[Spice-devel] [spice-gtk PATCH 0/9] Windows: identify USB devices by vid:pid instead of bus.address

[Uri Lublin]

On 03/25/2013 12:17 PM, Hans de Goede wrote:
> Hi,

Hi Hans,

Thanks for reviewing.

>
> On 03/25/2013 11:01 AM, Uri Lublin wrote:
>> rhbz#842816
>>
>> It seems that sometimes a USB device's bus.address is changing after
>> installation of WinUSB driver for that device.
>> So instead use vid:pid which are consistent across driver installation.
>>
>> The switch to using vid:pid is done in patch 8/9.
>>
>> Some code reuses variables named "bus" and "address" to hold vid and pid
>> values. If people think this should be changed to new variables names 
>> (ifdefed)
>> and/or new function instead of 
>> spice_usb_device_manager_get_udev_bus_n_address
>> let me know.
>>
>> Using two devices with the same vid:pid on the same Windows client is 
>> already
>> not supported, since Windows installs USB drivers for specific devices
>> based on their vid:pid
>
> Hmm, I'm not very happy with the approach you've chosen here. Just 
> because
> usbclerck / our driver swapping magic currently does not support 
> having devices
> with identical vid:pid is not a good reason to add the same problem to 
> other
> parts of the code. The contrary is true really, this is something 
> which we
> should try to fix, not make worse.

I'm only trying to fix the Windows bus.addr inconsistency problem.
I don't think that makes things worse, but better.
I agree that this patch-set inserts the existing driver limitation
(of using two devices with the same vid:pid) into spice-gtk,
for Windows (and keeps Linux as is).
This limitation already exists for Windows clients, and
we can remove it from spice-gtk in the future if needed.

>
> Have you tried using libusb_get_port_path? I know that is sensitive to
> device swap races on the same port, so how about using a combination of
> libusb_get_port_path + vid & pid to identify a device?

I did not try using libusb_get_port_path.
It may be a better solution:
  - It works the same for both Linux and Windows.
  - It fixes the Windows problem (all should be consistent through 
driver install)
  - It is a more robust solution for Linux (is it really ?).
    + Wouldn't device_address change upon device_swap ?
It's also requires a bit more memory.

We'd need to use bus_number as part of device identification.
There may be two different devices on two different buses that have
the same port_path (at least that's the case on Linux).

This seems like a feature (bug?) of libusbx:
I changed libusbx's examples/listdevs.c to print port_number and port_path
and plugged the same device on my machine's ports (diff attached):

$ ./listdevs | grep 0457
0457:0151 (bus 1, device 26 port=1) (port_path[2]={1 1 }
$ ./listdevs | grep 0457
0457:0151 (bus 2, device 7 port=1) (port_path[2]={1 1 }

So the identifier must be vid:pid, bus_number, port_path.

Thanks,
     Uri.


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