[PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag

[Al Viro]

On Sat, Sep 19, 2020 at 05:14:41PM -0700, Andy Lutomirski wrote:

> > 2) have you counted the syscalls that do and do not need that?
> 
> No.

Might be illuminating...

> > 3) how many of those realistically *can* be unified with their
> > compat counterparts?  [hint: ioctl(2) cannot]
> 
> There would be no requirement to unify anything.  The idea is that
> we'd get rid of all the global state flags.

_What_ global state flags?  When you have separate SYSCALL_DEFINE3(ioctl...)
and COMPAT_SYSCALL_DEFINE3(ioctl...), there's no flags at all, global or
local.  They only come into the play when you try to share the same function
for both, right on the top level.

> For ioctl, we'd have a new file_operation:
> 
> long ioctl(struct file *, unsigned int, unsigned long, enum syscall_arch);
> 
> I'm not saying this is easy, but I think it's possible and the result
> would be more obviously correct than what we have now.

No, it would not.  Seriously, from time to time a bit of RTFS before grand
proposals turns out to be useful.