Re: [Xen-devel] [PATCH V4 3/7] libxl: add pvusb API

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Tue, Jun 16, 2015 at 11:56 AM, JÃrgen Groà <jgross@xxxxxxxx> wrote:
> On 06/16/2015 12:41 PM, Ian Jackson wrote:
>>
>> George Dunlap writes ("Re: [Xen-devel] [PATCH V4 3/7] libxl: add pvusb
>> API"):
>>>
>>> Ian / Ian / Wei / Jim:
>>
>>
>> Hi.
>>
>>> 3. Have the libxl layer accept both busid and bus:addr.  Translate as
>>> necessary and store in the libxl_device_usb struct.
>>
>> ...
>>>
>>> The advantage of #3 internally is that the functions can do the
>>> translation once (if necessary), and can then pass around the public
>>> libxl_device_usb struct as-is without needing any extra parameters or
>>> a separate libxl_device_usb_internal.  The disadvantage, I think, is
>>> that from an interface perspective, it's fairly pointless to have
>>> both.  busid doesn't really give you any better or more control than
>>> the other, and it's not any more convenient for the user (in fact it's
>>> less convenient because it's more difficult to find).
>>
>>
>> Is the busid more stable in the face of plug/unplug ?  This is the
>> normal reason for a more path-like device specification.
>>
>> If so then we must support it, even if it's not the usual way an
>> ordinary user would use it for a one-off.  Otherwise you have to write
>> something in your config files for the VMs on your VM host, which will
>> break when someone plugs a keyboard into the `wrong' USB port.
>
>
> Unfortunately the busid isn't stable at least across reboots.

Isn't it based on the physical topology of the USB network?  Shouldn't
it be the same as long as you don't actually unplug anything?

 -George

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