NatFeats USB: Transfer size of bulk transfers not returned to Atari side

[czietz]

The NatFeats call USBHOST_SUBMIT_BULK_MSG returns the return value of libusb_bulk_transfer() but not the number of bytes transferred:

aranym/src/natfeat/usbhost.cpp

Lines 841 to 846 in 880e24d

	r = libusb_bulk_transfer(devh[dev_idx], endpoint, tempbuff, len, &transferred, timeout < 1000 ? 1000 : timeout);
	D(bug("USBHost: return: %d len: %d transferred: %d", r, len, transferred));
	return r;
	}

However, the FreeMiNT driver uses this return value to populate dev->act_len, the actual transfer length:
https://github.com/freemint/freemint/blob/f42d8b22ebc68a60377eebfc7d7f60ccf77c823c/sys/usb/src.km/ucd/aranym/aranym-hcd.c#L225-L244

As the libusb documentation explains, the return value can be (among others)

0 on success (and populates transferred)
LIBUSB_ERROR_TIMEOUT if the transfer timed out (and populates transferred)

... which means that dev->act_len is filled incorrectly.

Imho, the NatFeats call should return transferred in these two cases and and a (negative) error in all other cases to the FreeMiNT driver.

[DavidGZ]

@czietz you're right, this must be fixed, probably the confusion came from that libusb_control_transfer() function actually returns the number of bytes transferred on success.

Thanks for spotting this.

[th-otto]

Hm, but when libusb always populates *transferred, then returning a single value from the call might not be good enough.

[DavidGZ]

This has been fixed with 88f4713

Thanks @czietz for pointing to this bug.