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

[Marek Marczykowski <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

On 20.03.2013 19:26, Ian Jackson wrote:
> George Dunlap writes ("Re: [Xen-devel] [PATCH 1/2] libxl: Introduce functions 
> to add and remove host USB devices to an HVM guest"):
>> There are some semantic differences that I think are important (or could 
>> be important).  One big one is that PVUSB appears to require the caller 
>> to specify the virtual topology used, while with qemu it is not possible 
>> to specify the virtual topology.  This gives us a few options for a 
>> unified interface:
> 
> The obvious answer to this is to make specifying the virtual topology
> optional in the unified syntax.
> 
> (TBH I'm not sure why anyone would ever want to specify a particular
> virtual topology.  I'm sure most people would prefer just to let the
> tools set something up.)

Yes, specifying topology by hand (which basically means creating one USB 1.1
bus and one USB 2.0 bus) is only inconvenience in PVUSB. It should be done
automatically.

>> PVUSB also (it seems) requires devices to be assigned to usbback before 
>> they can be given to guests.  So in the pv case, device_add() would have 
>> to do assign then attach, and device_del would have to do detach then 
>> de-assign.  That's probably not so bad.
> 
> I definitely think this should happen automatically.

Indeed. This is one/two writes to sysfs. One possible difficulty: backend can
be in some domU instead of dom0, but then IMHO assigning device to usbback can
be left to the user.

But important thing: interface needs to allow specify (optional) backend
domain in addition to device itself (with default to dom0). Same as other
interfaces like block or network.

-- 
Best Regards / Pozdrawiam,
Marek Marczykowski
Invisible Things Lab

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