[PATCH v13 3/8] qapi: add local migration parameter

[Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>]

We are going to implement local-migration feature: some devices will be
able to transfer open file descriptors through migration stream (which
must UNIX domain socket for that purpose).  This allows to transfer the
whole backend state without reconnecting and restarting the backend
service. For example, virtio-net will migrate its attached TAP netdev,
together with its connected file descriptors.

In this commit we introduce a migration parameter, which enables
the feature for devices that support it (none at the moment).

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
---
 include/migration/misc.h |  2 ++
 migration/options.c      | 18 +++++++++++++++++-
 qapi/migration.json      | 12 ++++++++++--
 3 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/include/migration/misc.h b/include/migration/misc.h
index 3159a5e53c3..b14dc70ea3d 100644
--- a/include/migration/misc.h
+++ b/include/migration/misc.h
@@ -156,4 +156,6 @@ bool multifd_device_state_save_thread_should_exit(void);
 void multifd_abort_device_state_save_threads(void);
 bool multifd_join_device_state_save_threads(void);
 
+bool migrate_local(void);
+
 #endif
diff --git a/migration/options.c b/migration/options.c
index f33b2979290..d0d73169354 100644
--- a/migration/options.c
+++ b/migration/options.c
@@ -13,6 +13,7 @@
 
 #include "qemu/osdep.h"
 #include "qemu/error-report.h"
+#include "qapi/util.h"
 #include "exec/target_page.h"
 #include "qapi/clone-visitor.h"
 #include "qapi/error.h"
@@ -24,6 +25,7 @@
 #include "migration/colo.h"
 #include "migration/cpr.h"
 #include "migration/misc.h"
+#include "migration/options.h"
 #include "migration.h"
 #include "migration-stats.h"
 #include "qemu-file.h"
@@ -336,6 +338,12 @@ bool migrate_mapped_ram(void)
     return s->capabilities[MIGRATION_CAPABILITY_MAPPED_RAM];
 }
 
+bool migrate_local(void)
+{
+    MigrationState *s = migrate_get_current();
+    return s->parameters.local;
+}
+
 bool migrate_ignore_shared(void)
 {
     MigrationState *s = migrate_get_current();
@@ -1055,7 +1063,7 @@ static void migrate_mark_all_params_present(MigrationParameters *p)
         &p->has_announce_step, &p->has_block_bitmap_mapping,
         &p->has_x_vcpu_dirty_limit_period, &p->has_vcpu_dirty_limit,
         &p->has_mode, &p->has_zero_page_detection, &p->has_direct_io,
-        &p->has_cpr_exec_command,
+        &p->has_cpr_exec_command, &p->has_local,
     };
 
     len = ARRAY_SIZE(has_fields);
@@ -1394,6 +1402,10 @@ static void migrate_params_test_apply(MigrationParameters *params,
     if (params->has_cpr_exec_command) {
         dest->cpr_exec_command = params->cpr_exec_command;
     }
+
+    if (params->has_local) {
+        dest->local = params->local;
+    }
 }
 
 static void migrate_params_apply(MigrationParameters *params)
@@ -1522,6 +1534,10 @@ static void migrate_params_apply(MigrationParameters *params)
         s->parameters.cpr_exec_command =
             QAPI_CLONE(strList, params->cpr_exec_command);
     }
+
+    if (params->has_local) {
+        s->parameters.local = params->local;
+    }
 }
 
 void qmp_migrate_set_parameters(MigrationParameters *params, Error **errp)
diff --git a/qapi/migration.json b/qapi/migration.json
index 7134d4ce47e..cf7037ed3fc 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -831,7 +831,8 @@
            'mode',
            'zero-page-detection',
            'direct-io',
-           'cpr-exec-command'] }
+           'cpr-exec-command',
+           'local'] }
 
 ##
 # @migrate-set-parameters:
@@ -1007,6 +1008,12 @@
 #     is @cpr-exec.  The first list element is the program's filename,
 #     the remainder its arguments.  (Since 10.2)
 #
+# @local: Enable local migration for devices that support it.  Backend
+#     state and its file descriptors can then be passed to the
+#     destination in the migration channel.  The migration channel
+#     must be a Unix domain socket.  Usually needs to be enabled per
+#     device.  (Since 11.0)
+#
 # Features:
 #
 # @unstable: Members @x-checkpoint-delay and
@@ -1046,7 +1053,8 @@
             '*mode': 'MigMode',
             '*zero-page-detection': 'ZeroPageDetection',
             '*direct-io': 'bool',
-            '*cpr-exec-command': [ 'str' ]} }
+            '*cpr-exec-command': [ 'str' ],
+            '*local': 'bool' } }
 
 ##
 # @query-migrate-parameters:
-- 
2.52.0