LinuxInterfaceDriver plug method in derived class already check for device existence

[Rossella Sblendido]

LinuxInterfaceDriver plug in derived classes already check if the device exists. There's no need to duplicate the check in the code that is calling those methods. See l3_agent.py in internal_network_added for example:

        if not ip_lib.device_exists(interface_name,
                                    root_helper=self.root_helper,
                                    namespace=ri.ns_name):
            self.driver.plug(network_id, port_id, interface_name, mac_address,
                             namespace=ri.ns_name,
                             prefix=INTERNAL_DEV_PREFIX)

the check "if not ip_lib.device_exists" is a duplicate and it's expensive.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/113897

[OpenStack Infra (hudson-openstack)]

Related fix proposed to branch: master
Review: https://review.openstack.org/116588

[OpenStack Infra (hudson-openstack)]

Change abandoned by Salvatore Orlando (<email address hidden>) on branch: master
Review: https://review.openstack.org/113897
Reason: This patch has been inactive long enough that I think it's safe to abandon.
The author can resurrect it if needed.

[OpenStack Infra (hudson-openstack)]

Change abandoned by Salvatore Orlando (<email address hidden>) on branch: master
Review: https://review.openstack.org/116588
Reason: This patch has been inactive long enough that I think it's safe to abandon.
The author can resurrect it if needed.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/147554

[Salvatore Orlando (salvatore-orlando)]

The fact that plug verifies that device exists is a characteristic of all the implementations of LinuxInterfaceDriver, where plug is actually abstract.

I agree that there is an unnecessary duplicate check here.
I am ok with declaring that verifying that an interface exists before plugging is the responsability of the driver. This should be however documented, since in theory one could use his own custom driver (interface_driver is a configuration parameter).

Moreover since LinuxInterfaceDriver can use ip_lib perhaps the check should be done in the base class thus also removing some repeated logic in the various drivers.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/147554
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=6b4d006344e38dcbbc0048b17ca41af16e13e5a2
Submitter: Jenkins
Branch: master

commit 6b4d006344e38dcbbc0048b17ca41af16e13e5a2
Author: Sergey Belous <email address hidden>
Date: Thu Jan 15 18:19:51 2015 +0300

    Refactor checks for device existence

    The code calling driver.plug() shouldn't check for the device existence,
    it's a duplicate and it's an expensive call.
    Move check for device existence to base LinuxInterfaceDriver.plug()
    to remove code duplication. Make plug_new() abstract instead.

    Change-Id: Id118a64012ad10b197ba681ce5f1b2742eb135b4
    Closes-Bug:1348703

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: neutron-pecan
Review: https://review.openstack.org/185072