[arch-general] Installation: How to get HDD > LUKS > GPT working in a clean way

[Merlin Büge]

Hey everybody!


I'm currently installing Arch on my laptop (Thinkpad T400), and have decided
for a rather unusual partition scheme: A single LUKS container directly on
the disk (SSD) with a GPT partition table and two partitions inside it: one for
SWAP, the other one for the system and everyting else, formatted with Btrfs.

The laptop runs libreboot, so I have GRUB2 as a payload inside the flash chip
which I use to decrypt the LUKS container and load a GRUB configfile
located at /boot/grub/grub.cfg (generated by grub-mkconfig). This works fine.


While experimenting with GPT inside LUKS before the installation I've noticed
two issues, with at least one of them being present also after installation:

First, after unlocking the LUKS containter the two GPT partitions don't become
visible to the kernel automatically. I have to manually do
  partprobe /dev/mapper/<dmname>
to inform the kernel about the two new partitions. partprobe is part of parted.
My idea was to create a custom hook just after the 'encrypt' hook, which would
simply run the above command. I tested this and it seems to work.

Question:
Is there an even simpler solution to that problem? For example an alternative
to partprobe which is already in 'base'?


The second issue was that I could not (after unmounting the Btrfs partition and
deactivating the swap partition of course) directly close the LUKS mapping via
  cryptsetup luksClose <dmname>
It gave me:
  device-mapper: remove ioctl on <dmname> failed: Device or resource busy
  [...]
  device-mapper: remove ioctl on <dmname> failed: Device or resource busy
  Device <dmname> is still in use.

Instead, I had to remove the partition mappings first via
  dmsetup remove <dmname>1 <dmname>2
This was getting me rid of the aforementioned error messages.

As expected, I get these error messages also during system shutdown -- but only
whith the shutdown hook in initramfs. Without it, I presume the system does not
even try to close the LUKS container (which would make sense, since there is no
initramfs created by default for shutdown afaik), therefore also resulting in
no error messages being shown.

What could I do about this?
I'd like to have my system closing the LUKS container correctly -- therefore I
need to remove the partition mappings before that.


I've read a lot in the last days and weeks about Btrfs, SSDs, coreboot, etc. to
make sure I don't run into many issues. Though these two don't come unexpected,
I don't know how to solve the latter one, because systemd shutdown and shutdown
initramfs are still a little miracle to me...

I'd really appreciate any help!

This is all on an up-to-date vanilla 4.8.10-1-ARCH.
I attached two shutdown logs with debugging enabled: one with and one without
the shutdown hook applied. They look very similar though. (I made sure to reboot
twice after building the initramfs before taking the shutdown log.)
My HOOKS array is:
  HOOKS="base udev autodetect modconf block keyboard keymap encrypt pp \
  filesystems fsck shutdown"
(pp being the hook which runs partprobe against the mapped LUKS container)


Best Regards,

Merlin






























-- 
Merlin Büge <toni at bluenox07.de>
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