Re: [PATCH 3/3] xfs: make struct xfs_buf_log_format have a consistent size

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Thu, Jan 09, 2020 at 08:51:20AM +1100, Dave Chinner wrote:
> On Tue, Jan 07, 2020 at 08:18:25PM -0800, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@oracle.com>
> > 
> > Increase XFS_BLF_DATAMAP_SIZE by 1 to fill in the implied padding at the
> > end of struct xfs_buf_log_format.  This makes the size consistent so
> > that we can check it in xfs_ondisk.h, and will be needed once we start
> > logging attribute values.
> > 
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > ---
> >  fs/xfs/libxfs/xfs_log_format.h |    9 +++++----
> >  fs/xfs/xfs_ondisk.h            |    1 +
> >  2 files changed, 6 insertions(+), 4 deletions(-)
> > 
> > 
> > diff --git a/fs/xfs/libxfs/xfs_log_format.h b/fs/xfs/libxfs/xfs_log_format.h
> > index 8ef31d71a9c7..5d8eb8978c33 100644
> > --- a/fs/xfs/libxfs/xfs_log_format.h
> > +++ b/fs/xfs/libxfs/xfs_log_format.h
> > @@ -462,11 +462,12 @@ static inline uint xfs_log_dinode_size(int version)
> >  #define	XFS_BLF_GDQUOT_BUF	(1<<4)
> >  
> >  /*
> > - * This is the structure used to lay out a buf log item in the
> > - * log.  The data map describes which 128 byte chunks of the buffer
> > - * have been logged.
> > + * This is the structure used to lay out a buf log item in the log.  The data
> > + * map describes which 128 byte chunks of the buffer have been logged.  Note
> > + * that XFS_BLF_DATAMAP_SIZE is an odd number so that the structure size will
> > + * be consistent between 32-bit and 64-bit platforms.
> >   */
> > -#define XFS_BLF_DATAMAP_SIZE	((XFS_MAX_BLOCKSIZE / XFS_BLF_CHUNK) / NBWORD)
> > +#define XFS_BLF_DATAMAP_SIZE	(1 + ((XFS_MAX_BLOCKSIZE / XFS_BLF_CHUNK) / NBWORD))
> 
> Shouldn't this do something like:
> 
> #define __XFS_BLF_DATAMAP_SIZE	((XFS_MAX_BLOCKSIZE / XFS_BLF_CHUNK) / NBWORD)
> #define XFS_BLF_DATAMAP_SIZE	(__XFS_BLF_DATAMAP_SIZE + (__XFS_BLF_DATAMAP_SIZE & 1))
> 
> or use an appropriate round up macro so that if we change the log
> chunk size or the max block size, it still evaluates correctly for
> all platforms?

Ok, works for me.

> /me has prototype patches around somewhere that change
> XFS_BLF_CHUNK...

I remember those...

--D

> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@fromorbit.com