To: Christopher Li <chrisl@vmware.com>
Cc: linux-usb-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org
Subject: Re: compat ioctl for submiting URB
References: <20050128212304.GA11024@64m.dyndns.org>
From: Andi Kleen <ak@muc.de>
Date: Sat, 29 Jan 2005 07:33:31 +0100
In-Reply-To: <20050128212304.GA11024@64m.dyndns.org> (Christopher Li's
 message of "Fri, 28 Jan 2005 16:23:04 -0500")
Message-ID: <m1llaclp6s.fsf@muc.de>
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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

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