Re: [PATCH 4/6] mkfs: fix hardlink detection in directory import code

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

On Tue, Jun 30, 2026 at 07:38:52AM +0200, Christoph Hellwig wrote:
> On Mon, Jun 29, 2026 at 06:03:41PM -0700, Darrick J. Wong wrote:
> > From: Darrick J. Wong <djwong@kernel.org>
> > 
> > There's a serious problem in the hardlink detection code in the new mkfs
> > protofile functionality that copies a directory tree into the new
> > filesystem.  It's been long established that hardlinks can only be
> > detected by comparing st_ino *and* st_dev, but the new code doesn't do
> > that.
> 
> Yes.
> 
> > Fix the detector, and stop passing struct stat objects by
> > value(!) since they are quite large.
> 
> Without looking at the code I suspect the compiler silently passes
> them by references as long as the functions are static, but it's
> still good to fix this up.
> 
> >  static void
> >  writetimestamps(
> >  	struct xfs_inode	*ip,
> > -	struct stat		*statbuf)
> > +	const struct stat	*statbuf)
> 
> It also seems to constify a few things :)

Yeah, I'll modify the commit message to state that we pass around const
statbuf pointers because none of the protofile code needs to modify them
once we've sampled the open fd.

> > -	hardlink_tracker.entries[hardlink_tracker.count].src_ino = src_ino;
> > +	hardlink_tracker.entries[hardlink_tracker.count].src_dev = filestat->st_dev;
> > +	hardlink_tracker.entries[hardlink_tracker.count].src_ino = filestat->st_ino;
> >  	hardlink_tracker.entries[hardlink_tracker.count].dst_ino = dst_ino;
> 
> A bunch of overly long lines.  This would probably benefit from
> a local variable for the tracker entry.

and add a convenience variable here to reduce the long lines.

> Otherwise looks good, although I would have split it into a few patches.

<nod> I'll go fix the statbuf pointers separately then.

--D