Re: [PATCH 0/4][RFC] NFSv3: implement extended attribute (XATTR) protocol

[Christoph Hellwig <hch@infradead.org>]

On Tue, Sep 22, 2009 at 11:03:25PM +1000, James Morris wrote:
> On Tue, 22 Sep 2009, Christoph Hellwig wrote:
> 
> > Note that the mapping should be really simple.  Both the NFS protocol
> > and XFS implement the same IRIX-xattr format that has a numerical
> > namespace instead of the string prefix Linux has.  If you just use the
> > same mapping as XFS it should not have interoperability problems.
> 
> One issue may be that the IRIX protcol for listxattr includes a 
> "attrlist_cursor_kern_t cursor" -- presumably to allow the client to index 
> into large lists of xattrs.  I'm going to guess that this doesn't happen 
> much in practice, although to have interop with IRIX, we'd need to handle 
> this in some useful way.

Yeah, unfortunately XFS experts those semantics via the horrible list
attrs by handle ioctls and carries a lot of cruft around to allow using
the cursor and validating the btree tate stored in it.  It's a real
mess.

Personally I'd just kill it and do a similar indexing scheme that
libattr uses to emulate the IRIX API (libattr/libattr.c:attr_list() in
the libattr repository)