Comment 4 for bug 1257467

Reviewed: https://review.openstack.org/229159
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=3837427189a54e6c052d773d629bac53d95702dc
Submitter: Jenkins
Branch: master

commit 3837427189a54e6c052d773d629bac53d95702dc
Author: David Edery <email address hidden>
Date: Mon Oct 12 11:11:50 2015 +0300

    Enable specific extra_dhcp_opt to be left blank

    In some cases there is a need for a blank value of the "router" extra
    dhcp option. This fix addresses this issue by introducing a simple
    mechanism in the code that allows specific extra dhcp options to be left
    blank by applying a different opt_value validation of the data received
    from the REST call and different validation on the value that will be
    written to the DB.

    This fix also takes into consideration bug #1257467 which claims that
    in case of a blank "server-ip-address" option a segmentation fault
    occurs in dnsmasq. I did not check this claim with a newer dnsmasq
    version since it seemed logical that the list of potentially blank
    options should be limited to options that are known to work well when
    blank and have functional justification for being blank (e.g. "router")

    APIImpact
    "router" and "classless-static-route" extra dhcp options can be blank
    (e.g. opt-name="router", opt-value="")

    DocImpact
    During port creation/update, Specific extra-dhcp-options can be left
    blank ("router" and/or "classless-static-route"). This causes dnsmasq
    to have an empty option in the "opts" file related to the network to
    which the port is related.
    For example:
    tag:tag0,option:classless-static-route,
    tag:tag0,option:router,

    Closes-Bug: #1437695
    Related-Bug: #1257467

    Change-Id: I0ac76e132c4bd86da39863674d4cf8a22dad7034