Re: [PATCH] err_ptr.h: introduce ERR_PTR_SAFE()

On Mon, May 18, 2026 at 11:04 AM Rasmus Villemoes <[email protected]> wrote:
>
> On Sat, May 16 2026, Amir Goldstein <[email protected]> wrote:
>
> > On Sat, May 16, 2026 at 10:42 AM David Laight
> > <[email protected]> wrote:
> >>
> >> On Fri, 15 May 2026 21:26:04 +0200
> >> Amir Goldstein <[email protected]> wrote:
> >>
> >> > On Fri, May 15, 2026 at 8:30 PM David Laight
> >> > <[email protected]> wrote:
> >> > >
> >> > > On Thu, 14 May 2026 22:01:29 +0200
> >> > > Amir Goldstein <[email protected]> wrote:
> >> > >
> >> ...
> >> > >
> >> > > The object code bloat would be noticeable if this were used everywhere.
> >> > > But you could make it a bit simpler:
> >> > >         if (__builtin_constant_p(__e))
> >> > >                 BUILD_BUG_ON(__e && !IS_ERR_VALUE(__e));
> >> > >         else if WARN_ON(__e && !IS_ERR_VALUE(__e))
> >> > >                 __e = -MAX_ERRNO; // Or maybe -EINVAL to stop and other boundary errors
> >> > >         (void *)__e;
> >> >
> >> > Yeh that's nicer thanks.
> >>
> >> Actually this might be better still (or just more succinct):
> >>         void *__e = (void *)error;
> >>         BUILD_BUG_ON(!statically_true(IS_ERR_OR_NULL(__e));
> >
> > This condition is wrong but also my compiler does not evaluate
> > __builtin_constant_p(IS_ERR_OR_NULL(__e)) as true.
> >
> > This works
> > BUILD_BUG_ON(statically_true(!IS_ERR_VALUE(__e)));
> >
> > I think it is enough to statically assert on ERR_PTR(EINVAL)
> > and no need to bother with ERR_PTR(0)
> >
> >>         if (WARN_ON(!IS_ERR_OR_NULL(__e))
> >>                 __e = (void *)-EINVAL;
> >
> > Oh, anything but EINVAL please - the most overloaded error value
> > My choice of meaningful error value would be EFAULT
>
> Could we have a dedicated "EBUG" that can be used to indicate "there's a
> bug somewhere in the kernel, we can handle it somewhat gracefully here
> by returning an error instead of BUG(). You can't do anything about it
> but report that you got -EBUG from $this_syscall", instead of
> overloading EIO, EFAULT, EINVAL or whatnot. Internally, EBUG could be a
> macro that did ({ WARN_ONCE(); -__EBUG; }) or something, so there would
> automatically be bread crumbs in dmesg if it is ever hit.

How exactly would you use this EBUG() to write the graceful handling?
A bit of overengineering if you ask me.

>
> Userspace code could also benefit from having EBUG to indicate that some
> internal inconsistency has been detected.

So what about

#define EBUG MAX_ERRNO

as per my suggested patch.

Thanks,
Amir.