[Qemu-devel] [PULL 8/8] Postcopy: Check for support when setting the capability

[Amit Shah]

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

Knowing whether the destination host supports migration with
postcopy can be tricky.
The destination doesn't need the capability set, however
if we set it then use the opportunity to do the test and
tell the user/management layer early.

Signed-off-by: Dr. David Alan Gilbert <address@hidden>
Message-Id: <address@hidden>
Signed-off-by: Amit Shah <address@hidden>
---
 migration/migration.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/migration/migration.c b/migration/migration.c
index 213580d..20f8875 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -720,6 +720,7 @@ void 
qmp_migrate_set_capabilities(MigrationCapabilityStatusList *params,
 {
     MigrationState *s = migrate_get_current();
     MigrationCapabilityStatusList *cap;
+    bool old_postcopy_cap = migrate_postcopy_ram();
 
     if (migration_is_setup_or_active(s->state)) {
         error_setg(errp, QERR_MIGRATION_ACTIVE);
@@ -742,6 +743,19 @@ void 
qmp_migrate_set_capabilities(MigrationCapabilityStatusList *params,
             s->enabled_capabilities[MIGRATION_CAPABILITY_POSTCOPY_RAM] =
                 false;
         }
+        /* This check is reasonably expensive, so only when it's being
+         * set the first time, also it's only the destination that needs
+         * special support.
+         */
+        if (!old_postcopy_cap && runstate_check(RUN_STATE_INMIGRATE) &&
+            !postcopy_ram_supported_by_host()) {
+            /* postcopy_ram_supported_by_host will have emitted a more
+             * detailed message
+             */
+            error_report("Postcopy is not supported");
+            s->enabled_capabilities[MIGRATION_CAPABILITY_POSTCOPY_RAM] =
+                false;
+        }
     }
 }
 
-- 
2.7.4