Mail Archives: cygwin/2011/04/06/19:35:10
-----Original Message-----
From: Cygwin On Behalf Of Larry Hall (Cygwin)
Sent: Wednesday, 6 April 2011 11:04 AM
Subject: Re: NTFS write-protect flag translation (tar? rsync?) only one-way?
>On 4/5/2011 8:35 PM, Christian Gelinek wrote:
>> From: Cygwin On Behalf Of Larry Hall (Cygwin)
>>> On 4/5/2011 3:36 AM, Christian Gelinek wrote:
>>>> It appears that when tar reads files for adding to archives, it
>>>> correctly interprets the Windows-set "R" attribute, which is also seen=
by
>>>> ls under Cygwin. After extracting the files using tar though, only
>>>> Cygwin's ls command seems to be aware of the read-only attribute; the
>>>> attrib command (as well as Explorer and other Windows-apps) see and
>>>> handle the file as being writeable.
>>>
>>> The read-only attribute is a "Windows" thing. Cygwin's utilities focus=
on
>>> supporting POSIXy/Linuxy ways of doing things. You can't expect Cygwin=
's
>>> tools to manage all of Window's permission facilities in the same way as
>>> Windows does. The read-only flag is one case where you'll see a diverg=
ence.
>>> If you need that flag set, you'll need your own wrapper to set it based=
on
>>> the POSIX (or ACL) permissions. The read-only attribute really is quite
>>> anachronistic though IMO. It conflicts with the more powerful ACLs. If
>>> you have the option, it's better not to use that flag.
>>
>> IMO the behaviour is inconsistent if the flag is used/interpreted on one=
(the
>> read) operation but NOT being written/changed on the other (write) opera=
tion.
>> My approach would be either drop it completely or support it on both ends
>> (the preferred option).
>
>Actually, the read-only attribute is not used by Cygwin to determine POSIX
>permissions.
According to what I have seen, the command=20
attrib +R wp.txt
changes ONLY the read-only flag - when I look at the Security page of the f=
ile properties dialog in Windows Explorer, the ACLs are not modified by att=
rib. Still Cygwin would see the file as read-only after the attrib call (pl=
ease see my original post for the complete sequence of commands).
>> By the looks of it (see
>> http://sourceware.org/ml/cygwin/2002-05/msg00317.html), this problem has
>> been addressed and potentially solved before, so I wonder if something is
>> broken here.
>
>No, nothing is broken. Things have changed since 2002. If you want the g=
ory
>details, you can look in the email archives. The short of it is, making
>read-only, Windows ACLs, and POSIX permissions all agree is overly
>complicated. So we've dropped read-only support now.
But AFAIK (see above) only for write operations.
I also agree that there is a complicating overlap between the read-only att=
ribute and the ACLs. Nevertheless, most Windows programs honour the read-on=
ly flag and Explorer can display a column listing such attributes as oppose=
d to effective ACL permissions.=20
The Samba server struggles with similar problems, as it also has to transla=
te between POSIX and Windows permissions. Samba's solution is to emulate AC=
Ls AND the read-only flag. It would be interesting how Samba treats changes=
to the read-only flag done by Windows, how it translates them to Linux per=
missions and back to Windows (does it change ACLs as well?). When I've got =
some time, I'll look into this.
>> The background to all this is that I am using RCS (I know, almost as
>> anachronistic as the read-only attribute, but that's dictated by my
>> workplace) under both Windows and Linux and RCS relies heavily on the
>> read-only attribute of files to be correct. IMO, it wouldn't hurt if the
>> Cygwin tools would write the Windows read-only attribute when they creat=
e a
>> Cygwin read-only file?
>
>Cygwin has a package for RCS. Perhaps that could solve your problem?
Thanks for pointing that out, I will have a look at that as well.
Regards,
Christian
--
Problem reports: http://cygwin.com/problems.html
FAQ: http://cygwin.com/faq/
Documentation: http://cygwin.com/docs.html
Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
- Raw text -