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

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.

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

Rasmus