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Re: [Xen-devel] [PATCH] VM-Tool: C-based Xen management tools

To: Anthony Liguori <aliguori@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] VM-Tool: C-based Xen management tools
From: Mark Williamson <Mark.Williamson@xxxxxxxxxxxx>
Date: Mon, 14 Feb 2005 16:35:48 +0000
Cc: Mark Williamson <Mark.Williamson@xxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxxx, Nivedita Singhvi <niv@xxxxxxxxxx>
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> Yes, PCI wouldn't be too hard to abstract.  Abstracting USB worries me a
> bit though.  On the one hand, you want to abstract at the device level.

That would be a neat feature.  It'd require changes to the backend device 
driver to be a bit smarter about grabbing devices, as well as frontend 
changes to communicate device identities the backend...

> It's even hairer with virtualization though.  Say you had two harddrives
> that were USB and not uniquely identifiable.  You want to assign each
> harddrive to a separate VM.  If you unplug them and swap ports, and
> you're using the old configurations, you really want that each VM to see
> the harddrive they previously saw.  Swapping them could lead to
> confusion and even worse, security problems.

The current implementation sidesteps all these by specifying port IDs.  e.g. 
port 1 on my root hub always belongs to VM1 (when running), port 2 on hub 3 
always belongs to VM2 (when running), etc.

> Not sure the best solution here.  One of the reasons I've held off on USB.

For comparison, do you know what abstraction other systems do?  Do they assign 
ports or associate devices with VMs?

The latter is definitely an attractive option...  If we added support for both 
ways of doing things, paranoid people (or people with weird devices!) could 
use the port specifiers, whilst others used device IDs.

What do you think?


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