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Re: [Xen-devel] [PATCH v8 --for 4.6 COLO 08/25] tools/libxl: handle colo_context records in a libxl migration v2 read stream

On 07/16/2015 01:44 AM, Andrew Cooper wrote:
On 15/07/15 10:18, Yang Hongyang wrote:
      if (!stream->rc)
          stream->rc = rc;
      stream_done(egc, stream);
@@ -794,6 +815,36 @@ static void check_all_finished(libxl__egc *egc,
      stream->completion_callback(egc, stream, stream->rc);

+/*----- COLO context handlers -----*/
+void libxl__stream_read_colo_context(libxl__egc *egc,
+                                     libxl__stream_read_state *stream)

A name like this makes the erroneous assumption that a COLO\_CONTEXT
record is what is going to be found next in the stream.

Where and when is a COLO\_CONTEXT record expected, and is it only in the

A COLO CONTEXT is actually a set of control command (I'm not sure command
here is a suitable description) which used to sync the checkpoint steps between
primary and secondary. So it is not only in the back channel.

control_id       0x00000000: Secondary VM is out of sync, start a new checkpoint
                 0x00000001: Secondary VM is suspended
                 0x00000002: Secondary VM is ready
                 0x00000003: Secondary VM is resumed

First boot:
When doing COLO, primary must be start with -p, then start COLO, the
first step is live migration, after migration, when secondary is ready,
we will resume both side.

  control_id      Primary                 Secondary
                  start with -p
                  live migrate
                                          Receive&load state
  0x00000002                              @
                  Resume                  Resume
  0x00000003                              @
                  Start Comparing Packets

At checkpoint:

  control_id      Primary                 Secondary
  0x00000000      @
  0x00000001                              @
                  Send state              Receive state
                  Flush Network           Load state
                  Resume                  Resume
  0x00000003                              @
                  Start Comparing Packets

 1) '@' who sends the message
 2) Every sync-point is synchronized by two sides with only
    one handshake(single direction) for low-latency.
    If more strict synchronization is required, a opposite direction
    sync-point should be added.
 3) Since sync-points are single direction, the remote side may
    go forward a lot when this side just receives the sync-point.

+    assert(stream->running);
+    assert(!stream->in_checkpoint);
+    assert(!stream->in_colo_context);
+    stream->in_colo_context = true;
+    setup_read_record(egc, stream);
+static void handle_colo_context(libxl__egc *egc,
+                                libxl__stream_read_state *stream,
+                                libxl__sr_record_buf *rec)
+    libxl_sr_colo_context *colo_context = rec->body;
+    colo_context_done(egc, stream, colo_context->id);

A handler this trivial should just be done in the switch statement in
process_record().  No need for its own function for a single forward call.




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