patch draft for extended attributes on linux

Max Bowsher maxb at
Thu Jun 26 19:50:29 EST 2003

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.


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