[PATCH] migration: Provide a test for migratability

[Dr. David Alan Gilbert (git)]

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

Provide a simple way to see if there's currently a migration blocker in
operation:

$ ./x86_64-softmmu/qemu-system-x86_64 -nographic -M pc,usb=on -chardev 
null,id=n -device usb-serial,chardev=n

(qemu) info migratable
Error: State blocked by non-migratable device '0000:00:01.2/1/usb-serial'

$ ./x86_64-softmmu/qemu-system-x86_64 -nographic

(qemu) info migratable
Migratable

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 hmp-commands-info.hx  | 14 ++++++++++++++
 include/monitor/hmp.h |  1 +
 migration/migration.c |  5 +++++
 monitor/hmp-cmds.c    | 13 +++++++++++++
 qapi/migration.json   | 14 ++++++++++++++
 5 files changed, 47 insertions(+)

diff --git a/hmp-commands-info.hx b/hmp-commands-info.hx
index 117ba25f91..c2d7ac2f11 100644
--- a/hmp-commands-info.hx
+++ b/hmp-commands-info.hx
@@ -541,6 +541,20 @@ SRST
     Show migration status.
 ERST
 
+    {
+        .name       = "migratable",
+        .args_type  = "",
+        .params     = "",
+        .help       = "tests if VM is migratable",
+        .cmd        = hmp_info_migratable,
+    },
+
+SRST
+  ''info migratable''
+    Tests whether the VM is currently migratable.
+ERST
+
+
     {
         .name       = "migrate_capabilities",
         .args_type  = "",
diff --git a/include/monitor/hmp.h b/include/monitor/hmp.h
index ed2913fd18..0dd7941daf 100644
--- a/include/monitor/hmp.h
+++ b/include/monitor/hmp.h
@@ -25,6 +25,7 @@ void hmp_info_status(Monitor *mon, const QDict *qdict);
 void hmp_info_uuid(Monitor *mon, const QDict *qdict);
 void hmp_info_chardev(Monitor *mon, const QDict *qdict);
 void hmp_info_mice(Monitor *mon, const QDict *qdict);
+void hmp_info_migratable(Monitor *mon, const QDict *qdict);
 void hmp_info_migrate(Monitor *mon, const QDict *qdict);
 void hmp_info_migrate_capabilities(Monitor *mon, const QDict *qdict);
 void hmp_info_migrate_parameters(Monitor *mon, const QDict *qdict);
diff --git a/migration/migration.c b/migration/migration.c
index 5e330cc6eb..8745a5b9f9 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -2234,6 +2234,11 @@ int64_t qmp_query_migrate_cache_size(Error **errp)
     return migrate_xbzrle_cache_size();
 }
 
+void qmp_query_migratable(Error **errp)
+{
+    migration_is_blocked(errp);
+}
+
 void qmp_migrate_set_speed(int64_t value, Error **errp)
 {
     MigrateSetParameters p = {
diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
index ef569035f8..a7f48b3512 100644
--- a/monitor/hmp-cmds.c
+++ b/monitor/hmp-cmds.c
@@ -216,6 +216,19 @@ static char *SocketAddress_to_str(SocketAddress *addr)
     }
 }
 
+void hmp_info_migratable(Monitor *mon, const QDict *qdict)
+{
+    Error *err = NULL;
+    /* It's migratable if this succeeds */
+    qmp_query_migratable(&err);
+    if (err) {
+        hmp_handle_error(mon, err);
+        return;
+    }
+
+    monitor_printf(mon, "Migratable\n");
+}
+
 void hmp_info_migrate(Monitor *mon, const QDict *qdict)
 {
     MigrationInfo *info;
diff --git a/qapi/migration.json b/qapi/migration.json
index d1d9632c2a..07aee9907c 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -366,6 +366,20 @@
 ##
 { 'command': 'query-migrate', 'returns': 'MigrationInfo' }
 
+##
+# @query-migratable:
+# Tests whether it will be possible to migrate the VM in the current state.
+#
+# Returns: nothing on success (i.e. if the VM is migratable)
+#
+# Since: 6.0
+# Example:
+#
+# -> { "execute": "query-migratable" }
+# <- { "return": {} }
+##
+{ 'command': 'query-migratable' }
+
 ##
 # @MigrationCapability:
 #
-- 
2.29.2