[openib-general] Re: RFD: uverbs and hotplug

[Michael S. Tsirkin]

Quoting r. Roland Dreier <roland at topspin.com>:
> Subject: Re: RFD: uverbs and hotplug
> 
>     Michael> Hello, Roland, all!  How should hotplug work with uverbs?
> 
> It's complicated.  Discussion now is useful but I would definitely
> prefer to hold off on any implementation until we have the basic
> userspace verbs support merged upstream.

I agree.

> One possibility is that it is the administrator's responsibility to
> close down all applications using the device before hot-removing it.

Killing applications probably does not cut it - its the applications
that are important, not networking.
The administrator also may have no idea what these applications are.

> Another possibility is as you described: free all the resources
> allocated by userspace processes (including remapping any doorbell
> pages) before allowing the hot-remove to proceed.  In this case, one
> could generate an asynchronous event to tell applications that their
> HCA is now gone.

Okay, but you still must blocks the applications from accessing the
hardware - you cant trust them not to.

> Do you know what happens today if one has a filesystem mounted and then
> hot-remove the HBA that is used to get to the underlying block device?
> 
>  - R.

No, but I know how NIC hotplug works on my laptop: push
a button, wait till a little light flashes, pull it out.

-- 
MST - Michael S. Tsirkin