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

[H. Peter Anvin]

Miklos Szeredi wrote:
> On Thu, 28 Aug 2008, H. Peter Anvin wrote:
> > This is *hard* to get right, and we screw this up in the kernel with 
> > painful regularity.  The throught of having user-space processes, which 
> > don't have access to the kernel locking primitives and functions like 
> > copy_from_user() dealing with this stuff scares me crazy.
>
> What issues exactly are you thinking of?

Memory changing underneath you.  It can be dealt with by very careful 
sequencing only.

> > That is why I'm suggesting using an in-kernel linearizer.
>
> Lots of complexity, ugh...  Even Tejun's current scheme is better IMO.

And then you get *no* privilege separation, for one thing, so why even 
bother doing it in userspace?

	-hpa
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