Error mounting device on create instance (LXC)

[Miguel Ángel Herranz Trillo]

Description
===========

After installing Openstack in Ubuntu 18.04 and using LXC as virtualization engine, the creation of an instance fails with a log in `nova-compute.log` reporting that:

 ```Instance failed to spawn: TypeError: mount() takes exactly 4 arguments (3 given)```

Extra analysis of the logs an code points towards this file of `python-nova` package:

 /usr/lib/python2.7/dist-packages/nova/virt/disk/mount/api.py

The problem seems that the call at line 251

```
   246 def mnt_dev(self):
   247 """Mount the device into the file system."""
   248 LOG.debug("Mount %(dev)s on %(dir)s",
   249 {'dev': self.mapped_device, 'dir': self.mount_dir})
   250 out, err = nova.privsep.fs.mount(None, self.mapped_device,
   251 self.mount_dir)
   252 if err:
   253 self.error = _('Failed to mount filesystem: %s') % err
   254 LOG.debug(self.error)
   255 return False
   256
   257 self.mounted = True
   258 return True
```

is not matching the function signature defined in /usr/lib/python2.7/dist-packages/nova/privsep/fs.py as:

```
    30 def mount(fstype, device, mountpoint, options):
    31 mount_cmd = ['mount']
    32 if fstype:
    33 mount_cmd.extend(['-t', fstype])
    34 if options is not None:
    35 mount_cmd.extend(options)
    36 mount_cmd.extend([device, mountpoint])
    37 return processutils.execute(*mount_cmd)
```

So, it should be safe just to add `None` as `options` parameter.

Steps to reproduce
==================

Environment info:

  OS: Ubuntu 18.04.2 LTS
  Kernel: Linux 4.15.0-46-generic #49-Ubuntu SMP x86_64
  Openstack: queens

  Related packages versions:

  nova-api: Installed: 2:17.0.9-0ubuntu1
  python-nova: Installed: 2:17.0.9-0ubuntu1
  nova-compute: Installed: 2:17.0.9-0ubuntu1
  nova-compute-lxc: Installed: 2:17.0.9-0ubuntu1

Command executed to create the instance:

```
# openstack server create --flavor lxc.small --image lxc_ubuntu_18.04 --nic net-id=${NEUTRON_NETWORK_NAT_ID} --security-group default --key-name vagrant test_lxc_instance
+-------------------------------------+---------------------------------------------------------+
| Field | Value |
+-------------------------------------+---------------------------------------------------------+
| OS-DCF:diskConfig | MANUAL |
| OS-EXT-AZ:availability_zone | |
| OS-EXT-SRV-ATTR:host | None |
| OS-EXT-SRV-ATTR:hypervisor_hostname | None |
| OS-EXT-SRV-ATTR:instance_name | |
| OS-EXT-STS:power_state | NOSTATE |
| OS-EXT-STS:task_state | scheduling |
| OS-EXT-STS:vm_state | building |
| OS-SRV-USG:launched_at | None |
| OS-SRV-USG:terminated_at | None |
| accessIPv4 | |
| accessIPv6 | |
| addresses | |
| adminPass | GhYewcoXch3w |
| config_drive | |
| created | 2019-05-17T10:00:57Z |
| flavor | lxc.small (0) |
| hostId | |
| id | fe69997d-10c2-4850-bdba-2468da7148d6 |
| image | lxc_ubuntu_18.04 (de3ca120-42f6-47a2-be1b-65c7276f1566) |
| key_name | vagrant |
| name | test_lxc_instance |
| progress | 0 |
| project_id | 4c2cf8fa37c8451d87ddd2cf28cfd6bc |
| properties | |
| security_groups | name='35a8788c-364b-4da3-9c26-4aebf0ac04c4' |
| status | BUILD |
| updated | 2019-05-17T10:00:57Z |
| user_id | 0d48615bb8c747f4b5ec5bfc693b6832 |
| volumes_attached | |
+-------------------------------------+---------------------------------------------------------+
```

Expected result
===============
```
# openstack server list
+--------------------------------------+-------------------+--------+-----------------+------------------+-----------+
| ID | Name | Status | Networks | Image | Flavor |
+--------------------------------------+-------------------+--------+-----------------+------------------+-----------+
| dac7b2b8-841b-4a16-a54f-2d5177f05934 | test_lxc_instance | ACTIVE | nat=10.123.1.11 | lxc_ubuntu_18.04 | lxc.small |
+--------------------------------------+-------------------+--------+-----------------+------------------+-----------+
```

Actual result
=============
```
# openstack server list
+--------------------------------------+-------------------+--------+----------+------------------+-----------+
| ID | Name | Status | Networks | Image | Flavor |
+--------------------------------------+-------------------+--------+----------+------------------+-----------+
| fe69997d-10c2-4850-bdba-2468da7148d6 | test_lxc_instance | ERROR | | lxc_ubuntu_18.04 | lxc.small |
+--------------------------------------+-------------------+--------+----------+------------------+-----------+
```

Logs
====

Included some logs generated during the command, and retrieved using:

