Re: [libusb] Can't write to a control endpoint in libusb-1.0.16_RC10, when bulk transfer (printing) is going on in interface 0

[Hans de G. <hde...@re...>]

Hi Alan et al,

On 06/28/2013 05:15 PM, Alan Stern wrote:
> On Fri, 28 Jun 2013, Kumar, Sanjay wrote:
>
>> Hello Hans,
>>
>> After all the analysis from our side we believe that, it will be good if fix is provided in kernel (always allow the get_device_id printer request).
>>
>> Below are the calls for which we need this fix in the kernel.
>>
>>                 1. Used for getting device ID
>> 	rlen = libusb_control_transfer(hd,
>> 			LIBUSB_ENDPOINT_IN | LIBUSB_REQUEST_TYPE_CLASS | LIBUSB_RECIPIENT_INTERFACE, /* bmRequestType */
>> 			LIBUSB_REQUEST_GET_STATUS,        /* bRequest */
>> 			config,        /* wValue */
>> 			interface, /* wIndex */
>> 			buffer, maxSize, LIBUSB_CONTROL_REQ_TIMEOUT);
>>
>>                 2. Used for getting device status for some printers.
>> 	len = libusb_control_transfer(hd,
>> 			LIBUSB_ENDPOINT_IN | LIBUSB_REQUEST_TYPE_CLASS | LIBUSB_RECIPIENT_INTERFACE, /* bmRequestType */
>> 			LIBUSB_REQUEST_CLEAR_FEATURE,        /* bRequest */
>> 			0,        /* wValue */
>> 			interface, /* wIndex */
>> 			&byte, 1, LIBUSB_CONTROL_REQ_TIMEOUT);
>>
>> And regarding the older kernels HPLIP users will see issues only when libusb version is > 1.0.9. I think that is fine for us as we can provide a hot fix to users falling in this category. But this fix will ensure that all future Distros have this fix present in the kernel . Please let us know your thoughts on this. Also please provide the kernel patch whenever available, so that we can test it here. Thanks again for all the help.
>
> The kernel does not allow more than one program or driver to use an
> interface at any time.  This means that while the HPLIP program uses
> the printer interface, other programs cannot use it.

I was hoping that we could make life easier for the hplip people (and
possible other printer related userspac), by simply always allowing
REQUEST_GET_STATUS on printer-class interfaces. We already have special
handling for this request in check_ctrlrecip, changing this to always
allow is trivial, and it is a read-only request.

I was not aware they were going to need LIBUSB_REQUEST_CLEAR_FEATURE too.

Sanjay, if you need REQUEST_CLEAR_FEATURE to work too, you will need to
do what Alan says and have some sort of daemon talking to / owning the
interface, and have all apps which need access to the interface talk
to the daemon.

Regards,

Hans