[PATCH 4/7] migration: Split migration_channel_process_incoming()

[Peter Xu <peterx@redhat.com>]

Introduce two smaller functions for it,

- migration_incoming_channel_install(): peek at channels whenever possible,
  and install the channel to one of the slots (main, multifd, preempt)

- migration_incoming_error_propagate(): handling an error happened during
  channel establish phase of an incoming migration.

When at it, move the set channel tracepoint into the 1st helper, replacing
the existing tracepoint with trace_migration_channel_process_incoming().
So far, they should fire almost the same time if the channel peek worked.
This fact will change in follow up refactorings.

I also moved migration_ioc_register_yank() to be after identify, hopefully
it makes more sense: we'd better be careful on registration of yank, or we
should be prepared for explosions.  Previously it worked, my guess is when
error happens we never unregister yank but hang dest QEMU or quit,
depending on exit_on_error value.

No real functional change intended.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 migration/channel.c    | 57 +++++++++++++++++++++++++++++-------------
 migration/trace-events |  1 +
 2 files changed, 41 insertions(+), 17 deletions(-)

diff --git a/migration/channel.c b/migration/channel.c
index 266ae8f776..8407ea46cb 100644
--- a/migration/channel.c
+++ b/migration/channel.c
@@ -197,6 +197,42 @@ out:
     return channel;
 }
 
+static void migration_incoming_error_propagate(MigrationIncomingState *mis,
+                                               Error *error)
+{
+    error_report_err(error);
+    migrate_set_state(&mis->state, mis->state, MIGRATION_STATUS_FAILED);
+    if (mis->exit_on_error) {
+        exit(EXIT_FAILURE);
+    }
+}
+
+static bool migration_incoming_channel_install(MigrationIncomingState *mis,
+                                               QIOChannel *ioc,
+                                               Error **errp)
+{
+    MigChannelType ch = migration_channel_identify(mis, ioc, errp);
+
+    if (!ch) {
+        assert(*errp);
+        return false;
+    }
+
+    trace_migration_set_incoming_channel(ioc,
+                                         object_get_typename(OBJECT(ioc)));
+    migration_ioc_register_yank(ioc);
+
+    if (migration_incoming_setup(ioc, ch, errp)) {
+        migration_start_incoming();
+    }
+
+    if (*errp) {
+        return false;
+    }
+
+    return true;
+}
+
 /**
  * @migration_channel_process_incoming - Create new incoming migration channel
  *
@@ -209,31 +245,18 @@ void migration_channel_process_incoming(QIOChannel *ioc)
 {
     MigrationIncomingState *mis = migration_incoming_get_current();
     Error *local_err = NULL;
-    MigChannelType ch;
 
-    trace_migration_set_incoming_channel(
+    trace_migration_channel_process_incoming(
         ioc, object_get_typename(OBJECT(ioc)));
 
     if (migrate_channel_requires_tls_upgrade(ioc)) {
         migration_tls_channel_process_incoming(ioc, &local_err);
     } else {
-        migration_ioc_register_yank(ioc);
-        ch = migration_channel_identify(mis, ioc, &local_err);
-        if (!ch) {
-            goto out;
-        }
-
-        if (migration_incoming_setup(ioc, ch, &local_err)) {
-            migration_start_incoming();
-        }
+        migration_incoming_channel_install(mis, ioc, &local_err);
     }
-out:
+
     if (local_err) {
-        error_report_err(local_err);
-        migrate_set_state(&mis->state, mis->state, MIGRATION_STATUS_FAILED);
-        if (mis->exit_on_error) {
-            exit(EXIT_FAILURE);
-        }
+        migration_incoming_error_propagate(mis, local_err);
     }
 }
 
diff --git a/migration/trace-events b/migration/trace-events
index e755872496..c5fa88fe8f 100644
--- a/migration/trace-events
+++ b/migration/trace-events
@@ -207,6 +207,7 @@ migration_start_incoming(void) ""
 migration_transferred_bytes(uint64_t qemu_file, uint64_t multifd, uint64_t rdma) "qemu_file %" PRIu64 " multifd %" PRIu64 " RDMA %" PRIu64
 
 # channel.c
+migration_channel_process_incoming(void *ioc, const char *ioctype) "ioc=%p ioctype=%s"
 migration_set_incoming_channel(void *ioc, const char *ioctype) "ioc=%p ioctype=%s"
 migration_set_outgoing_channel(void *ioc, const char *ioctype) "ioc=%p ioctype=%s"
 
-- 
2.55.0