patch draft for extended attributes on linux

jw schultz jw at
Thu Jun 26 15:01:08 EST 2003

On Thu, Jun 26, 2003 at 02:51:19PM +1000, Martin Pool wrote:
> On 25 Jun 2003, Wayne Davison <wayned at> wrote:
> > On Wed, Jun 25, 2003 at 10:34:38AM +1000, Martin Pool wrote:
> > > There is no mtime for xattrs, so they are transferred every time as
> > > part of the file list.
> > 
> > One possibly better solution would be to create some kind of CRC of the
> > xattr data (MD4/MD5/whatever) and send just that in the file list for
> > each file.  This would allow you to figure out when to update the xattr
> > data, but the protocol would need to be modified to send the xattr data
> > during the file-update phase (and possibly to allow the reciever to
> > request just an xattr update without doing a file update).
> That's a pretty good idea.  For the moment I just wanted a minimal
> patch, as traffic size is not an overwhelming consideration for the
> particular user I was helping.
> However, for many realistic cases the xas are quite small.  It is
> entirely possible for a file's attr and value them to be smaller than
> a 20-byte SHA1.  (Well, perhaps not with my inefficient packing, but
> in principle they might be.)
> In cases where xattrs are used for security information, it might not
> be sufficient to apply them just at the end of the transfer.  That
> might make the permissions on the temporary file too weak.  Or perhaps
> not -- I just didn't want to think about it. :-)

I'd say that a security regimen that requires xattrs to
tighten security is misguided.

	J.W. Schultz            Pegasystems Technologies
	email address:		jw at

		Remember Cernan and Schmitt

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