Re: [PATCH 27/32] xfs: Add parent pointer ioctls

Christoph Hellwig
2024-04-16T19:01:53Z

On Tue, Apr 16, 2024 at 11:52:09AM -0700, Darrick J. Wong wrote:
> > > <nod> But does exportfs actually want parent info for a nondirectory?
> > > There aren't any stubs or XXX/FIXME comments, and I've never heard any
> > > calls (at least on fsdevel) for that functionality.
> >
> > It doesn't. It would avoid having disconnected dentries, but
> > disconnected non-directory dentries aren't really a problem.
>
> For directories, I think the dotdot lookup is much cheaper than scanning
> the attrs to find the first nongarbage XFS_ATTR_PARENT entry.

It is.

But I was confused again, it's been a while since I worked on that code..

We do the full reconnection for non-directories if NFSD asks for it (the
XFS or VFS handle code won't hit this because our acceptable callback
always returns true). That code does a readdir on the parent and
returns the name when it finds the inode number. For files without
crazy number of hardlinks just looking over the parent pointers would
be a lot more efficient for that.