Hi Alan, I'm working on implementing a USB proxy that uses libusb on one side and Raw Gadget on the other. The idea is to pass all requests received from the host via Raw Gadget to the proxied device via libusb and report back the responses. However, I've stumbled upon an issue with non-0-length control requests that get stalled by the proxied device. To pass an OUT control request to the device via libusb I need to first retrieve the data for the request from the host. And with Raw Gadget I can do that via USB_RAW_IOCTL_EP0_READ, which internally calls usb_ep_queue, waits for its completion, and copies the data to userspace. But the problem is that once I retrieve the data, the request is automatically acked. Thus, if the proxied device stalls the request, it's already too late to stall it via Raw Gadget. AFAIU, GadgetFS works the same way. Is there a way to work around this? If this requires a change is Raw Gadget, that is fine. But I'm wondering if this is possible to do at all with the USB Gadget API: AFAIU, we have to either stall or retrieve the data; we cannot do both. If this is indeed impossible, perhaps you know if there's a way to directly use usbfs to separately submit the control request header to the proxied device to figure out if it wants to stall? And only then retrieve the data from the host via Raw Gadget if the device doesn't stall. Thank you!
