EFI boot with multiple alternate boot/OS partitions - possible?

[Warner Losh]

On Fri, Nov 30, 2018 at 7:26 AM Milan Obuch <freebsd-hackers at dino.sk> wrote:

> Hi,
>
> I am working on a project using relatively simple workstation,
> basically web browser with custom backend, running page with javascript
> communicating with said backend to display status of some processes
> (customer's technology aka real world) being supervised. Current
> prototype uses UP2 board with 32 GB eMMC, where EFI BIOS is used.
>
> So far so good, everything runs to project manager's satisfaction, just
> there is one problem to solve - UPS is not used in order to keep
> installation simpler and cost lower, so I need to find a way how to run
> everything from read-only mounted file systems, but occasional update
> could be requested.
>
> It is manageable when dealing with application/libraries, both from
> ports and custom programms, but if OS partition is to be upgraded,
> maybe for security reason or the like, power outage in wrong instant
> could render whole system unusable. In order to minimise risks with
> such an upgrade, I would like to employ following scheme:
>
> (partial partition layout from gpart show)
>
>         40    409600      1  efi  (200M)
>     409640   3145728      2  freebsd-ufs  (1.5G)
>    3555368   3145728      3  freebsd-ufs  (1.5G)
>    6701096   8388608      4  freebsd-swap  (4.0G)
>
> (other partition for application data, cache etc)
>
> with /etc/fstab corresponding part being
>
> # Device      Mountpoint  FStype  Options  Dump  Pass#
> /dev/sdda0p2  /           ufs     ro       1     1
> /dev/sdda0p3  /alt        ufs     ro       2     2
> /dev/sdda0p4  none        swap    sw       0     0
>
> When upgrade request is being handled, /alt filesystem is being remount
> with read-write access, receives whole OS installation, relevant config
> files in /etc directory are being copied into /alt/etc directory,
> resulting in usable alternate OS copy. This can be verified for
> accuracy etc. and system should be switched to use partition 3 for
> next boot, something like nextboot command with -k option makes, but
> whole partition, not just directory with kernel is switched...
>
> Then partitions' roles are swapped, as /etc/fstab file in now active
> secondary partition would be
>
> # Device      Mountpoint  FStype  Options  Dump  Pass#
> /dev/sdda0p2  /alt        ufs     ro       2     2
> /dev/sdda0p3  /           ufs     ro       1     1
> /dev/sdda0p4  none        swap    sw       0     0
>
> Any ideas/hints would be appreciated, I tried to look into efibootmgr
> and efivar man pages, but got no clear idea how they could be used for
> my purpose. I do not fully understand some details of EFI boot process,
> so if some good material for reading is available, let me know (I did
> some googling, but found no definitive answers yet).
>

efibootmgr is what you want, though if it's under-documented we should fix
that. Assuming that p1 is the ESP, you should be able to do:

efibootmgr -c -l ssd0p1:/efi/freebsd/loader.efi -k
ssd0p3:/boot/kernel/kernel -b 10 -a
efibootmgr -c -l ssd0p1:/efi/freebsd/loader.efi -k
ssd0p2:/boot/kernel/kernel -b 11 -a

this will setup Boot0010 and Boot0011.

You can then set the order either with efibootmgr  -o or efibootmgr -n. In
theory you can also use the full unix path for the -k and -l lines if
things are mounted, but I hadn't fixed all the weird edge cases with that
which kept cropping up (I think they are are fixed since I can't recreate
the problems, but I'm not 100% sure).

Extra caveat: This only works for UEFI implementations that have persistent
env vars. And non-broken UEFI BootMgr implementations. Supermicro has a
broken one that one needs to work around in various ugly ways (they won't
fix it, since they think it's a feature, but they are wrong).

Warner


> Or should I modify my partitions by inserting second efi, so the result
> would be like
>
>         40    409600      1  efi  (200M)
>     409640   3145728      2  freebsd-ufs  (1.5G)
>    xxxxx68    409600      3  efi  (200M)
>    xxxxx68   3145728      4  freebsd-ufs  (1.5G)
>    xxxxx96   8388608      5  freebsd-swap  (4.0G)
>
> and EFI BIOS will see those two efi partitions as two independent
> systems allowing me to switch them with some BootOrder vars? I would
> like to avoid having two efi partitions, 200 MB basically wasted space
> is not too much in today's devices, but as the whole eMMC is 32 GB in
> size, it is not negligible, it could be missed sometimes...
>
> Regards,
> Milan
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