[PATCH RFC 16/20] libxl/libxl_stream_write.c: track callback chains with an explicit phase

[Joshua Otto <jtotto@uwaterloo.ca>]

There are three callback chains through libxl_stream_write: the 'normal'
straight-through save path initiated by libxl__stream_write_start(), the
iterated checkpoint path initiated each time by
libxl__stream_write_start_checkpoint(), and the (short) back-channel
checkpoint path initiated by libxl__stream_write_checkpoint_state().
These paths share significant common code but handle failure and
completion slightly differently, so it is necessary to keep track of
the callback chain currently in progress and act accordingly at various
points.

Until now, a collection of booleans in the stream write state has been
used to indicate the current callback chain.  However, the set of
callback chains is really better described by an enum, since only one
callback chain can actually be active at one time.  In anticipation of
the addition of a new chain for postcopy live migration, refactor the
existing logic to use an enum rather than booleans for callback chain
tracking.

No functional change.

Signed-off-by: Joshua Otto <jtotto@uwaterloo.ca>
---
 tools/libxl/libxl_internal.h     |  7 ++-
 tools/libxl/libxl_stream_write.c | 96 ++++++++++++++++++----------------------
 2 files changed, 48 insertions(+), 55 deletions(-)

diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 45d607a..e99d2ef 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -3201,9 +3201,12 @@ struct libxl__stream_write_state {
     /* Private */
     int rc;
     bool running;
-    bool in_checkpoint;
+    enum {
+        SWS_PHASE_NORMAL,
+        SWS_PHASE_CHECKPOINT,
+        SWS_PHASE_CHECKPOINT_STATE
+    } phase;
     bool sync_teardown;  /* Only used to coordinate shutdown on error path. */
-    bool in_checkpoint_state;
     libxl__save_helper_state shs;
 
     /* Main stream-writing data. */
diff --git a/tools/libxl/libxl_stream_write.c b/tools/libxl/libxl_stream_write.c
index c96a6a2..8f2a1c9 100644
--- a/tools/libxl/libxl_stream_write.c
+++ b/tools/libxl/libxl_stream_write.c
@@ -89,12 +89,9 @@ static void emulator_context_read_done(libxl__egc *egc,
                                        int rc, int onwrite, int errnoval);
 static void emulator_context_record_done(libxl__egc *egc,
                                          libxl__stream_write_state *stream);
-static void write_end_record(libxl__egc *egc,
-                             libxl__stream_write_state *stream);
+static void write_phase_end_record(libxl__egc *egc,
+                                   libxl__stream_write_state *stream);
 
-/* Event chain unique to checkpointed streams. */
-static void write_checkpoint_end_record(libxl__egc *egc,
-                                        libxl__stream_write_state *stream);
 static void checkpoint_end_record_done(libxl__egc *egc,
                                        libxl__stream_write_state *stream);
 
@@ -213,7 +210,7 @@ void libxl__stream_write_init(libxl__stream_write_state *stream)
 
     stream->rc = 0;
     stream->running = false;
-    stream->in_checkpoint = false;
+    stream->phase = SWS_PHASE_NORMAL;
     stream->sync_teardown = false;
     FILLZERO(stream->dc);
     stream->record_done_callback = NULL;
@@ -294,9 +291,9 @@ void libxl__stream_write_start_checkpoint(libxl__egc *egc,
                                           libxl__stream_write_state *stream)
 {
     assert(stream->running);
-    assert(!stream->in_checkpoint);
+    assert(stream->phase == SWS_PHASE_NORMAL);
     assert(!stream->back_channel);
-    stream->in_checkpoint = true;
+    stream->phase = SWS_PHASE_CHECKPOINT;
 
     write_emulator_xenstore_record(egc, stream);
 }
@@ -431,12 +428,8 @@ static void emulator_xenstore_record_done(libxl__egc *egc,
 
     if (dss->type == LIBXL_DOMAIN_TYPE_HVM)
         write_emulator_context_record(egc, stream);
-    else {
-        if (stream->in_checkpoint)
-            write_checkpoint_end_record(egc, stream);
-        else
-            write_end_record(egc, stream);
-    }
+    else
+        write_phase_end_record(egc, stream);
 }
 
 static void write_emulator_context_record(libxl__egc *egc,
@@ -534,34 +527,35 @@ static void emulator_context_record_done(libxl__egc *egc,
     free(stream->emu_body);
     stream->emu_body = NULL;
 
-    if (stream->in_checkpoint)
-        write_checkpoint_end_record(egc, stream);
-    else
-        write_end_record(egc, stream);
+    write_phase_end_record(egc, stream);
 }
 
