[Qemu-devel] [PATCH 3/8] migration: add new capability test-only

["Denis V. Lunev" <den@openvz.org>]

From: Igor Redko <redkoi@virtuozzo.com>

This patch declares a new migration capability that allows
to distinguish between true migration and the test.

An alternative is using a custom URI but in this case the
following problems should be solved:
1/ QEMUFile abstraction hides the real transport type
2/ We must be ensured that VM will not be stopped due to
“successful migration”

Possible solutions:
1/ Using global variable analogous to
s->enabled_capabilities[MIGRATION_CAPABILITY_TEST_ONLY] that
will be initialized according to the migration type at the
beginning of the migration process
2/ Additional hook, presence of implementation of which allows
to decide whether the migration is true

Signed-off-by: Igor Redko <redkoi@virtuozzo.com>
Reviewed-by: Anna Melekhova <annam@virtuozzo.com>
Signed-off-by: Denis V. Lunev <den@openvz.org>
---
 include/migration/migration.h | 2 ++
 migration/migration.c         | 9 +++++++++
 qapi-schema.json              | 5 ++++-
 qmp-commands.hx               | 1 +
 4 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/include/migration/migration.h b/include/migration/migration.h
index deb0d21..8611750 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -179,6 +179,8 @@ int migrate_compress_threads(void);
 int migrate_decompress_threads(void);
 bool migrate_use_events(void);
 
+bool migrate_is_test(void);
+
 void ram_control_before_iterate(QEMUFile *f, uint64_t flags);
 void ram_control_after_iterate(QEMUFile *f, uint64_t flags);
 void ram_control_load_hook(QEMUFile *f, uint64_t flags, void *data);
diff --git a/migration/migration.c b/migration/migration.c
index b710a2d..e0cad54 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -954,6 +954,15 @@ int migrate_use_xbzrle(void)
     return s->enabled_capabilities[MIGRATION_CAPABILITY_XBZRLE];
 }
 
+bool migrate_is_test(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->enabled_capabilities[MIGRATION_CAPABILITY_TEST_ONLY];
+}
+
 int64_t migrate_xbzrle_cache_size(void)
 {
     MigrationState *s;
diff --git a/qapi-schema.json b/qapi-schema.json
index 8b0520c..38bf199 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -540,11 +540,14 @@
 # @auto-converge: If enabled, QEMU will automatically throttle down the guest
 #          to speed up convergence of RAM migration. (since 1.6)
 #
+# @test-only: If enabled, QEMU instead of migrating will estimate migration
+#          time basing on given downtime and current dirty page rate
+#
 # Since: 1.2
 ##
 { 'enum': 'MigrationCapability',
   'data': ['xbzrle', 'rdma-pin-all', 'auto-converge', 'zero-blocks',
-           'compress', 'events'] }
+           'compress', 'events', 'test-only'] }
 
 ##
 # @MigrationCapabilityStatus
diff --git a/qmp-commands.hx b/qmp-commands.hx
index d2ba800..741d088 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -3456,6 +3456,7 @@ Enable/Disable migration capabilities
 - "auto-converge": throttle down guest to help convergence of migration
 - "zero-blocks": compress zero blocks during block migration
 - "events": generate events for each migration state change
+- "test-only": don't send any data, instead estimate dirty page rate
 
 Arguments:
 
-- 
2.1.4