RbxCloud: Add support for FreeBSD

[ad-m]

Changes are made that simplify code and aim to properly support FreeBSD:

• use util.find_devs_with instead call directly blkid, because on FreeBSD is not supported well and util.find_devs_with have solution for FreeBSD for that
• introduction of an additional name on FAT file system, which is used in FreeBSD
• drop shell to use default value, because FreeBSD – by default – does not have /bin/bash

[igalic]

Good catch!

[OddBloke]

This is a small change in behaviour on Linux-based systems: the previous code would match 'CLOUDMD' case-insensitively, whereas the new code requires upper-case:

$ ls /dev/disk/by-label -lah
...
lrwxrwxrwx 1 root root  15 Jun 29 08:38  SYSTEM -> ../../nvme0n1p1
...
$ python3 -c 'from cloudinit import util; print(util.find_devs_with("LABEL=system"))'
[]
$ python3 -c 'from cloudinit import util; print(util.find_devs_with("LABEL=SYSTEM"))'
['/dev/nvme0n1p1']

Is this an issue, practically speaking?

(If this change is acceptable, we should also update ds-identify to match the more stringent case requirements.)

[ad-m]

In our environment, we've been providing clients with images only marked as CLOUDMD for years. The documentation in this area was also consistent always. I have not encountered (but we have no right to scan customer environments) a different situation.

I wonder at what stage the case insensitivity should be implemented. I notice that:

• ConfigDrive supports both: https://github.com/canonical/cloud-init/blob/master/cloudinit/sources/DataSourceConfigDrive.py#L30
• NoCloud supports both: https://github.com/canonical/cloud-init/blob/master/cloudinit/sources/DataSourceNoCloud.py#L42-L43

At the same time:

• OpenNebula supports one format: https://github.com/canonical/cloud-init/blob/master/cloudinit/sources/DataSourceOpenNebula.py#L268
• OpenStack supports one format: https://github.com/canonical/cloud-init/blob/master/cloudinit/sources/helpers/openstack.py#L108

Considering diversity, it will adapt code of datasource to support both formats nor utils itself.

[OddBloke]

LGTM, thanks!