DLPX-73192 Establish appropriate systemd service dependencies for iSCSI initiator

[don-brady]

Description

This makes the open-iscsi service service stop operation zfs aware. Here we want to make sure ZFS is still not actively using an iSCSI device. When restarting (or stopping) the open-iscsi service, the iscsi devices are torn completely down. Then during start these devices are rebuilt; they typically have a different device node (sdN). Note that an open-iscsi stop operation already checks for mounted file systems that are backed by iscsi devices but those checks are not ZFS aware.

We introduce a new check script, zpool_on_iscsi.sh, which is similar to the existing umountiscsi.sh script. This new script will return a non-zero result (1) if there is a zfs pool using iSCSI devices which in turn will prevent the open-iscsi service from stopping. The service will log the failure as seen below.

Jan 14 02:00:04  systemd[1]: Stopping Login to default iSCSI targets...
Jan 14 02:00:04  zpool_on_iscsi.sh [25638]: device '/dev/sde1' in use by zfs pool 'domain0'
Jan 14 02:00:04  systemd[1]: open-iscsi.service: Control process exited, code=exited status=1
Jan 14 02:00:04  systemd[1]: open-iscsi.service: Failed with result 'exit-code'.

We expect that most iSCSI administration will be performed using the Delphix iSCSI APIs and that in general no admin should be directly stopping or restarting the open-iscsi service.

Testing Done

Ab-pre-push:
http://selfservice.jenkins.delphix.com/job/devops-gate/job/master/job/appliance-build-orchestrator-pre-push/4641/

Manual Testing:

• Confirmed override.conf file was correctly installed and that systemctl cat shows override is present
• Confirmed that when the pool is imported, that stopping open-iscsi service will fail and the pool remains accessible
• Confirmed that after the domain0 pool is exported, then a stop of open-iscsi service proceeds and the iscsi devices are no longer present (lsblk).
• Confirmed that on a reboot the system was able to shutdown (i.e. the zpool_on_iscsi.sh check doesn't prevent shutting down)
• Ran both shellcheck and shfmt against the new script.

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

An open-iscsi stop will tear down the devices while still being used by zfs and the pool will become suspended

What is the new behavior?

stopping open-iscsi service will fail and the pool remains accessible

Does this introduce a breaking change?

• Yes
• No