zfs mount is not namespace aware

[akorn]

Hi,

I'm trying to use zfsonlinux with linux-vserver, which makes heavy use of namespaces (mount, ipc etc.).

zfs seems to lack namespace support entirely.

root@jayhawk / # mountpoint /srv
/srv is a mountpoint
root@jayhawk / # vnamespace -i 0 -e 78 -- /bin/zsh
# We're in a different mount namespace now:
root@jayhawk / # mountpoint /srv
/srv is not a mountpoint
root@jayhawk / # zfs mount tank/srv
cannot mount 'tank/srv': filesystem already mounted
root@jayhawk / # grep 'tank/srv /' /proc/mounts
root@jayhawk / #

"zfs mount tank/srv" should have succeeded, because tank/srv is only mounted in the default namespace, but not this one.

Andras

[akorn]

The issue goes deeper (which, in retrospect, is kind of obvious): when a namespace is created as a copy of the host namespace, and a zfs dataset is unmounted there, it becomes unmounted in the host namespace too.

[akorn]

Actually, this latter problem may have had to do with me using mount --make-shared on the affected tree. I'll try to confirm this later.

[akorn]

Yes, the phantom umounting was caused by mount --make-shared. So the only problem with zfsonlinux seems to be that zfs mount(/unmount?) doesn't work correctly inside alternative mount namespaces.

[ryao]

This would require doing #434 first. Then some of the code for making ZFS work in Solaris Zones could probably be used here.

[behlendorf]

This should work in the current code, alternate namespaces are now supported.