Description of problem:
Current packaging of cloud-initramfs-tools only supports expansion of disk hosting "/" if "/" is hosted on a disk that is either wholly unpartitioned or is partitioned with standard (primary/logical/extended). Currently, there is no support for expansion of partitions containing an LVM-hosted "/".

Note: some security compliance suites (e.g., DISA STIGs) mandate the use of a specific minimum set of partitions implemented via LVM2. 

Version-Release number of selected component (if applicable):

dracut-modules-growroot version 0.20-2
cloud-utils-growpart version 0.27-10

Tested on RHEL 6.7 & 6.8 as well as CentOS 6.7 and 6.8 (hosted within AWS)

How reproducible:
Nothing to reproduce: it's in the package design

Steps to Reproduce:
1. Launch cloud instance with LVM-partitioned root filesystem - setting root disk size greater than template-size
2. Install dracut-modules-growroot
3. Reboot: 

Actual results:
When system comes back from reboot, partition hosting the root volume-group remains the same size

Expected results:
Partition containing the root volume group expands

Additional info:
A slight modification to the /usr/share/dracut/modules.d/50growroot/growroot.sh file to add logic for finding what partition hosts "/" will allow the final:

if out=$(growpart --update off "${rootdisk}" "${partnum}" 2>&1) ; then
                _info "${out}"

statement to function, correctly. As a quick-n-dirty work-around, I've changed the original snippet:

_growroot() {
        # Remove 'block:' prefix and find the root device
        rootdev=$(readlink -f "${root#block:}")


with:

> _growroot() {
> 	# Compute root-device
> 	if [ -z "${root##*mapper*}" ]
> 	then
> 		set -- "${root##*mapper/}"
> 		VOLGRP=${1%-*}
> 		ROOTVOL=${1#*-}
> 		rootdev=$(readlink -f $(pvs --noheadings | awk '/'${VOLGRP}'/{print $1}'))
> 		_info "'/' is hosted on an LVM2 volume: setting \$rootdev to ${rootdev}"
> 	else
> 		# Remove 'block:' prefix and find the root device
> 		rootdev=$(readlink -f "${root#block:}")
> 	fi


In mine. Obviously, it assumes that "/" will never span multiple PVs, so, probably wants some cleanup.

Further note: while the above code-change allows the grow-root against the partition containing the PV hosting "/" to succeed, it typically requires a reboot to fully-effect: first boot grows what is seen by sfdisk; second boot grows what is seen by lsblk (and pvresize).