[PATCH v2 25/27] tools/libxl: Handle checkpoint records in a libxl migration v2 stream

[Andrew Cooper <andrew.cooper3@citrix.com>]

This is the final bit of untangling for Remus.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
CC: Ian Campbell <Ian.Campbell@citrix.com>
CC: Ian Jackson <Ian.Jackson@eu.citrix.com>
CC: Wei Liu <wei.liu2@citrix.com>

---
As before, Remus functionality is untested, but the new logic here should
handle failovers correctly.  The patch has changed greatly from v1, both in a
functional sence, and because of the knockon effects from earlier changes.
---
 tools/libxl/libxl_create.c      |   27 +++++++++++
 tools/libxl/libxl_internal.h    |    8 ++++
 tools/libxl/libxl_stream_read.c |   97 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 132 insertions(+)

diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
index 2a0063a..0325bf1 100644
--- a/tools/libxl/libxl_create.c
+++ b/tools/libxl/libxl_create.c
@@ -672,6 +672,29 @@ static int store_libxl_entry(libxl__gc *gc, uint32_t domid,
         libxl_device_model_version_to_string(b_info->device_model_version));
 }
 
+/*----- remus asynchronous checkpoint callback -----*/
+
+static void remus_checkpoint_stream_done(
+    libxl__egc *egc, libxl__stream_read_state *srs, int rc);
+
+static void libxl__remus_domain_checkpoint_callback(void *data)
+{
+    libxl__save_helper_state *shs = data;
+    libxl__domain_create_state *dcs = CONTAINER_OF(shs, *dcs, shs);
+    libxl__egc *egc = dcs->shs.egc;
+    STATE_AO_GC(dcs->ao);
+
+    libxl__stream_read_start_checkpoint(egc, &dcs->srs);
+}
+
+static void remus_checkpoint_stream_done(
+    libxl__egc *egc, libxl__stream_read_state *srs, int rc)
+{
+    libxl__domain_create_state *dcs = CONTAINER_OF(srs, *dcs, srs);
+
+    libxl__xc_domain_saverestore_async_callback_done(egc, &dcs->shs, rc);
+}
+
 /*----- main domain creation -----*/
 
 /* We have a linear control flow; only one event callback is
@@ -939,6 +962,8 @@ static void domcreate_bootloader_done(libxl__egc *egc,
     libxl_domain_config *const d_config = dcs->guest_config;
     const int restore_fd = dcs->restore_fd;
     libxl__domain_build_state *const state = &dcs->build_state;
+    libxl__srm_restore_autogen_callbacks *const callbacks =
+        &dcs->shs.callbacks.restore.a;
 
     if (rc) {
         domcreate_rebuild_done(egc, dcs, rc);
@@ -966,6 +991,7 @@ static void domcreate_bootloader_done(libxl__egc *egc,
     }
 
     /* Restore */
+    callbacks->checkpoint = libxl__remus_domain_checkpoint_callback;
 
     rc = libxl__build_pre(gc, domid, d_config, state);
     if (rc)
@@ -975,6 +1001,7 @@ static void domcreate_bootloader_done(libxl__egc *egc,
     dcs->srs.fd = restore_fd;
     dcs->srs.legacy = (dcs->restore_params.stream_version == 1);
     dcs->srs.completion_callback = domcreate_stream_done;
+    dcs->srs.checkpoint_callback = remus_checkpoint_stream_done;
 
     libxl__stream_read_start(egc, &dcs->srs);
     return;
diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 84e22c2..1b62f25 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -3332,9 +3332,13 @@ struct libxl__stream_read_state {
     void (*completion_callback)(libxl__egc *egc,
                                 libxl__stream_read_state *srs,
                                 int rc);
+    void (*checkpoint_callback)(libxl__egc *egc,
+                                libxl__stream_read_state *srs,
+                                int rc);
     /* Private */
     int rc;
     bool running;
+    bool in_checkpoint;
 
     /* Active-stuff handling */
     int joined_rc;
@@ -3349,6 +3353,8 @@ struct libxl__stream_read_state {
     LIBXL_STAILQ_HEAD(, libxl__sr_record_buf) record_queue;
     enum {
         SRS_PHASE_NORMAL,
+        SRS_PHASE_BUFFERING,
+        SRS_PHASE_UNBUFFERING,
     } phase;
     bool recursion_guard;
 
@@ -3362,6 +3368,8 @@ _hidden void libxl__stream_read_start(libxl__egc *egc,
 
 _hidden void libxl__stream_read_continue(libxl__egc *egc,
                                          libxl__stream_read_state *stream);
+_hidden void libxl__stream_read_start_checkpoint(
+    libxl__egc *egc, libxl__stream_read_state *stream);
 
 _hidden void libxl__stream_read_abort(libxl__egc *egc,
                                       libxl__stream_read_state *stream, int rc);
diff --git a/tools/libxl/libxl_stream_read.c b/tools/libxl/libxl_stream_read.c
index 81095cd..6cfa05c 100644
--- a/tools/libxl/libxl_stream_read.c
+++ b/tools/libxl/libxl_stream_read.c
@@ -123,6 +123,10 @@ static int setup_read(libxl__stream_read_state *stream,
     return libxl__datacopier_start(dc);
 }
 
