On Wed, 2022-12-07 at 09:43 +0100, Richard Weinberger wrote: > Currently when re-exporting a NFS share the NFS cross mount feature does > not work [0]. > This patch series outlines an approach to address the problem. > > Crossing mounts does not work for two reasons: > > 1. As soon the NFS client (on the re-exporting server) sees a different > filesystem id, it installs an automount. That way the other filesystem > will be mounted automatically when someone enters the directory. > But the cross mount logic of KNFS does not know about automount. > This patch series addresses the problem and teach both KNFSD > and the exportfs logic of NFS to deal with automount. > > 2. When KNFSD detects crossing of a mount point, it asks rpc.mountd to install > a new export for the target mount point. Beside of authentication rpc.mountd > also has to find a filesystem id for the new export. Is the to be exported > filesystem a NFS share, rpc.mountd cannot derive a filesystem id from it and > refuses to export. In the logs you'll see errors such as: > > mountd: Cannot export /srv/nfs/vol0, possibly unsupported filesystem or fsid= required > > To deal with that I've changed rpc.mountd to use generate and store fsids [1]. > Since the kernel side of my changes did change for a long time I decided to > try upstreaming it first. > A 3rd iteration of my rpc.mountd will happen soon. > > [0] https://marc.info/?l=linux-nfs&m=161653016627277&w=2 > [1] https://lore.kernel.org/linux-nfs/20220217131531.2890-1-richard@xxxxxx/ > > Changes since v1: > https://lore.kernel.org/linux-nfs/20221117191151.14262-1-richard@xxxxxx/ > > - Use LOOKUP_AUTOMOUNT only when NFSEXP_CROSSMOUNT is set (Jeff Layton) > > Richard Weinberger (3): > NFSD: Teach nfsd_mountpoint() auto mounts > fs: namei: Allow follow_down() to uncover auto mounts > NFS: nfs_encode_fh: Remove S_AUTOMOUNT check > > fs/namei.c | 6 +++--- > fs/nfs/export.c | 2 +- > fs/nfsd/vfs.c | 8 ++++++-- > include/linux/namei.h | 2 +- > 4 files changed, 11 insertions(+), 7 deletions(-) > This set looks reasonable to me. Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
