Description:
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The filesystem commands is_writable / is_readable / is_executable are now using stat() instead of access(), which doesn't return accurate results in a number of situations:

    - on many network filesystems
    - if the system uses ACLS
    - if you have more groups than just initgroups

The current version only works on simple (unextened) unix filesystem - filesystems that only use the traditional unix octets for access control.

the filesystem commands that check file system access should be based on access() instead of stat():

http://www.opengroup.org/onlinepubs/009695399/functions/access.html

Acc'd to CVS the is_writable stuff changed when php_stat was routed through the streams API:

http://cvs.php.net/diff.php/php-src/ext/standard/filestat.c?r1=1.127&r2=1.128&ty=h

There's a bug report from a couple of years ago that suggests adding an access() command to the posix extention:

http://bugs.php.net/bug.php?id=14924

If you want to keep the functionality gained by routing php_stat through the streams API, how about offering access() through the posix commands?