migrate: Introduce a 'dc->vmsd' check to avoid segfault for --only-migratable

Commit a3a3d8c7 introduced a segfault bug while checking for
'dc->vmsd->unmigratable' which caused QEMU to crash when trying to add
devices which do no set their 'dc->vmsd' yet while initialization.
Place a 'dc->vmsd' check prior to it so that we do not segfault for
such devices.

NOTE: This doesn't compromise the functioning of --only-migratable
option as all the unmigratable devices do set their 'dc->vmsd'.

Introduce a new function check_migratable() and move the
only_migratable check inside it, also use stubs to avoid user-mode qemu
build failures.

Signed-off-by: Ashijeet Acharya <ashijeetacharya@gmail.com>
Message-Id: <1487009088-23891-1-git-send-email-ashijeetacharya@gmail.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/migration/migration.c b/migration/migration.c
index 4fab538fe0..481c540a6d 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -1150,6 +1150,21 @@ void migrate_del_blocker(Error *reason)
     migration_blockers = g_slist_remove(migration_blockers, reason);
 }
 
+int check_migratable(Object *obj, Error **err)
+{
+    DeviceClass *dc = DEVICE_GET_CLASS(obj);
+    if (only_migratable && dc->vmsd) {
+        if (dc->vmsd->unmigratable) {
+            error_setg(err, "Device %s is not migratable, but "
+                       "--only-migratable was specified",
+                       object_get_typename(obj));
+            return -1;
+        }
+    }
+
+    return 0;
+}
+
 void qmp_migrate_incoming(const char *uri, Error **errp)
 {
     Error *local_err = NULL;