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

Bill Davidsen
2004-09-01T18:08:43Z

viro@parcelfarce.linux.theplanet.co.uk 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@tmr.com)
"The secret to procrastination is to put things off until the
last possible moment - but no longer" -me