zfsbootmenu: warn when canmount=on is set for root dataset

[zdykstra]

Root datasets should never be automatically mounted. Anything that is considered a root dataset (regardless of a valid kernel/initramfs pair being present) should be checked for canmount=on being set. If it is, throw up a zwarn() . This possibly needs to be more aggressively warned via a timed_prompt - forcing user interaction.

[ahesford]

I think a subtle warning like this or a more obvious, passive indicator is fine. I don't know that we should interrupt regular flow with a timed prompt.

[ahesford]

I think a subtle warning like this or a more obvious, passive indicator is fine. I don't know that we should interrupt regular flow with a timed prompt.

[zdykstra]

Yeah. If we continue to see people impacted by this, the warning can be re-evaluated. For now, a normal warning delivered via the common mechanism is a good start.

[ahesford]

How about this: count the number of root filesystems; if there is exactly one and has canmount=auto, use the unobtrusive logged warning. If there are more than one and any of them have canmount=auto, throw up a timed prompt warning the user that these may fail to boot.

[zdykstra]

I'm checking for the wrong condition - whoops. I'll rework this to count and set a flag file that zfsbootmenu-init can check for.