patch draft for extended attributes on linux

Martin Pool mbp at
Thu Jun 26 14:51:19 EST 2003

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. :-)


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