patch draft for extended attributes on linux

jw schultz jw at
Thu Jun 26 21:15:08 EST 2003

On Thu, Jun 26, 2003 at 10:50:29AM +0100, Max Bowsher wrote:
> 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 the case of xattrs-as-acls, it is quite likely that the same acl will be
> applied to many different files. It might therefore be worth considering a
> table-based approach: "File foo has acl has attribute number 3", where the
> attribute numbers refer to a table constructed at file-list generation time.

Thanks Max.  I think this is just a get over the hump
solution at the moment.

My thought with regards to the ACLs and even XAs given their
high rate of sameness was to transmit their checksums with
the flist and build a hash table of those on the receiver.
That way we only would request each value once.

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

		Remember Cernan and Schmitt

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