[PATCH 5/8] xfs: implement iomap based buffered write path

[Christoph Hellwig]

On Thu, Apr 14, 2016 at 08:58:14AM -0400, Brian Foster wrote:
> > +static int
> > +xfs_file_iomap_end_delalloc(
> > +	struct xfs_inode	*ip,
> > +	loff_t			offset,
> > +	loff_t			length,
> > +	ssize_t			written)
> > +{
> > +	struct xfs_mount	*mp = ip->i_mount;
> > +	xfs_fileoff_t		start_fsb;
> > +	xfs_fileoff_t		end_fsb;
> > +	int			error = 0;
> > +
> > +	start_fsb = XFS_B_TO_FSB(mp, offset + written);
> > +	end_fsb = XFS_B_TO_FSB(mp, offset + length - written);
> > +
> 
> Just skimming over this series... but shouldn't this be offset + length?
> Why walk back from the end of the allocated range?

Because the interface from the core iomap code need to pass the
length of the actually mapped range, and the amount of bytes successfully
written into it to the filesystem, as other filesystems will require
this for their locking.  We need to convert it back at some point,
and it seems more logical here than in the caller.