Re: [Qemu-devel] qapi: [PATCH v2] Implement query-usbhost QMP command

[Alexander Kappner]

Hi Gerd,

thanks for reviewing. I'll follow up with a v3 of the patch addressing your 
proposed changes.

>> This allows a QMP client to query which USB devices may be available
>> for redirection.

> At least libvirt sandboxes qemu, for security reasons, and you wouldn't
> get any useful results because qemu hasn't the permissions needed to
> scan the usb bus.
Then at least this tells you that you can't make anything available via 
redirection either, which is also useful information.

> I'm wondering what the use case is?
I'm working on a smartphone client that talks to a QEMU instance via QMP, and 
that allows the user to switch USB devices between host and QEMU guest. This 
removes the need for a separate set of input devices permanently assigned to 
the host (since if I pass through a keyboard/mouse to the VM, I can't use that 
same keyboard/mouse to run a command that re-attaches those devices to the 
host, so I need some external channel). Basically using the phone as a KVM 
switch.

Best
Alexander

On 04/16/2018 01:29 AM, Gerd Hoffmann wrote:
> On Sat, Apr 14, 2018 at 02:29:34AM -0700, Alexander Kappner wrote:
>> Implement a QMP command similar to the HMP's "info usbhost" command.
> 
> The hmp version of the command should be switched over to call the
> qmp_query_usbhost() and pretty-print the qapi struct then, to make
> sure hmp and qmp versions of the command deliver consistent results.
> 
>> This allows a QMP client to query which USB devices may be available
>> for redirection.
> 
> I'm wondering what the use case is?
> 
> At least libvirt sandboxes qemu, for security reasons, and you wouldn't
> get any useful results because qemu hasn't the permissions needed to
> scan the usb bus.
> 
>>  ##
>> +# @query-usbhost:
>> +#
>> +# Returns information about USB devices available on the host
>> +#
>> +# Returns: a [UsbDeviceInfo]. Returns an error if compiled without
>> +# CONFIG_USB_LIBUSB
>> +#
>> +# Since: TODO (maintainer insert version number if mainlined)
> 
> Will not make it into 2.12, so 2.13.
> 
>> +# @UsbDeviceInfo:
>> +#
>> +# @speed: the speed
> 
> Use an enum for this?
> 
>> +# @id_vendor: idVendor field from device descriptor
>> +#
>> +# @id_product: idProduct field from device descriptor
>> +#
>> +# @str_product: string descriptor referenced by iProduct index, if any
>> +#
>> +# @str_manufacturer: string descriptor referenced by iManufacturer index, 
>> if any
>> +#
>> +# @dev_addr: address on bus that device is connected to
>> +#
>> +# @bus_num: bus number device is connected to
> 
> No port?
> 
> cheers,
>   Gerd
>