Accessing .zfs/snapshot using NFS fails

[cohdavid]

When I try to access a snapshot directory on a ZFS filesystem shared using NFS it fails, and I see error messages like this using dmesg:

NFS: directory .zfs/snapshot contains a readdir loop.Please contact your server vendor. The file: snap6 has duplicate cookie 522777912

It makes no difference if I use NFSv3 or NFSv4, and when I try a small readdir loop, the last entry is repeated. The system is running Debian Wheezy amd64, using the 0.6.3-1~wheezy version of your Debian ZFS packages.

The following shell script triggers the bug:

! /bin/bash

zfs create tank/share
zfs set [email protected]/32 tank/share
zfs share tank/share

for i in $(seq 1 10); do
dd if=/dev/zero of=/tank/share/$i bs=4k count=1k
zfs snapshot tank/share@snap$i
done

mount 127.0.0.1:/tank/share /mnt -t nfs4
perl -e 'opendir DIR, "/mnt/.zfs/snapshot/";while(readdir DIR){print"$_\n"};'

umount /mnt
mount 127.0.0.1:/tank/share /mnt -t nfs -o vers=3
perl -e 'opendir DIR, "/mnt/.zfs/snapshot/";while(readdir DIR){print"$_\n"};'

[behlendorf]

This is not yet supported under Linux. There is an initial patch out there which adds support but it still needs to be reviewed and merged.

Thank for you filing this, but I'm closing this a duplicate of #1655 and #616.