[PATCH v4 27/29] 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.

When libxc issues a checkpoint callback, start reading and buffering
all libxl records from the stream.  Once a CHECKPOINT_END record is
encountered, start processing all records.

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

---
v3: Simplify, use named constants for API
---
 tools/libxl/libxl_create.c      |   25 ++++++++
 tools/libxl/libxl_internal.h    |    8 +++
 tools/libxl/libxl_stream_read.c |  123 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 156 insertions(+)

diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
index c51d64f..5b4d333 100644
--- a/tools/libxl/libxl_create.c
+++ b/tools/libxl/libxl_create.c
@@ -672,6 +672,27 @@ 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 = shs->caller_state;
+    libxl__egc *egc = 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 *stream, int rc)
+{
+    libxl__xc_domain_saverestore_async_callback_done(egc, &stream->shs, rc);
+}
+
 /*----- main domain creation -----*/
 
 /* We have a linear control flow; only one event callback is
@@ -939,6 +960,8 @@ 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->srs.shs.callbacks.restore.a;
 
     if (rc) {
         domcreate_rebuild_done(egc, dcs, rc);
@@ -966,6 +989,7 @@ 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)
@@ -976,6 +1000,7 @@ 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 9961a53..7aa4f16 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -3309,9 +3309,13 @@ 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;
     libxl__save_helper_state shs;
     libxl__conversion_helper_state chs;
 
@@ -3321,6 +3325,8 @@ struct libxl__stream_read_state {
     LIBXL_STAILQ_HEAD(, libxl__sr_record_buf) record_queue; /* NOGC */
     enum {
         SRS_PHASE_NORMAL,
+        SRS_PHASE_BUFFERING,
+        SRS_PHASE_UNBUFFERING,
     } phase;
     bool recursion_guard;
 
@@ -3335,6 +3341,8 @@ struct libxl__stream_read_state {
 _hidden void libxl__stream_read_init(libxl__stream_read_state *stream);
 _hidden void libxl__stream_read_start(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);
 static inline bool
diff --git a/tools/libxl/libxl_stream_read.c b/tools/libxl/libxl_stream_read.c
index 3051a2b..2d17403 100644
--- a/tools/libxl/libxl_stream_read.c
+++ b/tools/libxl/libxl_stream_read.c
@@ -35,6 +35,8 @@
  * Undefined    undef  undef        undef       undef    undef
  * Idle         false  undef        false       0        0
  * Active       true   NORMAL       false       0/1      0/partial
+ * Active       true   BUFFERING    true        any      0/partial
+ * Active       true   UNBUFFERING  true        any      0
  *
  * While reading data from the stream, 'dc' is active and a callback
  * is expected.  Most actions in process_record() start a callback of
@@ -46,6 +48,15 @@
  *   Records are read one at time and immediately processed.  (The
  *   record queue will not contain more than a single record.)
  *
+ * PHASE_BUFFERING:
+ *   This phase is used in checkpointed streams, when libxc signals
+ *   the presence of a checkpoint in the stream.  Records are read and
+ *   buffered until a CHECKPOINT_END record has been read.
+ *
+ * PHASE_UNBUFFERING:
+ *   Once a CHECKPOINT_END record has been read, all buffered records
+ *   are processed.
+ *
  * Note:
  *   Record buffers are not allocated from a GC; they are allocated
  *   and tracked manually.  This is to avoid OOM with Remus where the
@@ -57,6 +68,9 @@
  *     - Initialises state.  Must be called once before _start()
  *  - libxl__stream_read_start()
  *     - Starts reading records from the stream, and acting on them.
+ *  - libxl__stream_read_start_checkpoint()
+ *     - Starts buffering records at a checkpoint.  Must be called on
+ *       a running stream.
  *
  * There are several chains of event:
  *
@@ -95,6 +109,8 @@
 /* Success/error/cleanup handling. */
 static void stream_complete(libxl__egc *egc,
                             libxl__stream_read_state *stream, int rc);
+static void checkpoint_done(libxl__egc *egc,
+                            libxl__stream_read_state *stream, int rc);
 static void stream_done(libxl__egc *egc,
                         libxl__stream_read_state *stream);
 static void conversion_done(libxl__egc *egc,
@@ -159,6 +175,7 @@ void libxl__stream_read_init(libxl__stream_read_state *stream)
 {
     stream->rc = 0;
     stream->running = false;
+    stream->in_checkpoint = false;
     libxl__save_helper_init(&stream->shs);
     libxl__conversion_helper_init(&stream->chs);
     FILLZERO(stream->dc);
@@ -225,6 +242,22 @@ void libxl__stream_read_start(libxl__egc *egc,
     stream_complete(egc, stream, rc);
 }
 
+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;
+
+    /*
+     * Libxc has handed control of the fd to us.  Start reading some
+     * libxl records out of it.
+     */
+    stream_continue(egc, stream);
+}
+
 void libxl__stream_read_abort(libxl__egc *egc,
                               libxl__stream_read_state *stream, int rc)
 {
@@ -332,6 +365,54 @@ static void stream_continue(libxl__egc *egc,
         }
         break;
 
+    case SRS_PHASE_BUFFERING: {
+        /*
+         * Buffering phase (checkpointed streams only):
+         *
+         * logically:
+         *   do { read_record(); } while ( not CHECKPOINT_END );
+         *
+         * Read and buffer all records from the stream until a
+         * CHECKPOINT_END record is encountered.  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 (checkpointed streams only):
+         *
+         * logically:
+         *   do { process_record(); } while ( not CHECKPOINT_END );
+         *
+         * 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();
     }
@@ -467,6 +548,15 @@ 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");
+            rc = ERROR_FAIL;
+            goto err;
+        }
+        checkpoint_done(egc, stream, 0);
+        break;
+
     default:
         LOG(ERROR, "Unrecognised record 0x%08x", rec->hdr.type);
         rc = ERROR_FAIL;
@@ -564,17 +654,50 @@ static void stream_complete(libxl__egc *egc,
 {
     assert(stream->running);
 
+    if (stream->in_checkpoint) {
+        assert(rc);
+
+        /*
+         * If an error is encountered while in a checkpoint, pass it
+         * back to libxc.  The failure will come back around to us via
+         * libxl__xc_domain_restore_done()
+         */
+        checkpoint_done(egc, stream, rc);
+        return;
+    }
+
     if (!stream->rc)
         stream->rc = rc;
     stream_done(egc, stream);
 }
 
+static void checkpoint_done(libxl__egc *egc,
+                            libxl__stream_read_state *stream, int rc)
+{
+    int ret;
+
+    assert(stream->in_checkpoint);
+
+    if (rc == 0)
+        ret = XGR_CHECKPOINT_SUCCESS;
+    else if (stream->phase == SRS_PHASE_BUFFERING)
+        ret = XGR_CHECKPOINT_FAILOVER;
+    else
+        ret = XGR_CHECKPOINT_ERROR;
+
+    stream->checkpoint_callback(egc, stream, ret);
+
+    stream->in_checkpoint = false;
+    stream->phase = SRS_PHASE_NORMAL;
+}
+
 static void stream_done(libxl__egc *egc,
                         libxl__stream_read_state *stream)
 {
     libxl__sr_record_buf *rec, *trec;
 
     assert(stream->running);
+    assert(!stream->in_checkpoint);
     stream->running = false;
 
     if (stream->incoming_record)
-- 
1.7.10.4