```
grep -r "2019-05-17 10:0[01]" /var/log >> openstack_queens_lxc_instance_creation_mount_error.logs
```

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/659780

[Matt Riedemann (mriedem)]

This is a regression since Queens:

https://review.opendev.org/#/c/494423/

I'm marking it as medium priority but it could probably just as well be low priority given I haven't heard of someone trying to use the libvirt+lxc configuration in years.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/659780
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=d2ef1ce309c28a5416af4cc00662ad6925574004
Submitter: Zuul
Branch: master

commit d2ef1ce309c28a5416af4cc00662ad6925574004
Author: Miguel Herranz <email address hidden>
Date: Fri May 17 12:53:10 2019 +0200

    Fix type error on call to mount device

    The call in nova.virt.disk.mount.api.Mount.mnt_dev() to
    nova.privsep.fs.mount() should include the `options` argument to
    fulfill with the method signature.

    The test test_do_mount_need_to_specify_fs_type has been modified to
    check that the caller use the correct signature.

    Closes-Bug: 1829506

    Change-Id: Id14993db6ea33b2da14caa4b58671fc57c182706
    Signed-off-by: Miguel Herranz <email address hidden>

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/stein
Review: https://review.opendev.org/667921

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/667921
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=8371073ac7a3439ea5b6ce9091a91e77cf88020e
Submitter: Zuul
Branch: stable/stein

commit 8371073ac7a3439ea5b6ce9091a91e77cf88020e
Author: Miguel Herranz <email address hidden>
Date: Fri May 17 12:53:10 2019 +0200

    Fix type error on call to mount device

    The call in nova.virt.disk.mount.api.Mount.mnt_dev() to
    nova.privsep.fs.mount() should include the `options` argument to
    fulfill with the method signature.

    The test test_do_mount_need_to_specify_fs_type has been modified to
    check that the caller use the correct signature.

    Closes-Bug: 1829506

    Change-Id: Id14993db6ea33b2da14caa4b58671fc57c182706
    Signed-off-by: Miguel Herranz <email address hidden>
    (cherry picked from commit d2ef1ce309c28a5416af4cc00662ad6925574004)

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/queens
Review: https://review.opendev.org/669629

[Miguel Ángel Herranz Trillo (maherranzt)]

Cherry picked from master branch to stable/queens branch: https://review.opendev.org/#/c/669629/1

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/rocky
Review: https://review.opendev.org/669664

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/669664
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=e3cd1d9baa74181cbac1765291ad67654b35721d
Submitter: Zuul
Branch: stable/rocky

commit e3cd1d9baa74181cbac1765291ad67654b35721d
Author: Miguel Herranz <email address hidden>
Date: Fri May 17 12:53:10 2019 +0200

    Fix type error on call to mount device

    The call in nova.virt.disk.mount.api.Mount.mnt_dev() to
    nova.privsep.fs.mount() should include the `options` argument to
    fulfill with the method signature.

    The test test_do_mount_need_to_specify_fs_type has been modified to
    check that the caller use the correct signature.

    Closes-Bug: 1829506

    Change-Id: Id14993db6ea33b2da14caa4b58671fc57c182706
    Signed-off-by: Miguel Herranz <email address hidden>
    (cherry picked from commit d2ef1ce309c28a5416af4cc00662ad6925574004)
    (cherry picked from commit 8371073ac7a3439ea5b6ce9091a91e77cf88020e)

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/669629
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=f77c628b4f08a625bebe8b8b3bb24a8e9784a226
Submitter: Zuul
Branch: stable/queens

commit f77c628b4f08a625bebe8b8b3bb24a8e9784a226
Author: Miguel Herranz <email address hidden>
Date: Fri May 17 12:53:10 2019 +0200

    Fix type error on call to mount device

    The call in nova.virt.disk.mount.api.Mount.mnt_dev() to
    nova.privsep.fs.mount() should include the `options` argument to
    fulfill with the method signature.

    The test test_do_mount_need_to_specify_fs_type has been modified to
    check that the caller use the correct signature.

    Closes-Bug: 1829506

    Change-Id: Id14993db6ea33b2da14caa4b58671fc57c182706
    Signed-off-by: Miguel Herranz <email address hidden>
    (cherry picked from commit d2ef1ce309c28a5416af4cc00662ad6925574004)
    (cherry picked from commit 8371073ac7a3439ea5b6ce9091a91e77cf88020e)
    (cherry picked from commit e3cd1d9baa74181cbac1765291ad67654b35721d)

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/nova 19.0.2 release.

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/nova 18.2.2 release.

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/nova 17.0.12 release.

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/nova 20.0.0.0rc1 release candidate.