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

[ebiederm@xmission.com (Eric W. Biederman)]

Tejun Heo <tj@kernel.org> writes:

> Hello,
>
> Miklos Szeredi wrote:
>>> So why not just only support well defined ioctls and serialize them
>>> in the kernel and allow the receiving process to deserialize them?
>> 
>> I'd like the idea of limiting to well behaved ioctls, but Tejun
>> doesn't...
>
> I'm not dead against it.  I'm just a bit more inclined to my
> implementation (naturally), which means if you're dead against the
> current implementation, supporting only the proper ones definitely is
> an option, but comparing the pros and cons, I'm not quite convinced
> yet.

I really think that if an ioctl is passing through the kernel we
should know how to parse and understand it's options.  Otherwise
we won't have the option of doing backwards compatibility when something
changes, like we can with the 32->64bit ioctls.

That seems to imply that you need a stub in the kernel to handle 
really weird ioctls.

The upside is that because you know what the inputs and outputs are
and where the inputs and output are you can support that ioctl well
into the future, and you can do it with an unprivileged file
system server.

Eric