Re: [Ocfs2-devel] [PATCH 13/39] ocfs2: Add extended attribute support

Mark Fasheh
2008-10-09T00:38:35Z

On Wed, Oct 08, 2008 at 10:04:40PM +0800, Tao Ma wrote:
>
>
> Christoph Hellwig wrote:
> > On Wed, Oct 08, 2008 at 09:56:41AM +0800, Tiger Yang wrote:
> >> I have looked the patch for btrfs about this. We are different.
> >> Btrfs store the whole xattr name including the prefix "user."
> >> "trusted.", we store index number instead of it.
> >
> > I looked at the git tree and there are two users of
> > ocfs2_xattr_handler().
> >
> > (1) for using the ->list handler in listattr. That's something I fixed
> > in btrfs that I wanted to point you to. The whole concept of a
> > ->list handler is stupid, and it was only added as a hack for
> > the tmpfs "generic" xattr support which is a mess. Instead of
> > looking up a handler that would only do the same thing anyway
> > for all on-disk attributes just call the code directly and
> > have a map from index to prefix (look at
> > fs/xfs/linux-2.6/xfs_xattr.c for an example). You
> > also have a check for OCFS2_MOUNT_NOUSERXATTR for the user
> > attributes, but that's much easier done by just checking the
> > index in an if (and I'd personally just kill it completely, the
> > options doesn't seem useful - but that's an unrelated bit)
> yes, you are right. The handler for list is borrowed from ext3 and
> somewhat ugly. We just need the prefix name but use such a complicated
> method. Just a map from index to prefix should work fine.
> >
> > (2) For generating the hash. I don't quite understand why you want to
> > also hash the prefix if it's not store on disk anyway but sorted
> > into the numeric buckets.
> This is done intentionally. See the design doc
> http://oss.oracle.com/osswiki/OCFS2/DesignDocs/ExtendedAttributes.
> "Each entry has a 32-bit hash value associated with it. The hash value
> is calculated using the full (prefix.suffix) name of the xattr to avoid
> hash collisions when the same suffix is used in multiple attribute
> namespaces. "
> So Mark, do you think we need this prefix hash?
> Anyway, if we make consensus that the hash calculation doesn't need
> prefix any more, we can remove the ocfs2_xattr_handler safely.

Removing the prefix hash should be fine. Technically, this changes the disk
format, but nobody should be using this for production yet anyway.
--Mark

--
Mark Fasheh