[PATCH v0 2/4] migration: add background snapshot capability

[Denis Plotnikov <dplotnikov@virtuozzo.com>]

The capability is used for background snapshot enabling.
The background snapshot logic is going to be added in the following
patch.

Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
---
 qapi/migration.json   |  7 ++++++-
 migration/migration.h |  1 +
 migration/migration.c | 35 +++++++++++++++++++++++++++++++++++
 3 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/qapi/migration.json b/qapi/migration.json
index d5000558c6..46681a5c3c 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -424,6 +424,11 @@
 # @validate-uuid: Send the UUID of the source to allow the destination
 #                 to ensure it is the same. (since 4.2)
 #
+# @background-snapshot: If enabled, the migration stream will be a snapshot
+#                       of the VM exactly at the point when the migration
+#                       procedure starts. The VM RAM is saved with running VM.
+#                       (since 5.2)
+#
 # Since: 1.2
 ##
 { 'enum': 'MigrationCapability',
@@ -431,7 +436,7 @@
            'compress', 'events', 'postcopy-ram', 'x-colo', 'release-ram',
            'block', 'return-path', 'pause-before-switchover', 'multifd',
            'dirty-bitmaps', 'postcopy-blocktime', 'late-block-activate',
-           'x-ignore-shared', 'validate-uuid' ] }
+           'x-ignore-shared', 'validate-uuid', 'background-snapshot' ] }
 
 ##
 # @MigrationCapabilityStatus:
diff --git a/migration/migration.h b/migration/migration.h
index f617960522..63f2fde9a3 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -322,6 +322,7 @@ int migrate_compress_wait_thread(void);
 int migrate_decompress_threads(void);
 bool migrate_use_events(void);
 bool migrate_postcopy_blocktime(void);
+bool migrate_background_snapshot(void);
 
 /* Sending on the return path - generic and then for each message type */
 void migrate_send_rp_shut(MigrationIncomingState *mis,
diff --git a/migration/migration.c b/migration/migration.c
index 2ed9923227..2ec0451abe 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -1086,6 +1086,32 @@ static bool migrate_caps_check(bool *cap_list,
             error_setg(errp, "Postcopy is not compatible with ignore-shared");
             return false;
         }
+
+        if (cap_list[MIGRATION_CAPABILITY_BACKGROUND_SNAPSHOT]) {
+            error_setg(errp, "Postcopy is not compatible "
+                        "with background snapshot");
+            return false;
+        }
+    }
+
+    if (cap_list[MIGRATION_CAPABILITY_BACKGROUND_SNAPSHOT]) {
+        if (cap_list[MIGRATION_CAPABILITY_RELEASE_RAM]) {
+            error_setg(errp, "Background snapshot is not compatible "
+                        "with release ram capability");
+            return false;
+        }
+
+        if (cap_list[MIGRATION_CAPABILITY_COMPRESS]) {
+            error_setg(errp, "Background snapshot is not "
+                        "currently compatible with compression");
+            return false;
+        }
+
+        if (cap_list[MIGRATION_CAPABILITY_XBZRLE]) {
+            error_setg(errp, "Background snapshot is not "
+                        "currently compatible with XBZLRE");
+            return false;
+        }
     }
 
     return true;
@@ -2390,6 +2416,15 @@ bool migrate_use_block_incremental(void)
     return s->parameters.block_incremental;
 }
 
+bool migrate_background_snapshot(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->enabled_capabilities[MIGRATION_CAPABILITY_BACKGROUND_SNAPSHOT];
+}
+
 /* migration thread support */
 /*
  * Something bad happened to the RP stream, mark an error
-- 
2.17.0