Re: [Qemu-devel] [PATCH] Re-attach usb device to kernel while usb_host_open fails

[Gonglei]

On 2015/6/23 22:49, Lin Ma wrote:
> 
> 在 2015年06月23日 16:29, Gonglei 写道:
>> On 2015/6/23 12:24, Lin Ma wrote:
>>> Signed-off-by: Lin Ma <address@hidden>
>>> ---
>>>   hw/usb/host-libusb.c | 5 +++++
>>>   1 file changed, 5 insertions(+)
>>>
>>> diff --git a/hw/usb/host-libusb.c b/hw/usb/host-libusb.c
>>> index 10f4735..7258c4d 100644
>>> --- a/hw/usb/host-libusb.c
>>> +++ b/hw/usb/host-libusb.c
>>> @@ -888,6 +888,11 @@ static int usb_host_open(USBHostDevice *s, 
>>> libusb_device *dev)
>>>   fail:
>>>       trace_usb_host_open_failure(bus_num, addr);
>>>       if (s->dh != NULL) {
>>> +        qemu_remove_exit_notifier(&s->exit);
>>> +        QTAILQ_REMOVE(&hostdevs, s, next);
>> This change will cause a regression. For example, if an usb device's
>> (assume that it's usb1.0 device) speed does not match the ehci adapter,
>> then then invoking usb_host_open failed. if somebody changes the usb
>> device to an usb 2.0 device, it will not auto check because the device has
>> removed from the global hostdevs list.
>>
>> So I think we don't need  do the above operations.
> In this situation, in my opinion, User should perform device_add to add the 
> device again, Then the device will be added
> to hostdevs list and can be auto checked again, right?
> 
No, that's a regression if you ask users call device_add again.
The purpose that we use bus/port to identify one usb device is
can handle this scenario. After passing through one usb device by
usb/port, the guest can auto check the device though you changed a usb
device in the same physical port.

> In addition, The usb_host_open will be performed 3 times until 's->errcount 
> >= 3' while invoking usb_host_open failed.
> If the usb device isn't removed from hostdevs list, It will be detached & 
> re-attached 3 times.
> 
Yes, that's no problem as a protecting logic.

Regards,
-Gonglei
> 
> Thanks,
> Lin
>>> +        usb_host_release_interfaces(s);
>>> +        libusb_reset_device(s->dh);
>>> +        usb_host_attach_kernel(s);
>>>           libusb_close(s->dh);
>>>           s->dh = NULL;
>>>           s->dev = NULL;
>>>
>>
>>
>