xattrs questions

Wayne Davison wayned at samba.org
Sat Apr 7 16:18:50 GMT 2007

On Sat, Apr 07, 2007 at 07:13:16AM -0400, Victor Shoup wrote:
> But: will it allow backup from a file system that supports xattrs, to  
> one that does not?

Not as currently envisioned.  It would not be hard to add some
compatibility code into lib/sysxattrs.c that would allow an alternate
storage method to be used via the regular xattr access functions.  For
instance, a DB access method could be configured into rsync that would
store records indexed by inode and xattr name.  However, I'm expecting
someone who wants to backup xattrs to supply a destination disk that
supports xattrs.

> Moreover, even if both machines support xattrs, their might be
> restrictions and subtle differences in semantics that could prevent
> one from directly  mapping an xattr on one machine to an xattr on
> another.

It's not expected that xattrs from one system type will be meaningful on
another, just stored.  There is already compatibility code in place that
makes sure that everyone is transmitting xattrs in a namespace, so Mac
xattrs get transmitted with a "user" namespace prefixed.  This allows
them to be backed up and restored between differing system types.  All
the implementations that I'm aware of allow arbitrary names in the user

Rsync doesn't do anything to try to work around size restrictions
between differing implementations (just like it doesn't try to work
around differing path-length limits), so it will be up to the user
to make sure that their copy is possible.

If you see any problems/concerns with this, please feel free to discuss
them.  It would be nice to get them handled sooner rather than later.


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