[Bug 221512] Contents of ZFS datasets invisible after being mounted inside a jail with nullfs (Even after a reboot!)

bugzilla-noreply at freebsd.org bugzilla-noreply at freebsd.org
Mon Aug 14 12:06:20 UTC 2017


tsuroerusu at gmail.com changed:

           What    |Removed                     |Added
         Resolution|---                         |Not A Bug
             Status|New                         |Closed

--- Comment #1 from tsuroerusu at gmail.com ---
With a little bit of help, I managed to figure out what the problem was. It
turned out that I had run, head first, into the wall of nullfs not operating
across file systems. Thus inside the jail, the data was being saved to a
regular directory on my "storage/cloud"-dataset (Mountpoint: /storage/cloud),
whereas outside the jail the child file system "storage/cloud/bc", having been
left empty, was mounted over the folder "bc" on "storage/cloud", where the
files actually resided, thus "hiding" them from view outside the jail. A simple
"zfs unmount storage/cloud/bc" revealed them.

Anybody reading this in the future after a Google search: If you are using ZFS
and want to put a file system and all of its children into a jail then you
cannot use nullfs. Instead you need to either change the actual mount point
using "zfs set mountpoint=/jails/jail1/storage storage/path/to/filesystem" or
to attach the entire dataset to the jail, and allow it to be managed from
within the jail using "zfs jail".

I would like to propose that the man page for mount_nullfs contain a short
sentence about nullfs not crossing file system boundaries. From what I can tell
by, admittedly, giving it a quick look, I didn't see anything about that, so
it's possible that I simply missed it if it actually is in there.

I apologize for any inconvenience caused by this report.

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