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

viro
2004-09-01T07:32:36Z

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

Too bad.

> 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.
>
> Further, adding a command to the ioctl suddenly requires changing
> two places - registration code and ioctl itself.

So don't add them. Adding a new ioctl is *NOT* a step to be taken lightly -
we used to be far too accepting in that area and as somebody who'd waded
through the resulting dungpiles over the last months I can tell you that
result is utterly revolting.

Excuse me, but I have zero sympathy to people who complain about obstacles
to dumping more into the same piles - it should be hard.