[Bug 2029952] [NEW] [SRU] backport msgpack max_buffer_size patch to Focal

[Edward Hope-Morley]

Public bug reported:

[Impact]
Hosts running Openstack Neutron from Ussuri to Yoga release are impacted by
the fact that their use of oslo.privsep is thwarted by a default buffer size
on python-msgpack such that commands that return strings > 1MB in size cause
privsep to crash and agents to stop working. This patch backports a fix that
increased the buffer size to one that is more appropriate to neutron usage.

[Test Plan]

  * deploy Openstack (version corresponding to release of SRU) with l3ha
  * need at least one compute host and two neutron-gateway hosts
  * create a large number of routers each with several networks attached
  * restart neutron-l3-agent
  * wait for restart to complete then do 'journalctl --unit neutron-l3-agent --grep ValueError'
  * if the error does not appear then the patch is working
  * note that it is necessary to create routers with enough networks and ports to trigger the > 1MB size limit for the netlink info message returned by privsep to trigger

[Where problems could occur]
No regressions are expected to occur as a result of this patch as it is
increasing the buffer size by a fairly small amount to allow neutron
function correctly in loaded environments.

--------------------------------------------------------------------------------

The main explanation for this backport can be found in
https://bugs.launchpad.net/ubuntu/+source/python-
oslo.privsep/+bug/1896734/comments/37 but I'm opening a new bug for the
privsep backport since 1896734 was used to backport a neutron fix.

** Affects: cloud-archive
     Importance: Undecided
         Status: New

** Affects: cloud-archive/ussuri
     Importance: Undecided
         Status: New

** Affects: cloud-archive/victoria
     Importance: Undecided
         Status: New

** Affects: cloud-archive/wallaby
     Importance: Undecided
         Status: New

** Affects: cloud-archive/xena
     Importance: Undecided
         Status: New

** Affects: cloud-archive/yoga
     Importance: Undecided
         Status: New

** Affects: python-oslo.privsep (Ubuntu)
     Importance: Undecided
         Status: New

** Affects: python-oslo.privsep (Ubuntu Focal)
     Importance: Undecided
         Status: New

** Affects: python-oslo.privsep (Ubuntu Jammy)
     Importance: Undecided
         Status: New

** Also affects: python-oslo.privsep (Ubuntu Jammy)
   Importance: Undecided
       Status: New

** Also affects: python-oslo.privsep (Ubuntu Focal)
   Importance: Undecided
       Status: New

** Also affects: cloud-archive
   Importance: Undecided
       Status: New

** Also affects: cloud-archive/wallaby
   Importance: Undecided
       Status: New

** Also affects: cloud-archive/yoga
   Importance: Undecided
       Status: New

** Also affects: cloud-archive/victoria
   Importance: Undecided
       Status: New

** Also affects: cloud-archive/ussuri
   Importance: Undecided
       Status: New

** Also affects: cloud-archive/xena
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/2029952

Title:
  [SRU] backport msgpack max_buffer_size patch to Focal

Status in Ubuntu Cloud Archive:
  New
Status in Ubuntu Cloud Archive ussuri series:
  New
Status in Ubuntu Cloud Archive victoria series:
  New
Status in Ubuntu Cloud Archive wallaby series:
  New
Status in Ubuntu Cloud Archive xena series:
  New
Status in Ubuntu Cloud Archive yoga series:
  New
Status in python-oslo.privsep package in Ubuntu:
  New
Status in python-oslo.privsep source package in Focal:
  New
Status in python-oslo.privsep source package in Jammy:
  New

Bug description:
  [Impact]
  Hosts running Openstack Neutron from Ussuri to Yoga release are impacted by
  the fact that their use of oslo.privsep is thwarted by a default buffer size
  on python-msgpack such that commands that return strings > 1MB in size cause
  privsep to crash and agents to stop working. This patch backports a fix that
  increased the buffer size to one that is more appropriate to neutron usage.

  [Test Plan]

    * deploy Openstack (version corresponding to release of SRU) with l3ha
    * need at least one compute host and two neutron-gateway hosts
    * create a large number of routers each with several networks attached
    * restart neutron-l3-agent
    * wait for restart to complete then do 'journalctl --unit neutron-l3-agent --grep ValueError'
    * if the error does not appear then the patch is working
    * note that it is necessary to create routers with enough networks and ports to trigger the > 1MB size limit for the netlink info message returned by privsep to trigger

  [Where problems could occur]
  No regressions are expected to occur as a result of this patch as it is
  increasing the buffer size by a fairly small amount to allow neutron
  function correctly in loaded environments.

  --------------------------------------------------------------------------------

  The main explanation for this backport can be found in
  https://bugs.launchpad.net/ubuntu/+source/python-
  oslo.privsep/+bug/1896734/comments/37 but I'm opening a new bug for
  the privsep backport since 1896734 was used to backport a neutron fix.

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