libxl: Remus - suspend/postflush/commit callbacks

 * Add libxl callback functions for Remus checkpoint suspend, postflush
   (aka resume) and checkpoint commit callbacks.
 * suspend callback is a stub that just bounces off
   libxl__domain_suspend_common_callback - which suspends the domain and
   saves the devices model state to a file.
 * resume callback currently just resumes the domain (and the device model).
 * commit callback just writes out the saved device model state to the
   network and sleeps for the checkpoint interval.
 * Introduce a new public API, libxl_domain_remus_start (currently a stub)
   that sets up the network and disk buffer and initiates continuous
   checkpointing.

 * Future patches will augment these callbacks/functions with more functionalities
   like issuing network buffer plug/unplug commands, disk checkpoint commands, etc.

Signed-off-by: Shriram Rajagopalan <rshriram@cs.ubc.ca>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Ian Campbell <ian.campbell@citrix.com>

1 files changed, 21 insertions, 2 deletions

diff --git a/tools/libxc/xenguest.h b/tools/libxc/xenguest.h
index 6435f659af..91d53f7426 100644
--- a/tools/libxc/xenguest.h
+++ b/tools/libxc/xenguest.h
@@ -33,10 +33,29 @@
 
 /* callbacks provided by xc_domain_save */
 struct save_callbacks {
+    /* Called after expiration of checkpoint interval,
+     * to suspend the guest.
+     */
     int (*suspend)(void* data);
-    /* callback to rendezvous with external checkpoint functions */
+
+    /* Called after the guest's dirty pages have been
+     *  copied into an output buffer.
+     * Callback function resumes the guest & the device model,
+     *  returns to xc_domain_save.
+     * xc_domain_save then flushes the output buffer, while the
+     *  guest continues to run.
+     */
     int (*postcopy)(void* data);
-    /* returns:
+
+    /* Called after the memory checkpoint has been flushed
+     * out into the network. Typical actions performed in this
+     * callback include:
+     *   (a) send the saved device model state (for HVM guests),
+     *   (b) wait for checkpoint ack
+     *   (c) release the network output buffer pertaining to the acked checkpoint.
+     *   (c) sleep for the checkpoint interval.
+     *
+     * returns:
      * 0: terminate checkpointing gracefully
      * 1: take another checkpoint */
     int (*checkpoint)(void* data);