migration: Add zero-copy-send parameter for QMP/HMP for Linux

Add property that allows zero-copy migration of memory pages
on the sending side, and also includes a helper function
migrate_use_zero_copy_send() to check if it's enabled.

No code is introduced to actually do the migration, but it allow
future implementations to enable/disable this feature.

On non-Linux builds this parameter is compiled-out.

Signed-off-by: Leonardo Bras <leobras@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20220513062836.965425-5-leobras@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

3 files changed, 46 insertions, 2 deletions

diff --git a/migration/migration.c b/migration/migration.c
index 5a31b23bd6..3e91f4b5e2 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -910,6 +910,10 @@ MigrationParameters *qmp_query_migrate_parameters(Error **errp)
     params->multifd_zlib_level = s->parameters.multifd_zlib_level;
     params->has_multifd_zstd_level = true;
     params->multifd_zstd_level = s->parameters.multifd_zstd_level;
+#ifdef CONFIG_LINUX
+    params->has_zero_copy_send = true;
+    params->zero_copy_send = s->parameters.zero_copy_send;
+#endif
     params->has_xbzrle_cache_size = true;
     params->xbzrle_cache_size = s->parameters.xbzrle_cache_size;
     params->has_max_postcopy_bandwidth = true;
@@ -1567,6 +1571,11 @@ static void migrate_params_test_apply(MigrateSetParameters *params,
     if (params->has_multifd_compression) {
         dest->multifd_compression = params->multifd_compression;
     }
+#ifdef CONFIG_LINUX
+    if (params->has_zero_copy_send) {
+        dest->zero_copy_send = params->zero_copy_send;
+    }
+#endif
     if (params->has_xbzrle_cache_size) {
         dest->xbzrle_cache_size = params->xbzrle_cache_size;
     }
@@ -1679,6 +1688,11 @@ static void migrate_params_apply(MigrateSetParameters *params, Error **errp)
     if (params->has_multifd_compression) {
         s->parameters.multifd_compression = params->multifd_compression;
     }
+#ifdef CONFIG_LINUX
+    if (params->has_zero_copy_send) {
+        s->parameters.zero_copy_send = params->zero_copy_send;
+    }
+#endif
     if (params->has_xbzrle_cache_size) {
         s->parameters.xbzrle_cache_size = params->xbzrle_cache_size;
         xbzrle_cache_resize(params->xbzrle_cache_size, errp);
@@ -2563,6 +2577,17 @@ int migrate_multifd_zstd_level(void)
     return s->parameters.multifd_zstd_level;
 }
 
+#ifdef CONFIG_LINUX
+bool migrate_use_zero_copy_send(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->parameters.zero_copy_send;
+}
+#endif
+
 int migrate_use_xbzrle(void)
 {
     MigrationState *s;
@@ -4206,6 +4231,10 @@ static Property migration_properties[] = {
     DEFINE_PROP_UINT8("multifd-zstd-level", MigrationState,
                       parameters.multifd_zstd_level,
                       DEFAULT_MIGRATE_MULTIFD_ZSTD_LEVEL),
+#ifdef CONFIG_LINUX
+    DEFINE_PROP_BOOL("zero_copy_send", MigrationState,
+                      parameters.zero_copy_send, false),
+#endif
     DEFINE_PROP_SIZE("xbzrle-cache-size", MigrationState,
                       parameters.xbzrle_cache_size,
                       DEFAULT_MIGRATE_XBZRLE_CACHE_SIZE),
@@ -4303,6 +4332,9 @@ static void migration_instance_init(Object *obj)
     params->has_multifd_compression = true;
     params->has_multifd_zlib_level = true;
     params->has_multifd_zstd_level = true;
+#ifdef CONFIG_LINUX
+    params->has_zero_copy_send = true;
+#endif
     params->has_xbzrle_cache_size = true;
     params->has_max_postcopy_bandwidth = true;
     params->has_max_cpu_throttle = true;
diff --git a/migration/migration.h b/migration/migration.h
index a863032b71..e8f2941a55 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -375,6 +375,11 @@ MultiFDCompression migrate_multifd_compression(void);
 int migrate_multifd_zlib_level(void);
 int migrate_multifd_zstd_level(void);
 
+#ifdef CONFIG_LINUX
+bool migrate_use_zero_copy_send(void);
+#else
+#define migrate_use_zero_copy_send() (false)
+#endif
 int migrate_use_xbzrle(void);
 uint64_t migrate_xbzrle_cache_size(void);
 bool migrate_colo_enabled(void);
diff --git a/migration/socket.c b/migration/socket.c
index 05705a32d8..3754d8f72c 100644
--- a/migration/socket.c
+++ b/migration/socket.c
@@ -74,9 +74,16 @@ static void socket_outgoing_migration(QIOTask *task,
 
     if (qio_task_propagate_error(task, &err)) {
         trace_migration_socket_outgoing_error(error_get_pretty(err));
-    } else {
-        trace_migration_socket_outgoing_connected(data->hostname);
+           goto out;
     }
+
+    trace_migration_socket_outgoing_connected(data->hostname);
+
+    if (migrate_use_zero_copy_send()) {
+        error_setg(&err, "Zero copy send not available in migration");
+    }
+
+out:
     migration_channel_connect(data->s, sioc, data->hostname, err);
     object_unref(OBJECT(sioc));
 }