linux-kernel - Re: [PATCH 5/7] FUSE: implement ioctl support

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Message-ID: <48B6E844.3050508@kernel.org>
Date:	Thu, 28 Aug 2008 20:02:44 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Greg KH <greg@...ah.com>
CC:	fuse-devel@...ts.sourceforge.net, miklos@...redi.hu,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/7] FUSE: implement ioctl support

Tejun Heo wrote:
> Greg KH wrote:
>> Why do we need ioctls?  For CUSE?  In that case, would we need to copy
>> the memory from userspace, into the kernel, and then back out into
>> userspace again?  Can't we just have a "pass-through" type fixed ioctl
>> instead?
> 
> Can you elaborate a bit?  How the fixed ioctl would know how much to
> copy in and out and from where?

If you're worried about the double copying due to performance reasons,
what we can do is implementing userspace to userspace copying.  I just
took easier path of copying twice as u-u copy can't be done using the
existing FUSE mechanics, but frankly, at this point, I think that would
be an premature optimization.

-- 
tejun
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