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

[Andi Kleen <ak@suse.de>]

> So I wander what goes on here- the syscall returns a long but
> libc cuts the high 32 bit?

System calls are always long, otherwise the syscall exit code cannot
check properly for signal restarts. 

glibc seems to indeed truncate. 

> 
> Now that I think about it,for compat if you start returning 0 in low
> 32 bits you are unlike to get the effect you wanted ...
> The ioctl_native could be changed but that would make it impossible
> for compatible ioctls to just use the same pointer in both.
> 
> So what do you think - should I make just the native ioctl a long,
> or both, and document that the high 32 bit are cut in the compat call?

both + document. 

> 
> > The main thing missing is documentation. You need clear comments what
> > the locking rules are and what compat is good for.
> 
> Would these be best fit in the header file itself, or in a new
> Documentation/ file?

Header file should be enough.

> > And you should change the code style to follow Documentation/CodingStyle
> I'll go over it again. Something specific that I missed?

e.g. your use of white space.

-Andi