[dm-devel] Resizing multipath maps: reload ioctl failed: Invalid argument

[Tore Anderson]

   Hello,

* Jun'ichi Nomura

> It's due to kernel device-mapper restriction.
> 
> multipath-tools uses no_flush suspend of device-mapper device to save
> I/O errors in all-paths-down case. (Without the option, device-mapper
> needs to flush all pending I/Os, that will result in I/O errors if
> there is no working path.)
> 
> For no_flush suspend, resizing is disabled because of known
> dead-lock: it requires a lock that can be kept hold until the pending
> I/Os are flushed.

   Hmm.  So this deadlock is a kernel bug that (hopefully) will be fixed
  in the future, so resizing can again be enabled, or is this a design
  limitation that it's impossible to do something about?

   Can the no_flush thing be toggled online;  that is, would it be
  possible to alter multipath-tools so that when it attempted to resize a
  map, it would disable no_flush, resize it, and then re-enable it?  I
  think a two-second window of vulnerability to all-paths-down is
  acceptable...

   Similarily, if this no_flush option is relevant only when
  features=queue_if_no_paths (at least that's the impression I get from
  your description of it), would it work to temporarily reload the map
  without this feature, resize the volume, than re-add queue_if_no_path?

> A workaround for it would be using modified multipath-tools which
> doesn't use no_noflush.

   I grepped for noflush and no_flush (and so on) in the multipath-tools
  source code but can't really find where it is set..?

Thanks
-- 
Tore Anderson