[Libusb-devel] "error submitting URB: Invalid argument" on bulk reads

[Throctukes <jus...@gm...>]

I have a USB device (a custom device I'm trying to talk to) with two
endpoints, one writing to the device, one reading from the device. Both are
bulk transfers. Every communication transaction takes the form of (1) Write
a command to the device (2) Read the response. I'm using libusb 0.1.12

On Windows, all is well. I can connect the device, claim the interface and
communicate happily. However, in Ubuntu (a standard Hardy desktop install),
whilst I can connect to the device and write to it, all read operations fail
with the error "error submitting URB: Invalid argument" reported from libusb
(error code -22).

If I check /var/log/messages I see a warning message logged for the same
time as the read was attempted: "sysfs: duplicate filename 'usbdev4.3_ep81'
can not be created" - which tallies with the device (it is indeed on that
bus and it's endpoint 81 I'm trying to read from). Dunno if that's relevant.

I've been trying to figure out what I'm doing wrong for days now - has
anyone got any ideas where I should even be looking for the problem? I
noticed that someone else reported a similar issue, but found that it was
because their endpoint was really in interrupt, not bulk, mode. I'm pretty
sure that's not the case here.
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