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jiegec / usbip

A Rust library to run a USB/IP server
MIT License
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usb write does not return correct URB response #13

Closed jamesadevine closed 1 year ago

jamesadevine commented 1 year ago

Hey!

It looks like when returning a URB response to an IN request, you need to write the length of the bytes written as the urb data length:

image

https://www.kernel.org/doc/html/latest/usb/usbip_protocol.html

Currently, we use the returned response, which in the case of a write is an empty vector. So if a driver etc. writes n bytes and expects n to be returned, it will always see 0.

I have a patch but it is, as per usual, not a small one...

jamesadevine commented 1 year ago

Would be good to double check my assertion above. I think the docs are a bit misleading here.

jamesadevine commented 1 year ago

Certainly, it was the case for me that a driver was blocked waiting for a write to complete successfully. Is there a kernel driver we can learn from?

jamesadevine commented 1 year ago

The docs are not misleading if you use your brain to read them :smile: silly me...

I interpreted it as in the case where the direction is USBIP_DIR_OUT, n is 0, therefore, one would assume actual_length should also be zero. What it actually says is that for USBIP_DIR_OUT, actual_length is always the length of the origin URB transaction. In the case where the direction is USBIP_DIR_OUT, n is 0, because there is no payload; actual_length is still the length of the URB transaction..