Re: [Bug-tar] RFE? tar doesn't copy file attributes or ACL's (full permissions)

[Andreas Dilger]

On Aug 02, 2009  12:41 -0700, Linda A. Walsh wrote:
> Would it be possible to get tar to copy (or ignore) file attributes, and 
> to copy ACL's if they exist ( maybe via an option)?
>
> Some attr's I really like to keep on files, and end up having to use  
> something a host of different utils (depending on fs and os), but
> common examples are the '+d" 'don't dump' attribute -- something I
> usually set on large multi-gig scratch files I'm using for testing,
> or temporary copies of DVD's on my disk (certainly don't need to back
> up such things as the original is the DVD -- much better than trying
> to use backup space).

This kind of file attribute (nodump, immutable, append-only, etc) isn't
backed up by tar yet, not even the ones that already back up extended
attributes (e.g. recent RHEL/FC tar with xattr patches).

> ACL's -- those would be most useful for me under Cygin-Windows.  Cygwin
> uses Windows ACL's itself for emulating the standard unix rwx permisions
> for groups, but native ACL's are also set for existing files that it 
> would be nice if they could be kept in a backup. (Since Window's
> native backup seems to die about 165G into its backup attempt (I think
> it is actually 'finished', and dies during final 'housekeeping').

ACLs are backed up by the patched RHEL/FC tar programs.

> I'd rather save it in a standard format if I could (i.e. tar)...
>
> Of course on Win, it has underlying file attribs as well, (HSRA...)

It might be possible that DOS/FAT/NTFS already have extensions to
backup/restore these attributes via tar, in which case they should
be extended to handle extN/xfs/jfs/btrfs/reiserfs attributes (which
are implemented with a common getattr() interface).

> Dunno how possible...but certainly the ext2+xfs 'd' attribs
> and file ACLS's -- it'd be up to the support libraries to actually
> be available to be able to pull the values in so 'tar' could store
> them.  
>
> _Maybe_ for Backwards compat such info could be stored ahead of a file
> in some variation of the filename?  Like if fn="filename", then store 
> attribs in .filename#.%attrib%.<hex-numbered ext>, if need to avoid fn 
> collisions?  

Probably the easiest way to back these attributes up would be to store
them in a "virtual" extended attribute in a very simple (text?) encoding.
One possibility is like:

attributes=nodump,immutable

and if such an xattr is seen during file restore it is converted to the
apropriate bitfields and set via setattr().

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.