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Date: Mon, 2 Nov 2009 15:02:21 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Huang Ying <ying.huang@intel.com>
Cc: Joe Perches <joe@perches.com>, Steven Whitehouse <swhiteho@redhat.com>,
       Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [RFC 2/2] Use unified UUID/GUID definition in gfs2
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On Mon, 02 Nov 2009 08:59:43 +0800
Huang Ying <ying.huang@intel.com> wrote:

> On Mon, 2009-11-02 at 01:35 +0800, Andrew Morton wrote: 
> > On Wed, 14 Oct 2009 14:30:07 +0800 Huang Ying <ying.huang@intel.com> wrote:
> > 
> > > Replace u8[16] UUID definition in gfs2.
> > > 
> > > Signed-off-by: Huang Ying <ying.huang@intel.com>
> > > ---
> > >  fs/gfs2/incore.h            |    3 ++-
> > >  fs/gfs2/ops_fstype.c        |    2 +-
> > >  fs/gfs2/sys.c               |   14 ++++----------
> > >  include/linux/gfs2_ondisk.h |    3 ++-
> > >  4 files changed, 9 insertions(+), 13 deletions(-)
> > > 
> > > --- a/fs/gfs2/incore.h
> > > +++ b/fs/gfs2/incore.h
> > > @@ -15,6 +15,7 @@
> > >  #include <linux/slow-work.h>
> > >  #include <linux/dlm.h>
> > >  #include <linux/buffer_head.h>
> > > +#include <linux/uuid.h>
> > >  
> > >  #define DIO_WAIT	0x00000010
> > >  #define DIO_METADATA	0x00000020
> > > @@ -483,7 +484,7 @@ struct gfs2_sb_host {
> > >  
> > >  	char sb_lockproto[GFS2_LOCKNAME_LEN];
> > >  	char sb_locktable[GFS2_LOCKNAME_LEN];
> > > -	u8 sb_uuid[16];
> > > +	uuid_be sb_uuid;
> > >  };
> > >  
> > 
> > Breaks `make headers_check':
> > 
> > include/linux/gfs2_ondisk.h:14: included file 'linux/uuid.h' is not exported
> > 
> > I don't think we want to export linux/uuid.h to userspace.  But
> > fs/gfs2/incore.h _is_ shared with userspace, and needs linux/uuid.h.
> 
> When writing uuid.h, I think it should be exported to userspace. Why
> should we not export it to user space?

It contains a pile of stuff which is of no use to userspace - functions
definitions, function declarations, macros, additional linux includes.

If we're going to do this then we need a separate header file which
contains the userspace-needed things.  And we'd need to check that it's
desirable to use __u8 in userspace headers.

And we'll need to wake Steven up to actually take a look at the patches!