Re: [PATCH 6/6] xfs: check di_forkoff correctly in scrub

["Darrick J. Wong" <djwong@kernel.org>]

On Fri, Sep 11, 2026 at 05:07:45PM +0200, Christoph Hellwig wrote:
> On Thu, Sep 10, 2026 at 10:54:58PM -0700, Darrick J. Wong wrote:
> > The di_forkoff check in xchk_dinode is incorrect, according to LOLLM.
> > XFS_DFORK_BOFF returns a byte count relative to the start of the literal
> > area, not the start of the inode.  Therefore, this check won't flag
> > di_forkoff values that are larger than the literal area but not the
> > inode size itself.  Fix this check; sadly the old APTR code was correct.
> 
> The fi looks good, but I really which we could encapsulate this
> magic >> 3 a bit better (here and elsewhere).

I /did/ think about adding a cleanup to do:

#define XFS_B_TO_FORKOFF(b)	((b) >> 3)
#define XFS_FORKOFF_TO_B(f)	((f) << 3)

and then code like this:

fs/xfs/libxfs/xfs_attr_leaf.c:782:      minforkoff = max_t(int64_t, dsize, xfs_bmdr_space_calc(MINDBTPTRS));
fs/xfs/libxfs/xfs_attr_leaf.c:783:      minforkoff = roundup(minforkoff, 8) >> 3;
fs/xfs/libxfs/xfs_attr_leaf.c:786:      maxforkoff = XFS_LITINO(mp) - xfs_bmdr_space_calc(MINABTPTRS);
fs/xfs/libxfs/xfs_attr_leaf.c:787:      maxforkoff = maxforkoff >> 3;   /* rounded down */

becomes:

	minforkoff = XFS_B_TO_FORKOFF(max_t(int64_t, dsize,
				xfs_bmdr_space_calc(MINDBTPTRS)));
	maxforkoff = XFS_B_TO_FORKOFF(XFS_LITINO(mp) -
				xfs_bmdr_space_calc(MINABTPTRS));

There aren't as many users of FORKOFF_TO_B though:

static inline unsigned int xfs_inode_fork_boff(struct xfs_inode *ip)
{
	return XFS_FORKOFF_TO_B(ip->i_forkoff);
}

> Reviewed-by: Christoph Hellwig <hch@lst.de>

Thanks!

--D