Re: [PATCH 00/14] Overlayfs NFS export support

[Jeff Layton <jlayton@kernel.org>]

On Thu, 2017-11-09 at 14:02 -0500, J . Bruce Fields wrote:
> On Tue, Oct 17, 2017 at 07:44:17PM +0300, Amir Goldstein wrote:
> > Miklos,
> > 
> > This series implements NFS export support [3] and is based on
> > two prep patch sets [1][2] posted earlier to overlayfs list.
> > NFS export is enabled for overlayfs mount with the 'verify_dir'
> > and 'index=all' mount options.
> > 
> > The current implementation will copy up and index directories when
> > directory file handles are encoded. Those extra copy ups could be
> > avoided in the future.
> > 
> > The current implementation does NOT support encoding connectable
> > non-dir file handles for all overlay path types, so overlayfs should
> > not be exported with the 'subtree_check' option.
> > I hope this is not a show stopper for merging NFS export support?
> 
> I'm not a big fan of subtree_check, and I'd be OK with filesystems
> opting out of support for it.
> 
> I'm not sure what to expect when you actually try to export overlayfs
> with subtree_check.  Does it fail on the export, or when clients first
> try to access it, and what kind of error do you get?
> 

As part of the NFS reexport series that I posted a couple of years ago,
there was a set of patches that would make exportfs return a (sensible)
error message when it tried to enable it on a filesystem that didn't
support it.

We could look at resurrecting that if there is interest in allowing
filesystems to opt out of subtree checking. It wasn't terribly complex,
IIRC.

> > You'll notice that the series start by implementing naiive support
> > for pure upper files export and later on, replaces the implementation
> > of some of the operations. This may seem strange, but I found it
> > convenient to progress slowly between testable mile stones and I find
> > the series easier to review this way. Let me know if you want me to
> > change the way that this series is organized to get rid of code that
> > is later removed.
> > 
> > To unit test overlayfs file handles, I enhanced xfstest open_by_handle
> > test utility to encode/decode directories and check several other cases
> > that were not covered by the original xfstest test. On my xfstests NFS
> > export branch [4], there are two generic tests and one overlayfs specific
> > test on the 'exportfs' group.
> > 
> > I also ran the NFSTest nfstest_posix group on an exported overlayfs
> > mount, but that test only creates pure upper files in overlay upper dir,
> > so it is not much of a stress to the implementation.
> 
> Might also be interesting to run some nfs tests in a loop while
> restarting the server?
> 
> --b.
> 
> > 
> > Amir.
> > 
> > [1] https://github.com/amir73il/linux/commits/ovl-verify-dir
> > [2] https://github.com/amir73il/linux/commits/ovl-index-all
> > [3] https://github.com/amir73il/linux/commits/ovl-nfs-export
> > [4] https://github.com/amir73il/xfstests/commits/ovl-nfs-export
> > 
> > Amir Goldstein (14):
> >   ovl: hash all overlay inodes for NFS export
> >   ovl: grab i_count reference of lower inode
> >   ovl: use d_splice_alias() in place of d_add() in lookup
> >   ovl: copy up of disconnected dentries
> >   ovl: encode/decode pure-upper non-connectable file handles
> >   ovl: encode pure-upper connectable file handles
> >   ovl: decode pure-upper connectable file handles
> >   ovl: encode/decode struct ovl_fh format file handles
> >   ovl: encode non-pure-upper non-connectable file handles
> >   ovl: obtain a non-pure-upper disconnected dentry
> >   ovl: decode non-pure-upper non-connectable file handles
> >   ovl: reconnect non-pure-upper dir file handles
> >   ovl: wire up NFS export support
> >   ovl: document NFS export
> > 
> >  Documentation/filesystems/overlayfs.txt |  61 +++++
> >  fs/overlayfs/Makefile                   |   3 +-
> >  fs/overlayfs/copy_up.c                  |  74 ++++--
> >  fs/overlayfs/export.c                   | 433 ++++++++++++++++++++++++++++++++
> >  fs/overlayfs/inode.c                    |  23 +-
> >  fs/overlayfs/namei.c                    |  96 ++++---
> >  fs/overlayfs/overlayfs.h                |  32 ++-
> >  fs/overlayfs/super.c                    |  25 ++
> >  fs/overlayfs/util.c                     |  13 +-
> >  9 files changed, 678 insertions(+), 82 deletions(-)
> >  create mode 100644 fs/overlayfs/export.c
> > 
> > -- 
> > 2.7.4

-- 
Jeff Layton <jlayton@kernel.org>