LVM.__init__() checks for VG existence before setting up LVM_SYSTEM_DIR

[Fergal Mc Carthy]

Running Kilo Stable version of OpenStack

While testing on a small OpenStack configuration using LVM as a backend I have configured the /etc/lvm/lvm.conf on my hosts to reject all devices except those on which the operating system is installed.

On the host where cinder-volume & cinder-backup are running I created a /etc/cinder/lvm.conf which rejects all devices except those backing the cinder-volumes LVM VG. I.e. there is no overlap between the set of devices accepted by /etc/lvm/lvm.conf and /etc/cinder/lvm.conf.

When I try to start cinder-volume I get errors trying to initalise the LVM backend because the specified backing LVM VG is not found.

Looking in the logs I noticed that even though /etc/cinder/lvm.conf exists and was specified via the lvm_conf_file option, there is a 'vgs' command being run without LVM_SYSTEM_DIR specified in it's environment.

This lead me to the 'cinder/brick/local_dev/lvm.py' file where I noticed that, in the middle of the LVM.__init__(), there is a self._vg_exists() check, but the LVM.LVM_CMD_PREFIX isn't updated to include LVM_SYSTEM_DIR until the end of the LVM.__init__() routine, as follows:

        if lvm_conf and os.path.isfile(lvm_conf):
            LVM.LVM_CMD_PREFIX = ['env',
                                  'LC_ALL=C',
                                  'LVM_SYSTEM_DIR=/etc/cinder']

Moving these 4 lines of code to before the create_vg check near the beginning of LVM.__init__() resolved the problem and allows me to start cinder-volume.

I notice that this code appears the same on the cinder/master branch, so I will propose a review for this against that branch later today.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/226543

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/226543
Committed: https://git.openstack.org/cgit/openstack/cinder/commit/?id=adf2d4306a6886268ffb1a6e4c8fe7ef2fe683e3
Submitter: Jenkins
Branch: master

commit adf2d4306a6886268ffb1a6e4c8fe7ef2fe683e3
Author: Fergal Mc Carthy <email address hidden>
Date: Tue Sep 22 16:39:48 2015 -0400

    Setup LVM_SYSTEM_DIR earlier in LVM.__init()

    When using a Cinder specific lvm.conf file, we need to setup the
    LVM_SYSTEM_DIR setting in the LVM.LVM_CMD_PREFIX before issuing
    any LVM commands to ensure that the correct lvm.conf is used.

    The issue was uncovered when testing on a Cinder Volume host setup
    as follows:
      * Cinder is configured to use an LVM backend, backed by the
        cinder-volumes VG, which already exists.
      * /etc/lvm/lvm.conf rejects all devices other than those on which
        the operating system is installed.
      * /etc/cinder/lvm.conf accepts only the devices backing the
        cinder-volumes LVM VG

    The cinder-volume service would fail to initialise the specified LVM
    backend because the cinder.brick.local_dev.lvm.LVM.__init__() call
    checks for the existence of the specified VG before
        LVM_SYSTEM_DIR=/etc/cinder
    has been added to the LVM.LVM_CMD_PREFIX, and thus fails to find the
    VG, and raises an exception.

    By moving the setup of the LVM_SYSTEM_DIR environment variable in
    LVM.LVM_CMD_PREFIX to happen before any LVM commands are issued we
    ensure that all subsequent LVM commands are run against the correct
    lvm.conf file.

    Change-Id: I6551b045ab48ee60c3ee4cd15c13058635c144c2
    Closes-Bug: #1498480

[Thierry Carrez (ttx)]

This issue was fixed in the openstack/cinder 8.0.0.0b1 development milestone.