(call-process ...) hangs in emacs

[Eric Blake]

On 08/27/2014 09:15 AM, Achim Gratz wrote:
> Ken Brown <kbrown <at> cornell.edu> writes:
>> Achim, could you send me a recipe for reproducing the problem so that I 
>> can test further?  Please be very detailed; I have no experience with ACLs.
> 
> Let's get one issue out of the way first that may be a Cygwin bug: on Linux
> a file with all access removed via standard POSIX modes and then access
> granted via ACL would place the mask bits of the ACL (the maximum permission
> that can be granted via ACL, usually rwx) into the group portion of the
> POSIX modes (ls --color would even show these in different color if you
> didn't happen to notice the "+").  That doesn't happen on Cygwin and it
> seems that some software optimizes based on that information to not traverse
> the ACL when there's no chance to ever get a permission granted.  This
> behaviour is mandated by POSIX IIUC (and it is what Linux is doing) so
> unless Cygwin explicitly follows a different ACL model, I think that should
> be taken care of before diving into this further.

Sadly, POSIX doesn't mandate ACLs (in part because there are so many
differing implementations that it was impossible to standardize a common
ground).  So code using ACLs across multiple platforms has to deal with
quirks, and although gnulib attempts to do so, it may be a shortcoming
in the gnulib wrappers that emacs is using.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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