[Bug 696435] Re: wait-for-root fails to detect nbd root

[Joseph Salisbury]

** Tags added: kernel-da-key

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Title:
  wait-for-root fails to detect nbd root

Status in linux package in Ubuntu:
  Fix Released
Status in nbd package in Ubuntu:
  Invalid
Status in systemd package in Ubuntu:
  Fix Released
Status in linux source package in Xenial:
  In Progress
Status in systemd source package in Xenial:
  Incomplete

Bug description:
  When using an nbd root, wait-for-root blocks for 30 seconds before
  booting continues successfully.

  Using Ubuntu Natty, related packages versions:
      nbd-client 1:2.9.16-6ubuntu1 
      initramfs-tools 0.98.1ubuntu9

  The wait-for-root call from /usr/share/initramfs-tools/scripts/local:
  	while [ -z "${FSTYPE}" ]; do
  		FSTYPE=$(wait-for-root "${ROOT}" ${ROOTDELAY:-30})

  		# Run failure hooks, hoping one of them can fix up the system
  		# and we can restart the wait loop.  If they all fail, abort
  		# and move on to the panic handler and shell.
  		if [ -z "${FSTYPE}" ] && ! try_failure_hooks; then
  			break
  		fi
  	done

  I replaced wait-for-root with a sh script that did `set >&2`, here are the relevant environment variables at the time wait-for-root was called:
  ROOT='/dev/nbd0'
  ROOTDELAY=''
  ROOTFLAGS=''
  ROOTFSTYPE=''
  nbdroot='192.168.0.1,2011'

  It's probably worth noting that "nbd0: unknown partition table" was
  displayed asynchronously 1-2 seconds after wait-for-root was invoked
  and while it was still waiting. But I tried adding a "sleep 5" as the
  last line of local-top/nbd, so that the nbd message was displayed a
  lot before wait-for-root was called, and it didn't make a difference.
  So I don't think a race condition is involved in this problem.

  Temporarily I'm passing rootdelay=1 in the kernel command line to work
  around the problem.

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