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

[Bill Davidsen]

viro@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx wrote:
> 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.

I don't think he was complaining so much as providing a rationale for 
the patch he offered which is intended to make things better. Seemed to 
me like a good context for the patch.

--
   -bill davidsen (davidsen@xxxxxxx)
"The secret to procrastination is to put things off until the
 last possible moment - but no longer"  -me
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