From: David Vallner <david@...>
Date: 2006-02-08T05:52:30+09:00
Subject: Re: How to check NTFS file permissions?

Dňa Utorok 07 Február 2006 20:49 Chris napísal:
> This problem comes up because WinXP keeps putting it's 'System Volume
> Information' directories on each partition.  In this case, I think the FS
> was created by an earlier incarnation of the machine I'm on.
>
> However it is marked Read Only, and there doesn't seem to be any way to
> change it.  Properties window says it is Read only (with a square, not a
> checkmark) and Hidden, and it lets me think I'm changing it, even asks if
> I want to change all subordinates, but never changes it.  That's an OT,
> but I'd be happy to hear a solution to it.

The Properties window doesn't display whether a directory is or is not 
readable as per the POSIX-y meaning of the concept. It should technically 
display as read-only, if the contents of the directory are read-only, but the 
contents aren't actually checked, if only because it might end up taking 
bloody long. I'm not even sure how those vestigial FAT attributes map to NTFS 
ones. If you really want to get nitty-gritty with the system, check whatever 
setting it is that's hiding the NTFS ACLs from you and look at those.

Slight sidenote: You really don't want to touch System Volume Information 
unless you really know what you're doing.

>
> The problem I'm having is that File.readable? and File.executable? both
> give me true for that directory, but if I try Dir.chdir into it, it throws
> an exception.
>
> Is there a check I can do, or is my only option: rescue Errno::EACCES?
> And I guess the followup is: is it much more expensive in Ruby to catch
> exceptions than to execute regular code (as it is in Java)?
>

Do you expect to run into inaccessible directories in the script more often 
than you actually process data in accessible ones? Unless so, I say don't 
bother and use Errno::EACCES. The overhead isn't likely to be significant 
compared to total execution time.

David Vallner