[openstack-dev] [nova] Do we need a config option for use_usb_tablet/pointer_model?

Matt Riedemann mriedem at linux.vnet.ibm.com
Fri Jun 17 20:36:53 UTC 2016

I was reviewing the last change in this blueprint series today:


And started to question why we even have a config option for this 
anymore. The blueprint didn't have a spec but there are some details in 
the description about the use cases:


 From the code and help text for the option I realize that there is some 
per-compute enablement required for this to work (VNC or SPICE enabled 
and the SPICE agent disabled). But otherwise it seems totally 
image-specific, which is why the blueprint is adding support for 
calculating whether or not to enable USB support in the guest based on 
the image metadata properties.

But do we still need the configuration option then?

The tricky scenario I have in mind is I create my Windows instance on a 
host that has use_usb_table=True and I can use my USB pointer mouse and 
I'm happy, yay! Then that host goes under maintenance, the admin 
migrates it to another host that has use_usb_tablet=False and now I 
can't use my USB mouse anymore. I guess the chance of this happening are 
pretty slim given use_usb_tablet defaults to True.

However, in https://review.openstack.org/#/c/176242/ use_usb_table is 
deprecated in favor of the new 'pointer_model' config option which 
defaults to None, so it's not backward compatible with use_usb_tablet 
and when we remove use_usb_tablet as an option in Ocata, the default 
behavior has changed.

Anyway, my point is, why do we even need a config option for this at all 
if the image metadata can tell us what to do now?



Matt Riedemann

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