid = fid;
+    }
+
+    err = pdu_marshal(pdu, offset, "Q", &qid);
+    if (err < 0) {
+        clunk_fid(s, fid);
+        goto out;
     }
+    err += offset;
+
+    memcpy(&s->root_qid, &qid, sizeof(qid));
+    trace_v9fs_attach_return(pdu->tag, pdu->id,
+                             qid.type, qid.version, qid.path);
 out:
     put_fid(pdu, fidp);
 out_nofid: