why is tmpfs not present when switching into mfs

[dch]

Despite having tmpfs.ko in kernel by default, when, at end of mfsroot, we try to re-root, tmpfs is not found. this requires us to have it duplicated both in EFI: /boot/kernel/tmpfs.ko and inside the mfsroot. And on the main disk image. So triplicated, which is messy for keeping in sync.

If this is addressed, then the mfsroot only contains the rescue files, and they change rarely which makes updating an existing deployed box significantly easier.

https://cgit.freebsd.org/src/commit/?id=b798ef6 shows that tmpfs is included in GENERIC.

During boot, we see this https://github.com/skunkwerks/oci-a1-metal/wiki/Boot-Log#serial-console

...
mce0: Ethernet address: b8:ce:f6:4c:2a:76
mce0: link state changed to DOWN
mce1: Ethernet address: b8:ce:f6:4c:2a:77
mce1: link state changed to DOWN
sysctl_unregister_oid: failed(22) to unregister sysctl(tmpfs)

If tmpfs.ko is removed from mfsroot then we see this:

module_register_init: MOD_LOAD (tmpfs, 0xffff000000551414, 0xffff000000acc680) error 17
...
+ reboot -r
- init 1 - - cannot mount tmpfs on /dev/reroot: Invalid fstype: Invalid argument
- init 1 - - reroot failed; going to single user mode