Re: C-kermit fails

[Florian Weimer via Libc-alpha <libc-alpha@sourceware.org>]

* Zack Weinberg:

> On Fri, Jul 24, 2020 at 3:41 PM Frank da Cruz <fdc@columbia.edu> wrote:
>> Somebody else sent a simpler patch, you can see it here:
>>
>> http://kermitproject.org/ckglibc228.diff
>
> This is still wrong, __FILE_defined is another implementation-use-only
> symbol, and it doesn't mean that the things you're actually trying to
> use are available.  (I am sorely tempted to delete it from the next
> release just to underline this point.)  If you need a stopgap for now,
> this is as correct as it gets:
>
> - #ifdef _IO_file_flags            /* Linux */
> + #if __GLIBC__ >= 2           /* GNU libc >= 2.0 */
>
> ... however, we are planning to stop exposing *any* of the internals
> of the FILE struct, Real Soon Now, at which point there will be
> nothing you can put here that will be correct.

I'm not sure if we can really do that (in the sense that there will be
nothing that works to replace this construct), but I completely agree
that this is undefined and should remain so.

If you do not like the stdio library, write your own I/O library (or use
another existing one).  Do not try to patch up the implementation using
internal details.

Keep in mind that each time you access library internals in this way,
you make it harder for us to make changes, including fixes for bugs you
might yourself have requested, because such changes may invalidate
existing programs.

Thanks,
Florian