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

[Glenn Morris]

Artem Chuprina wrote:

> Having org on ext4 filesystem with 0664 permission on org/work.org, and
> c1 on FAT filesystem with file permissions 0075 (in fact, SD card on
> Android system, so such strange permissions) I do
>
> M-: copy-file("org/work.org" "c1/work.org" t)
>
> and get an error
>
> Debugger entered--Lisp error: (file-error "Doing chmod" "operation not
> permitted" $

I'm not sure this is a bug.
The file is copied, but there is an error trying to preserve permissions.
Because eval-expression-debug-on-error is non-nil by default, the
debugger pops up.

Emacs's behaviour seems the same as using

cp -a org/work.org c1/work.org

on the command-line. "-a" is appropriate because C-h f copy-file says:

  This function always sets the file modes of the output file to match
  the input file.