-static void write_end_record(libxl__egc *egc,
-                             libxl__stream_write_state *stream)
+static void write_phase_end_record(libxl__egc *egc,
+                                   libxl__stream_write_state *stream)
 {
     struct libxl__sr_rec_hdr rec;
+    sws_record_done_cb cb;
+    const char *what;
 
     FILLZERO(rec);
-    rec.type = REC_TYPE_END;
-
-    setup_write(egc, stream, "end record",
-                &rec, NULL, stream_success);
-}
-
-static void write_checkpoint_end_record(libxl__egc *egc,
-                                        libxl__stream_write_state *stream)
-{
-    struct libxl__sr_rec_hdr rec;
 
-    FILLZERO(rec);
-    rec.type = REC_TYPE_CHECKPOINT_END;
+    switch (stream->phase) {
+    case SWS_PHASE_NORMAL:
+        rec.type = REC_TYPE_END;
+        what     = "end record";
+        cb       = stream_success;
+        break;
+    case SWS_PHASE_CHECKPOINT:
+        rec.type = REC_TYPE_CHECKPOINT_END;
+        what     = "checkpoint end record";
+        cb       = checkpoint_end_record_done;
+        break;
+    default:
+        /* SWS_PHASE_CHECKPOINT_STATE has no end record */
+        assert(false);
+    }
 
-    setup_write(egc, stream, "checkpoint end record",
-                &rec, NULL, checkpoint_end_record_done);
+    setup_write(egc, stream, what, &rec, NULL, cb);
 }
 
 static void checkpoint_end_record_done(libxl__egc *egc,
@@ -582,21 +576,20 @@ static void stream_complete(libxl__egc *egc,
 {
     assert(stream->running);
 
-    if (stream->in_checkpoint) {
+    switch (stream->phase) {
+    case SWS_PHASE_NORMAL:
+        stream_done(egc, stream, rc);
+        break;
+    case SWS_PHASE_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_save_done()
          */
         checkpoint_done(egc, stream, rc);
-        return;
-    }
-
-    if (stream->in_checkpoint_state) {
-        assert(rc);
-
+        break;
+    case SWS_PHASE_CHECKPOINT_STATE:
         /*
          * If an error is encountered while in a checkpoint, pass it
          * back to libxc.  The failure will come back around to us via
@@ -606,17 +599,15 @@ static void stream_complete(libxl__egc *egc,
          *    libxl__stream_write_abort()
          */
         checkpoint_state_done(egc, stream, rc);
-        return;
+        break;
     }
-
-    stream_done(egc, stream, rc);
 }
 
 static void stream_done(libxl__egc *egc,
                         libxl__stream_write_state *stream, int rc)
 {
     assert(stream->running);
-    assert(!stream->in_checkpoint_state);
+    assert(stream->phase != SWS_PHASE_CHECKPOINT_STATE);
     stream->running = false;
 
     if (stream->emu_carefd)
@@ -640,9 +631,9 @@ static void checkpoint_done(libxl__egc *egc,
                             libxl__stream_write_state *stream,
                             int rc)
 {
-    assert(stream->in_checkpoint);
+    assert(stream->phase == SWS_PHASE_CHECKPOINT);
 
-    stream->in_checkpoint = false;
+    stream->phase = SWS_PHASE_NORMAL;
     stream->checkpoint_callback(egc, stream, rc);
 }
 
@@ -699,9 +690,8 @@ void libxl__stream_write_checkpoint_state(libxl__egc *egc,
     struct libxl__sr_rec_hdr rec;
 
     assert(stream->running);
-    assert(!stream->in_checkpoint);
-    assert(!stream->in_checkpoint_state);
-    stream->in_checkpoint_state = true;
+    assert(stream->phase == SWS_PHASE_NORMAL);
+    stream->phase = SWS_PHASE_CHECKPOINT_STATE;
 
     FILLZERO(rec);
     rec.type = REC_TYPE_CHECKPOINT_STATE;
@@ -720,8 +710,8 @@ static void write_checkpoint_state_done(libxl__egc *egc,
 static void checkpoint_state_done(libxl__egc *egc,
                                   libxl__stream_write_state *stream, int rc)
 {
-    assert(stream->in_checkpoint_state);
-    stream->in_checkpoint_state = false;
+    assert(stream->phase == SWS_PHASE_CHECKPOINT_STATE);
+    stream->phase = SWS_PHASE_NORMAL;
     stream->checkpoint_callback(egc, stream, rc);
 }
 
-- 
2.7.4


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