Re: [PATCH v5 1/2] libxl: Introduce functions to add and remove USB devices to an HVM guest

[George Dunlap <george.dunlap@eu.citrix.com>]

On 19/04/13 12:00, George Dunlap wrote:
> On 19/04/13 11:50, Ian Campbell wrote:
>> On Fri, 2013-04-19 at 11:18 +0100, George Dunlap wrote:
>>> We could add an option that says "attempt to do the remove even if
>>> you
>>> don't see the device in xenstore" I suppose.  But I'm not really sure
>>> how to document that in a useful way without basically describing the
>>> internal mechanics of the command.
>>>
>>> There's nothing we can really do about usb-list though.
>> You could write it to xenstore before attempting the qmp commands. That
>> just relies on the qmp remove failing gracefully for devices which
>> aren't actually attached.
> qmp remove will just return an error if you attempt to remove a device
> id it doesn't know about.  I suppose that could work.  It's also a bit
> more robust against, say, the xenstore add failing for whatever reason.

Hmm, if the qmp_remove fails, we don't know if that's because because 
the device didn't exist, or because it failed for some other reason.   
If qmp remove fails, we shouldn't touch the xenstore entry.

So I think you get in to the same basic problem here, except that you 
get an un-removeable xenstore entry instead of an unremoveable USB device.

  -George