bug#16133: 24.3; copy-file fails on chmod when copying to FAT filesystem

[Paul Eggert]

Artem Chuprina wrote:
> With copy-file in emacs24 I just cannot write such code

It's certainly *possible* to write such code: just catch
the error and continue.

> much code that used copy-file before, just stopped working.  (I've
> mentioned org-mobile-push, and emacs' own file backup code

This is a more serious matter, but it's a judgment call as to
whether it stopped working or started working.  Some users
want permissions to be saved, as well as contents.  Others
don't.  Emacs should support both usages.

I'm still puzzled as to why you're observing the problem and
I am not.  Can you do an 'strace' on an Emacs that's exhibiting
the problem?  It'd be helpful to see exactly which system calls
are being invoked, and the errno value for the failing one.
Possibly there is a small workaround here that wouldn't require
redesining copy-file.