What is wrong with FreeBSD and USB Support

Hans Petter Selasky hps at selasky.org
Mon Mar 6 10:26:05 UTC 2017

On 03/06/17 06:19, Markus Rechberger wrote:
> Hi,
> I have been trying to port a driver to freebsd for a day now and the
> result is quite negative.
> So my feedback about libusb20 and the FreeBSD USB Kernel Stack:
> 1. the documentation is not clear how to set up asynchronous bulk
> transfers (please explain the architecture of this API)
> 2. the errors returned by libusb20 (and probably from the kernel) are
> not detailed enough (in certain cases I'm able to get libusb20 unknown
> error, to my understanding every error should have some meaning).
> 3. the FreeBSD USB Stack messes around with the transfer itself
> damaging the entire result (eg resulting in stalled USB bulk
> transfers).
> 4. The FreeBSD data transfer implementation itself is a disaster, I'm
> able to transfer data at a rate of 2 MB/sec, anything higher results
> in a stalled usb transfer?!
> 5. USB Control messages are 100% slower than with other operating
> systems (eg. it took 14 seconds to load a driver with FreeBSD while it
> only takes 7 seconds on other systems).
> Since I have been using USB stacks with Linux, Mac and some other
> systems I can say that FreeBSD has the most irritating implementation
> of all.
> So finally I wonder what is wrong with FreeBSD's USB support?


Can you share some code and/or USB traces from "usbdump" for the slow 
traffic pattern. I'm pretty sure this isn't a FreeBSD problem, but how 
you use the APIs in FreeBSD's USB stack improperly.

Further, which version of FreeBSD is this?

Last but not least, if you are not observing 100% CPU usage on a CPU 
core during testing, it is for sure not a problem with the USB stack 
and/or IOCTL APIs.


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