RFR: 8293004: (fs) copy_file_range needs fallback handling for ENOSYS

[Thomas Stüfe]

Thanks for the clarification, Florian!

..Thomas

On Sat, Aug 27, 2022 at 2:45 PM Florian Weimer <fweimer at redhat.com> wrote:

> * Thomas Stüfe:
>
> > do I understand this correctly: by backporting the user-space
> > emulation for copy_file_range, glibc 2.27 broke compatibility with
> > kernels < 4.5?
> >
> > If yes, why did glibc not retain the emulation for the ENOSYS case?
>
> The emulation was buggy in corner cases, and the kernel kept changing
> behavior, too.  With the current implementation, an application can
> decide whether they want to roll their own slightly dodgy copying loop
> if there is no kernel support.  With the emulation present, that wasn't
> possible.
>
> (Not sure if the <fweimer at openjdk.org> address works.)
>
> Thanks,
> Florian
>
>
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