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Hi,

Currently there is no way to update the volume-attachment bdm parameters,
i.e. the bus type or device name, without detaching and re-attaching the
volume, and supplying the new parameters. This is obviously not ideal, and
if the volume we want to update is the boot volume, detaching to update the
bdm, is not even possible.

I want to send a spec proposition to allow updating those attachment
parameters, while the server is shutoff of course.

A question is what do you think is the right API for this request.
My first thought is to expand the "os-volume_attachments" API and to add a
PUT method which will get new bdm parameters. Problem is the POST method
doesn't get all the parameters in a bdm - only a device_name.

The options I can think off are:
1. Add to the POST and to the PUT "os-volume_attachments" methods, in the
volumeAttachment dict all the parameters from the bdm that we want the user
to be able to update - probably just device_type and bus_type (device_name
is already present). They will be optional of course, for
backward-compatibility.
2. Instead of expanding the "os-volume_attachments" API, expand the other
way to attach a volume - through a server "attach" action request. We can
add another action - "attachUpdate", which will get the same parameters as
the volume-attach, including the bdm parameters, and with that the user can
update the bdm.

What do you think about the proposal and about the API dilemma?

Thanks,
Shoham
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