qapi: Add device ID and head parameters to screendump

QEMU's screendump command can only take dumps from the primary display.
When using multiple VGA cards, there is no way to get a dump from a
secondary card or other display heads yet. So let's add a 'device' and
a 'head' parameter to the HMP and QMP commands to be able to specify
alternative devices and heads with the screendump command, too.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 1520267868-31778-1-git-send-email-thuth@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
diff --git a/hmp.c b/hmp.c
index 016cb5c..ba9e299 100644
--- a/hmp.c
+++ b/hmp.c
@@ -2140,9 +2140,11 @@
 void hmp_screendump(Monitor *mon, const QDict *qdict)
 {
     const char *filename = qdict_get_str(qdict, "filename");
+    const char *id = qdict_get_try_str(qdict, "device");
+    int64_t head = qdict_get_try_int(qdict, "head", 0);
     Error *err = NULL;
 
-    qmp_screendump(filename, &err);
+    qmp_screendump(filename, id != NULL, id, id != NULL, head, &err);
     hmp_handle_error(mon, &err);
 }