Re: [discuss] f_ops flag to speed up compatible ioctls in linux kernel

Andi Kleen
2004-09-03T08:02:44Z

On Wed, Sep 01, 2004 at 10:22:45AM +0300, Michael S. Tsirkin wrote:
> Hello!
> Currently, on the x86_64 architecture, its quite tricky to make
> a char device ioctl work for an x86 executables.
> In particular,
> 1. there is a requirement that ioctl number is unique -
> which is hard to guarantee especially for out of kernel modules

Yes, that is a problem for some people. But you should
have used an unique number in the first place.

There are some hackish ways to work around it for non modules[1], but at some
point we should probably support it better.

[1] it can be handled, except for module unloading, so you have
to disable that.

> 2. there's a performance huge overhead for each compat call - there's
> a hash lookup in a global hash inside a lock_kernel -
> and I think compat performance *is* important.

Did you actually measure it? I doubt it is a big issue.

-Andi