Return value of shell commands is not checked by plugins

[Maru Newby]

Plugin agents (linuxbridge, ovs, ryu) use a copied implementation of run_cmd to execute shell commands. None of the implementations check the return value of an executed command, which has the potential to violate the dictates of 'fail fast' and complicate debugging.

As a simple example, a missing command will normally cause Popen to raise OSError. If a root_helper like sudo is used, however, no such error is raised and the exit code and/or stderror output are the only indications that something is wrong. None of the plugins check the exit code or stderr output by default.

nova.util.execute() is the benchmark here - exit codes are checked by default, and can only be ignored on a code-by-code basis.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/8033

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/8033
Committed: http://github.com/openstack/quantum/commit/0230e96196baf4cfd4cb7f556539fe6758367176
Submitter: Jenkins
Branch: master

commit 0230e96196baf4cfd4cb7f556539fe6758367176
Author: Juliano Martinez <email address hidden>
Date: Thu Jun 7 17:56:07 2012 -0300

    Bug #1000406 - Return value of shell commands is not checked by plugins

    Added an utils library for agents and also changed agents to use
    this library.

    Changed to keep 2.4 compatibility

    Change-Id: Ib4fc0a8dcbfc4b79a0b0e61e1fc1f24ec5da4d46

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/9203
Committed: http://github.com/openstack/quantum/commit/4742e34a8979d4a9ddb8ea58c0f2c5448723a6fb
Submitter: Jenkins
Branch: master

commit 4742e34a8979d4a9ddb8ea58c0f2c5448723a6fb
Author: Gary Kotton <email address hidden>
Date: Sun Jul 1 03:06:07 2012 -0400

    Check if interface exists in bridge prior to adding.

    This fixes bug 1019730. The fix for bug 1000406 ensures that return
    values of shell commands are checked. The command
        utils.execute(['brctl', 'addif', bridge_name, interface],
                       root_helper=self.root_helper)
    would cause an exception if there was more than one attachment
    on the network. The reason for this was the interface already existed
    on the bridge.

    Change-Id: I8a1f6cc7be930c04ce302d7f87814b9bd5bed129