Re: [PATCH] xfs: move the define for superblock magic to uapi

[Dave Chinner <david@fromorbit.com>]

On Fri, Oct 05, 2018 at 11:23:56AM -0700, Darrick J. Wong wrote:
> On Fri, Oct 05, 2018 at 08:10:32PM +0200, Adam Borowski wrote:
> > On Fri, Oct 05, 2018 at 09:06:00AM -0700, Darrick J. Wong wrote:
> > > On Fri, Oct 05, 2018 at 02:27:41PM +0200, Adam Borowski wrote:
> > > > Needed by users of fstatfs().
> > > 
> > > NAK.
> > > 
> > > The XFS superblock magic number is part of the on-disk format definition
> > > of XFS. It belongs with all the other on-disk format definitions in this
> > > file.
> > > 
> > > I don't think it's a good idea for userspace to associate s_magic with
> > > userspace API feature sets, though the cat's long escaped the bag on
> > > that one.
> > > 
> > > With that being reality, "the XFS superblock magic number" has a
> > > different semantic meaning than "the agreed upon statfs.f_type value for
> > > XFS", which means the latter should have a different symbol name to
> > > reflect that difference.
> > 
> > Ie, you'd be ok with the same value to be defined in two places -- do I
> > understand this right?
> > 
> > > > --- a/fs/xfs/libxfs/xfs_format.h
> > > > -#define	XFS_SB_MAGIC		0x58465342	/* 'XFSB' */
> > > > +#define	XFS_SB_MAGIC		XFS_SUPER_MAGIC /* 0x58465342 = 'XFSB' */
> > > > --- a/include/uapi/linux/magic.h
> > > >  #define JFFS2_SUPER_MAGIC	0x72b6
> > > > +#define XFS_SUPER_MAGIC		0x58465342	/* "XFSB" */
> > > >  #define PSTOREFS_MAGIC		0x6165676C
> 
> Sorry, hit send too fast.
> 
> include/uapi/linux/magic.h would get:
> 
> #define XFS_STATFS_MAGIC	0x58465342	/* 'XFSB' */

$ man statfs |grep 0x5846
           XFS_SUPER_MAGIC       0x58465342
$

-Dave.
-- 
Dave Chinner
david@fromorbit.com