[Bug 1921658] Re: Can't compose kvm host with lvm storage on maas 2.8.4

[Robie Basak]

SRU review

I don't see any explanation anywhere of what exactly is wrong in
readline in Bionic or how it is being fixed. Normally I would expect to
see such an explanation in both the SRU template and in the upstream
patch description that is being cherry-picked. But in this case neither
are present.

I don't think it's appropriate to SRU this without a full understanding
of what is going on - especially when it's such a common library being
patched. In particular, I don't think it's possible to assess regression
risk with any confidence without a full understanding of what is being
changed and why.

Please could you expand on this?

** Changed in: readline (Ubuntu Bionic)
       Status: In Progress => Incomplete

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Title:
  Can't compose kvm host with lvm storage on maas 2.8.4

Status in MAAS:
  Triaged
Status in readline package in Ubuntu:
  Fix Released
Status in readline source package in Bionic:
  Incomplete

Bug description:
  [Impact]

  I can't compose kvm host on maas 2.8.4 ( bionic)

  I upgraded twisted and related component with pip but the symptom is
  the same.

  MaaS 2.9.x in Focal works fine.

  in 2.8.x, pexpect virsh vol-path should return [2] but returns [3]

  [2]
  /dev/maas_data_vg/8d4e8b04-4031-4a1b-b5f2-a8306192db11
  [3]
  2021-03-17 20:43:34 stderr: [error] Message: 'this is the result...\n'
  2021-03-17 20:43:34 stderr: [error] Arguments: ([' ', '<3ef-46ca-87c8-19171950592f --pool maas_guest_lvm_vg', "error: command 'attach-disk' doesn't support option --pool"],)

  sometimes it fails in

      def get_volume_path(self, pool, volume):
          """Return the path to the file from `pool` and `volume`."""
          output = self.run(["vol-path", volume, "--pool", pool])
          return output.strip()

  sometimes failes in

      def get_machine_xml(self, machine):
          # Check if we have a cached version of the XML.
          # This is a short-lived object, so we don't need to worry about
          # expiring objects in the cache.
          if machine in self.xml:
              return self.xml[machine]

          # Grab the XML from virsh if we don't have it already.
          output = self.run(["dumpxml", machine]).strip()
          if output.startswith("error:"):
              maaslog.error("%s: Failed to get XML for machine", machine)
              return None

          # Cache the XML, since we'll need it later to reconfigure the VM.
          self.xml[machine] = output
          return output

  I assume that run function has issue.

  Command line virsh vol-path and simple pepect python code works fine.

  Any advice for this issue?

  Thanks.

  [Test Plan]

  0) deploy Bionic and MAAS 2.8

  1) Create file to be used as loopback device

  sudo dd if=/dev/zero of=lvm bs=16000 count=1M

  2) sudo losetup /dev/loop39 lvm

  3) sudo pvcreate /dev/loop39

  4) sudo vgcreate maas_data_vg /dev/loop39

  5) Save below xml:
  <pool type='logical'>
  <name>maas_guest_lvm_vg</name>
  <source>
  <name>maas_data_vg</name>
  <format type='lvm2'/>
  </source>
  <target>
  <path>/dev/maas_data_vg</path>
  </target>
  </pool>

  6) virsh pool-create maas_guest_lvm_vg.xml

  7) Add KVM host in MaaS

  8) Attempt to compose a POD using storage pool maas_guest_lvm_vg

  9) GUI will fail with:

  Pod unable to compose machine: Unable to compose machine because:
  Failed talking to pod: Start tag expected, '<' not found, line 1,
  column 1 (<string>, line 1)

  [Where problems could occer]

  This patch is small peice of huge commit.
  I tested by compiling test pkg with this patch. but actually it is kind of underlying library ( libreadline ), so It could affect to any application using libreadline.
  e.g running command inside application by code can be affected.

  
  [Other Info]

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