Date: Tue, 21 Jun 2011 20:51:22 +0200 From: Paul Schenkeveld <freebsd@psconsult.nl> To: freebsd-jail@freebsd.org Subject: Re: Exposing a hierarchy of ZFS datasets inside multiple jails Message-ID: <20110621185122.GA13459@psconsult.nl> In-Reply-To: <BANLkTikrWYnBAnQsXZ535OdX5tVp9eOrNQ@mail.gmail.com> References: <BANLkTikrWYnBAnQsXZ535OdX5tVp9eOrNQ@mail.gmail.com>
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Hi, On Fri, Jun 17, 2011 at 02:46:59PM -0400, Lars Kellogg-Stedman wrote: > Hello all, > > Hi there, > > I am trying to expose a hierarchy of home directories to a number of > FreeBSD jails. The home directories are configured such that each is a > unique ZFS dataset. The jails are used for development work and hence > are created and destroyed on a regular basis. > > My first thought was simply to use nullfs to mount /home inside the > jail, but nullfs doesn't provide any way to access subordinate > filesystems. > > My second thought was to export the directories via NFS and then run > the automounter daemon (amd) inside each jail. This would have Just > Worked...if it were possible to perform NFS mounts inside a jail. But > it's not. > > My third thought was to run amd on the host and provision nullfs > mounts into the jails...but amd support for nullfs doesn't exist. > > My fourth thought was to go back to exporting the directories using > NFS, because of course amd works with NFS, right? Unfortunately, > rather than mounting a directory on the target mountpoint, amd likes > to mount things in a temporary location (/.amd_mnt/...) and then > create a symlink...which, of course, is useless inside the jail > environment.t > > So maybe you could use nullfs to expose a subdirectory of /.amd_mnt to > the jail? No! This brings us back to my first attempt, in which we > find that there is no way to access subordinate filesystems using > nullfs. > > And then my head exploded. > > Is there a good solution for what I'm trying to do? A bad solution > would be to run a script after booting the jail that would create > multiple nullfs mountpoints for all the home directories, but this is > pretty clunky -- it would need to be run periodically to take into > account new directories or removed directories. So basically I would > have to write a poorly designed automounter. > > There must be a better way. How are other folks solving this? > > It looks like there are discussions going back several years about > setting the VFCF_JAIL on NFS filesystems, but it these haven't > resulted in any changes to the released code. Is this the best way to > go? In theory, if I build a kernel under which NFS is jail friendly I > can go ahead and run amd inside the jail Probably not a good solution but to stir the pool of thoughts a bit... Nullfs mounts and NFS mounts operate on filesystems (or datasets) and do not include subordinates. Smbfs operates on directory (sub)trees so have /home and /home/user[123...] datasets outside the jails, run samba there with a share called [home] (not to be confused with the [homes] share that comes with smb.conf.sample) and mount this share using mount_smbfs inside every jail (from fstab.<jailname>). Just my $.02 Regards, Paul Schenkeveld
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