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(-) -- 2.26.2
