bug#13298: 24.3.50; Cannot write backup file; backing up in ~\.emacs.d\%backup%~

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sat, 29 Dec 2012 17:55:58 +0400
> From: Dmitry Gutov <dgutov@yandex.ru>
> CC: 13298@debbugs.gnu.org
> 
> On 29.12.2012 17:51, Eli Zaretskii wrote:
> >> Date: Sat, 29 Dec 2012 17:42:55 +0400
> >> From: Dmitry Gutov <dgutov@yandex.ru>
> >> CC: 13298@debbugs.gnu.org
> >>
> >>> Can you step with a debugger (e.g., Edebug) through
> >>> backup-buffer-copy, and see why it errors out?  My crystal ball says
> >>> it happens because of set-file-extended-attributes, in which case
> >>> please tell what is the value of extended-attributes argument passed
> >>> to backup-buffer-copy.
> >>
> >> Indeed, it happens after a call to set-file-acl.
> >>
> >> ((acl .
> >> "O:BAG:S-1-5-21-909999172-181315677-756075521-513D:(A;;FA;;;SY)(A;;FA;;;BA)(A;;FA;;;S-1-5-21-909999172-181315677-756075521-1000)")
> >> (selinux-context nil nil nil nil))
> >
> > And if, before the call to set-file-acl inside
> > set-file-extended-attributes, you evaluate the expression
> >
> >    (file-acl filename)
> >
> > what does it return?
> 
> "O:S-1-5-21-909999172-181315677-756075521-1000G:S-1-5-21-909999172-181315677-756075521-513D:(A;;FA;;;SY)(A;;FA;;;BA)(A;;FA;;;S-1-5-21-909999172-181315677-756075521-1000)"

I guess this happens because all of the following:

  . your user is a local Administrator

  . you took ownership of your ~/.emacs.d directory, instead of
    leaving it owned by the Administrators group

  . you didn't (or cannot) enable the "take ownership" privilege in
    your local security policy

Because of this, the files created inside ~/.emacs.d inherit the
owner of that directory, i.e. your user-id, while the original file
that is being backed up had the Administrators group as its owner
(that's what the "O:BA" part above means).  And because you don't have
the privileges of taking ownership, the call to set-file-acl fails.

I installed as trunk revision 111369 a set of changes that should fix
this for you.  Please test.  (I could only approximate the problem on
my machine, so I cannot be sure the changes indeed fix it.)