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

[Tejun Heo <tj@kernel.org>]

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