+/* Error handling for checkpoint mini-loop. */
+static void checkpoint_done(libxl__egc *egc,
+                            libxl__stream_read_state *stream, int rc);
+
 void libxl__stream_read_start(libxl__egc *egc,
                               libxl__stream_read_state *stream)
 {
@@ -186,6 +190,18 @@ void libxl__stream_read_start(libxl__egc *egc,
     stream_failed(egc, stream, ret);
 }
 
+void libxl__stream_read_start_checkpoint(libxl__egc *egc,
+                                         libxl__stream_read_state *stream)
+{
+    assert(stream->running);
+    assert(!stream->in_checkpoint);
+
+    stream->in_checkpoint = true;
+    stream->phase = SRS_PHASE_BUFFERING;
+
+    setup_read_record(egc, stream);
+}
+
 void libxl__stream_read_abort(libxl__egc *egc,
                               libxl__stream_read_state *stream, int rc)
 {
@@ -206,6 +222,16 @@ static void stream_failed(libxl__egc *egc,
     stream->rc = rc;
 
     if (stream->running) {
+
+        /*
+         * If we are in a checkpoint, pass the failure to libxc, which will
+         * come back around to us via libxl__xc_domain_restore_done().
+         */
+        if (stream->in_checkpoint) {
+            checkpoint_done(egc, stream, rc);
+            return;
+        }
+
         stream_done(egc, stream);
     }
 }
@@ -215,6 +241,7 @@ static void stream_done(libxl__egc *egc,
 {
     libxl__sr_record_buf *rec, *trec;
 
+    assert(!stream->in_checkpoint);
     assert(stream->running);
     stream->running = false;
 
@@ -296,6 +323,8 @@ static void stream_continue(libxl__egc *egc,
          * processing the record.  At no point should there ever be two
          * records in the queue.
          */
+        assert(!stream->in_checkpoint);
+
         if (LIBXL_STAILQ_EMPTY(&stream->record_queue))
             setup_read_record(egc, stream);
         else {
@@ -304,6 +333,45 @@ static void stream_continue(libxl__egc *egc,
         }
         break;
 
+    case SRS_PHASE_BUFFERING: {
+        /*
+         * Buffer phase of a checkpoint in the stream.  Collect records read
+         * from the stream without processing them.  We need to peek at the
+         * tail to spot the CHECKPOINT_END record, and switch to the
+         * unbuffering phase.
+         */
+        libxl__sr_record_buf *rec = LIBXL_STAILQ_LAST(
+            &stream->record_queue, libxl__sr_record_buf, entry);
+
+        assert(stream->in_checkpoint);
+
+        if ( !rec || rec->hdr.type != REC_TYPE_CHECKPOINT_END ) {
+            setup_read_record(egc, stream);
+            break;
+        }
+
+        /*
+         * There are now some number of buffered records, with a
+         * CHECKPOINT_END at the end. Start processing them all.
+         */
+        stream->phase = SRS_PHASE_UNBUFFERING;
+    }
+        /* FALLTHROUGH */
+    case SRS_PHASE_UNBUFFERING:
+        /*
+         * Unbuffering phase of a checkpoint in the stream.  Process all
+         * records collected during the buffering phase.
+         */
+        assert(stream->in_checkpoint);
+
+        while (process_record(egc, stream))
+            ; /*
+               * Nothing! process_record() helpfully tells us if no specific
+               * futher actions have been set up, in which case we want to go
+               * ahead and process the next record.
+               */
+        break;
+
     default:
         abort();
     }
@@ -528,6 +596,15 @@ static bool process_record(libxl__egc *egc,
         write_emulator_blob(egc, stream, rec);
         break;
 
+    case REC_TYPE_CHECKPOINT_END:
+        if (!stream->in_checkpoint) {
+            LOG(ERROR, "Unexpected CHECKPOINT_END record in stream");
+            ret = ERROR_FAIL;
+            goto err;
+        }
+        checkpoint_done(egc, stream, 0);
+        break;
+
     default:
         LOG(ERROR, "Unrecognised record 0x%08x", rec->hdr.type);
         ret = ERROR_FAIL;
@@ -625,6 +702,26 @@ static void write_emulator_done(libxl__egc *egc,
     stream_failed(egc, stream, ret);
 }
 
+static void checkpoint_done(libxl__egc *egc,
+                            libxl__stream_read_state *stream, int rc)
+{
+    int ret;
+
+    assert(stream->in_checkpoint);
+
+    if (rc == 0)
+        ret = 0; /* Success */
+    else if (stream->phase == SRS_PHASE_BUFFERING)
+        ret = 2; /* Failover */
+    else
+        ret = 1; /* Error (fatal) */
+
+    stream->checkpoint_callback(egc, stream, ret);
+
+    stream->in_checkpoint = false;
+    stream->phase = SRS_PHASE_NORMAL;
+}
+
 /*
  * Local variables:
  * mode: C
-- 
1.7.10.4