bug#24656: 25.1; Emacs leaves lock files on a CIFS share

[Paul Eggert <eggert@cs.ucla.edu>]

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On 10/11/2016 10:07 AM, Eli Zaretskii wrote:
> Sounds fine to me.  I just tried this on a Windows filesystem, and it
> allows that, so Samba should, too.

Unfortunately when I looked at the Emacs code more carefully, I found 
that '..' won't work because it will confuse older Emacs. So will '@'. 
Come to think of it, changing conventions in this area is likely to 
break interoperability not only with older Emacs, but also with other 
programs that attempt to work with Emacs's locking scheme.

I looked into Cygwin, and it seems to use U+F022 to represent '"', not 
':'. So this is not Cygwin-related.

I looked at the original Red Hat bug report, and found that I could 
reproduce the problem with a simple C program, i.e., without Emacs or 
Cygwin. It appears to be a Samba bug. I added a comment to that effect 
to the Red Hat bug report.

I installed into Emacs master the attached patch, which should work 
around the Samba bug without introducing so many interoperability 
hassles, and am boldly marking the Emacs bug as done. It's not clear to 
me whether this change is worth backporting into emacs-25, as Emacs has 
locked files this way for ages.

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