[Qemu-devel] [PATCH v7 22/42] migrate_start_postcopy: Command to trigger transition to postcopy

[Dr. David Alan Gilbert (git)]

From: "Dr. David Alan Gilbert" <address@hidden>

Once postcopy is enabled (with migrate_set_capability), the migration
will still start on precopy mode.  To cause a transition into postcopy
the:

  migrate_start_postcopy

command must be issued.  Postcopy will start sometime after this
(when it's next checked in the migration loop).

Issuing the command before migration has started will error,
and issuing after it has finished is ignored.

Signed-off-by: Dr. David Alan Gilbert <address@hidden>
Reviewed-by: Eric Blake <address@hidden>
---
 hmp-commands.hx               | 15 +++++++++++++++
 hmp.c                         |  7 +++++++
 hmp.h                         |  1 +
 include/migration/migration.h |  3 +++
 migration/migration.c         | 22 ++++++++++++++++++++++
 qapi-schema.json              |  8 ++++++++
 qmp-commands.hx               | 19 +++++++++++++++++++
 7 files changed, 75 insertions(+)

diff --git a/hmp-commands.hx b/hmp-commands.hx
index 3d7dfcc..5124698 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -1006,6 +1006,21 @@ Set the parameter @var{parameter} for migration.
 ETEXI
 
     {
+        .name       = "migrate_start_postcopy",
+        .args_type  = "",
+        .params     = "",
+        .help       = "Switch migration to postcopy mode",
+        .mhandler.cmd = hmp_migrate_start_postcopy,
+    },
+
+STEXI
address@hidden migrate_start_postcopy
address@hidden migrate_start_postcopy
+Switch in-progress migration to postcopy mode. Ignored after the end of
+migration (or once already in postcopy).
+ETEXI
+
+    {
         .name       = "client_migrate_info",
         .args_type  = 
"protocol:s,hostname:s,port:i?,tls-port:i?,cert-subject:s?",
         .params     = "protocol hostname port tls-port cert-subject",
diff --git a/hmp.c b/hmp.c
index 514f22f..bf1ad53 100644
--- a/hmp.c
+++ b/hmp.c
@@ -1268,6 +1268,13 @@ void hmp_client_migrate_info(Monitor *mon, const QDict 
*qdict)
     hmp_handle_error(mon, &err);
 }
 
+void hmp_migrate_start_postcopy(Monitor *mon, const QDict *qdict)
+{
+    Error *err = NULL;
+    qmp_migrate_start_postcopy(&err);
+    hmp_handle_error(mon, &err);
+}
+
 void hmp_set_password(Monitor *mon, const QDict *qdict)
 {
     const char *protocol  = qdict_get_str(qdict, "protocol");
diff --git a/hmp.h b/hmp.h
index a70ac4f..97901c2 100644
--- a/hmp.h
+++ b/hmp.h
@@ -68,6 +68,7 @@ void hmp_migrate_set_capability(Monitor *mon, const QDict 
*qdict);
 void hmp_migrate_set_parameter(Monitor *mon, const QDict *qdict);
 void hmp_migrate_set_cache_size(Monitor *mon, const QDict *qdict);
 void hmp_client_migrate_info(Monitor *mon, const QDict *qdict);
+void hmp_migrate_start_postcopy(Monitor *mon, const QDict *qdict);
 void hmp_set_password(Monitor *mon, const QDict *qdict);
 void hmp_expire_password(Monitor *mon, const QDict *qdict);
 void hmp_eject(Monitor *mon, const QDict *qdict);
diff --git a/include/migration/migration.h b/include/migration/migration.h
index a5951ac..e973490 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -111,6 +111,9 @@ struct MigrationState
     int64_t xbzrle_cache_size;
     int64_t setup_time;
     int64_t dirty_sync_count;
+
+    /* Flag set once the migration has been asked to enter postcopy */
+    bool start_postcopy;
 };
 
 void process_incoming_migration(QEMUFile *f);
diff --git a/migration/migration.c b/migration/migration.c
index e77b8b4..6fc47f9 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -465,6 +465,28 @@ void qmp_migrate_set_parameters(bool has_compress_level,
     }
 }
 
+void qmp_migrate_start_postcopy(Error **errp)
+{
+    MigrationState *s = migrate_get_current();
+
+    if (!migrate_postcopy_ram()) {
+        error_setg(errp, "Enable postcopy with migration_set_capability before"
+                         " the start of migration");
+        return;
+    }
+
+    if (s->state == MIGRATION_STATUS_NONE) {
+        error_setg(errp, "Postcopy must be started after migration has been"
+                         " started");
+        return;
+    }
+    /*
+     * we don't error if migration has finished since that would be racy
+     * with issuing this command.
+     */
+    atomic_set(&s->start_postcopy, true);
+}
+
 /* shared migration helpers */
 
 static void migrate_set_state(MigrationState *s, int old_state, int new_state)
diff --git a/qapi-schema.json b/qapi-schema.json
index 0b6fe54..b0177bb 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -661,6 +661,14 @@
             '*tls-port': 'int', '*cert-subject': 'str' } }
 
 ##
+# @migrate-start-postcopy
+#
+# Switch migration to postcopy mode
+#
+# Since: 2.4
+{ 'command': 'migrate-start-postcopy' }
+
+##
 # @MouseInfo:
 #
 # Information about a mouse device.
diff --git a/qmp-commands.hx b/qmp-commands.hx
index 867a21f..dc63ff3 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -713,6 +713,25 @@ Example:
 
 EQMP
     {
+        .name       = "migrate-start-postcopy",
+        .args_type  = "",
+        .mhandler.cmd_new = qmp_marshal_input_migrate_start_postcopy,
+    },
+
+SQMP
+migrate-start-postcopy
+----------------------
+
+Switch an in-progress migration to postcopy mode. Ignored after the end of
+migration (or once already in postcopy).
+
+Example:
+-> { "execute": "migrate-start-postcopy" }
+<- { "return": {} }
+
+EQMP
+
+    {
         .name       = "query-migrate-cache-size",
         .args_type  = "",
         .mhandler.cmd_new = qmp_marshal_input_query_migrate_cache_size,
-- 
2.4.3