From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH 21/21] hfsplus: remove can_set_xattr
Date: Thu, 26 Dec 2013 02:45:32 -0800
Message-ID: <20131226104532.GA11456@infradead.org>
References: <20131220131635.650823732@bombadil.infradead.org>
 <20131220132524.900291394@bombadil.infradead.org>
 <636E01BC-12FD-452B-8B1C-320B6EADAEFD@dubeyko.com>
 <20131222192818.GA32565@infradead.org>
 <1387780809.3991.21.camel@slavad-ubuntu>
 <20131223143706.GA8235@infradead.org>
 <1387867304.3974.21.camel@slavad-ubuntu>
 <20131226094853.GA27078@infradead.org>
 <1388052949.4168.91.camel@slavad-ubuntu>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: Christoph Hellwig <hch@infradead.org>, viro@zeniv.linux.org.uk,
	linux-fsdevel@vger.kernel.org
To: Vyacheslav Dubeyko <slava@dubeyko.com>
Return-path: <linux-fsdevel-owner@vger.kernel.org>
Received: from bombadil.infradead.org ([198.137.202.9]:44285 "EHLO
	bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751831Ab3LZKpf (ORCPT
	<rfc822;linux-fsdevel@vger.kernel.org>);
	Thu, 26 Dec 2013 05:45:35 -0500
Content-Disposition: inline
In-Reply-To: <1388052949.4168.91.camel@slavad-ubuntu>
Sender: linux-fsdevel-owner@vger.kernel.org
List-ID: <linux-fsdevel.vger.kernel.org>

On Thu, Dec 26, 2013 at 02:15:49PM +0400, Vyacheslav Dubeyko wrote:
> So, if we don't add the "osx." prefix on the fly then it means that we
> don't call proper handler. HFS+ doesn't keep "osx." prefix on the volume
> because this prefix is Linux way only to process xattrs. For example, I
> can create xattr with name "test" under Mac OS X. And this xattr's name
> hasn't "osx." prefix. Can I access to this xattr under Linux if we don't
> add "osx." prefix on the fly?
> 
> Maybe I misunderstand some part of your patch set?

Most filesystems don't store the prefix on disk, but instead a binary
namespace, that's why the handler code strips it (although we might want
to eventually add a flag to not strip it given that we have a few
filesystems storing it now).

So let's look at the case of a fgetxattr(fd, "osx.foo", ...) with the old
and my new code.

Old:

 \---		sys_fgetxattr(fd, "osx.foo", ....
  \			...
   \---		generic_getxattr(dentry, "osx.foo", ...
    \			[xattr_resolve_name strips the prefix]
     \---	hfsplus_osx_getxattr(dentry, "foo", ...
      \			[adds back prefix]
       \		...
        \---	__hfsplus_getxattr(dentry, "osx.foo", ...
	 \		[strips the prefix again]
	  \---	hfsplus_find_attr(sb, ino, "foo", ...


New:

 \---		sys_fgetxattr(fd, "osx.foo", ....
  \			...
   \---		generic_getxattr(dentry, "osx.foo", ...
    \			[xattr_resolve_name strips the prefix]
     \---	hfsplus_osx_getxattr(dentry, "foo", ...
      \			...
       \---	__hfsplus_getxattr(dentry, "foo", ...
        \---	hfsplus_find_attr(sb, ino, "foo", ...