Re: [TESTERS needed] New POSIX permission handling

[Corinna Vinschen <corinna-cygwin@cygwin.com>]

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On Apr 11 09:26, Ernie Rael wrote:
> I'm primarily a lurker, reading this list hoping things soak in a bit. So I
> may be off base on this.
> 
> In the table below, describing "NULL DENY access mask", looks like there's a
> typo concerning read/execute. (of course it might just be a windows mapping
> peculiarity that I really didn't want to know about ;-)

Hey, cool, somebody noticed :)
And since you asked, you'll get to know, whether you want or not ;)

> >The following bits in the NULL DENY access mask are used:
> >
> >   Windows access    <->   POSIX access
> >   --------------          ------------
> >   FILE_READ_DATA          S_ISVTX
> >   FILE_WRITE_DATA         S_ISGID
> >   FILE_APPEND_DATA        S_ISUID
> >
> >   FILE_READ_EA            MASK S_IXOTH  (POSIX execute perms)
> >   FILE_WRITE_EA           MASK S_IWOTH  (POSIX write perms)
> >   FILE_EXECUTE            MASK S_IROTH  (POSIX read perms)
> 
> Are read and execute swapped intentionally in the above?

Yes, indeed.  since the NULL access mask is not needed for actual
permission checking by Windows, we can use the bit as they fit our
needs.  The reason for using them in this order are their bit values.

  FILE_READ_EA  == 0x08       S_IXOTH == 0x01
  FILE_WRITE_EA == 0x10       S_IWOTH == 0x02
  FILE_EXECUTE  == 0x20       S_IROTH == 0x04

To convert from Windows to POSIX and vice versa, a simple shift
operation is sufficient.  Reordering just to fit the symbolic name
would complicate the conversion unnecessarily.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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