Re: [PATCH 21/21] hfsplus: remove can_set_xattr

From: Vyacheslav Dubeyko <slava@dubeyko.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 21/21] hfsplus: remove can_set_xattr
Date: Thu, 26 Dec 2013 14:15:49 +0400	[thread overview]
Message-ID: <1388052949.4168.91.camel@slavad-ubuntu> (raw)
In-Reply-To: <20131226094853.GA27078@infradead.org>

On Thu, 2013-12-26 at 01:48 -0800, Christoph Hellwig wrote:
> On Tue, Dec 24, 2013 at 10:41:44AM +0400, Vyacheslav Dubeyko wrote:
> > > -
> > > -	if (strncmp(name, XATTR_MAC_OSX_PREFIX,
> > > -				XATTR_MAC_OSX_PREFIX_LEN) == 0)
> > > -		name += XATTR_MAC_OSX_PREFIX_LEN;
> > 
> > Removing this skipping of virtual "osx." prefix means that you save it
> > on volume. But such action means volume corruption really. Because HFS+
> > volume hasn't such prefixes for xattrs in AttributesFile. Usually,
> > special xattrs has prefix "com.apple.*" but others haven't any prefix
> > and can be named as you want. So, I think that it is not correct
> > modification.
> 
> With my patch applied we don't add the prefix that later gets stripped
> in the first place:
> 
>  - hfsplus_osx_setxattr gets called without the prefix from the VFS code
>  - the code to add the prefix in hfsplus_osx_setxattr is removed by the
>    patch
>  - the code to remove it again in __hfsplus_setxattr is removed as well
> 
> Because of the way the handlers work no other caller of
> __hfsplus_setxattr should ever have a name with the osx prefix.
> 
> Same for the getxattr side.

I feel some confusion. :) As far as I can see, generic handlers are
connected with a prefix:

const struct xattr_handler hfsplus_xattr_osx_handler = {
        .prefix = XATTR_MAC_OSX_PREFIX,
        .list   = hfsplus_osx_listxattr,
        .get    = hfsplus_osx_getxattr,
        .set    = hfsplus_osx_setxattr,
};

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?

With the best regards,
Vyacheslav Dubeyko.