Re: is this a bug in glibc or readpst?

[Florian Weimer <fweimer@redhat.com>]

* Paul Wise:

> On Wed, 2022-11-23 at 09:57 +0100, Florian Weimer via Libc-help wrote:
>
>> Fork still shares the underlying file description.  It only duplicates
>> the descriptors.  If the subprocess changes the file pointer back to 0,
>> it will affect the original process, too.  This is just how file
>> descriptors work.
>> 
>> Could this explain the issue?
>
> That does sound like what the symptoms would indicate.
>
> However it doesn't seem to fit, because the first thing the child
> process does is call freopen(), which should in theory close the
> descriptor and then create a new file descriptor and file description?
>
> On the other hand, the fact that using fclose()+fopen() instead of
> freopen() does seem to fix the problem, seems to indicate that
> freopen() is not actually successfully closing the descriptor and
> thus the file pointer is shared between processes?

Could you run it under strace -k, with debuginfo?  Hopefully that will
shed some light on the problem.

Thanks,
Florian