Re: compat ioctl for submiting URB

[Andi Kleen <ak@muc.de>]

Christopher Li <chrisl@vmware.com> writes:

> VMware is a big user of the usbdevfs, we translate guest USB
> IO to usbdevfs, by submitting URB. On the x86_64 system, we
> need those compatible ioctl for submitting URBs. For now we
> make a hack to submit it through the vmmon driver. But that
> is very ugly. 
>
> I do want this problem get fixed in the linux kernel eventually.
> I have been toying with two different ways to solve it. It seems
> that it is unavoidable to get hands dirty in the usbdevfs internals.
> The first one is just educate the usbdevfs to know about the 32 bit
> URB ioctls. So it don't need to keep around a bounce buffer.

Looks reasonable from a first look.

Issues:
- Should use CONFIG_COMPAT, not x86-64 specific symbols
- Why can't you set URB_COMPAT transparently in the emulation
layer?  Then existing applications would hopefully work without
changes, right?

You may also want to preserve the __user casts, otherwise
Al Viro and other sparse users will be unhappy.

Thanks for attacking this long standing problem.

-Andi