If you're running zfs tools in a container setting the timeout to 0 will
likely be helpful. The device node will never appear in the containers /dev
since a) it's a tmpfs and b) even if it were a devtmpfs it wouldn't help
since devtmpfs isn't namespaced. (In fact udevd will even ignore any device
event inside an unprivileged container since it's sent with
INVALID_{G,U}ID. I have kernel patches to handle this and a bunch of other
quirks that are up for merging.) For unpriv containers any device that you
somehow create by talking to /dev/zfs (e.g. by having LXD create a device
node for the container) will never show up in the container. It will always
show up in the hosts devtmpfs.

On the host setting it to 0 should also not have a negative effect since
the modprobe should a) cause devtmpfs to create the device node *before*
sending a uevent and b) zfs userspace will likely wait for udevd to settle
aka setup symlinks and persistent device naming. The timeout logic only
makes sense for old udevd implementations that do create device nodes and
might do so in a delayed manner. But better to test.

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You received this bug notification because you are a member of Kernel
Packages, which is subscribed to zfs-linux in Ubuntu.
https://bugs.launchpad.net/bugs/1760173

Title:
  zfs, zpool commands hangs for 10 seconds without a /dev/zfs

Status in lxd package in Ubuntu:
  New
Status in zfs-linux package in Ubuntu:
  Triaged

Bug description:
  1. # lsb_release -rd
  Description:  Ubuntu 16.04.4 LTS
  Release:      16.04

  2. # apt-cache policy zfsutils-linux
  zfsutils-linux:
    Installed: 0.6.5.6-0ubuntu19
    Candidate: 0.6.5.6-0ubuntu19
    Version table:
   *** 0.6.5.6-0ubuntu19 500
          500 http://archive.ubuntu.com/ubuntu xenial-updates/main amd64 
Packages
          100 /var/lib/dpkg/status

  3. When inside a lxd container with zfs storage, zfs list or zpool
  status either return or report what's going on.

  4. When inside a lxd container with zfs storage, zfs list or zpool
  status appears to hang, no output for 10 seconds.

  strace reveals that without a /dev/zfs the tools wait for it to appear
  for 10 seconds but do not provide a command line switch to disable or
  make it more verbose.

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: zfsutils-linux 0.6.5.6-0ubuntu19
  ProcVersionSignature: Ubuntu 4.13.0-36.40~16.04.1-generic 4.13.13
  Uname: Linux 4.13.0-36-generic x86_64
  ApportVersion: 2.20.1-0ubuntu2.15
  Architecture: amd64
  Date: Fri Mar 30 18:09:29 2018
  ProcEnviron:
   TERM=xterm-256color
   PATH=(custom, no user)
   LANG=C.UTF-8
  SourcePackage: zfs-linux
  UpgradeStatus: No upgrade log present (probably fresh install)

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