Re: [arch-general] Kpartx should be in the repos and archiso for enabling encrypted GPT install

14 Jan 2019

      On Sun, 13 Jan 2019 08:56:55 -0800 (PST)
Neven Sajko via arch-general <arch-general@archlinux.org> wrote:
...
To mount a root GPT partition which resides on an encrypted disk, one
needs the kpartx tool to make the mapping for the partition (the
kernel does not independently make those for partitions on device
mapper maps, which is what a dm-crypt decrypted device is). Thus
kpartx needs to be on the Archlinux installation ISO to enable that
kind of setup.
Hi,

I'm not sure this is applicable to your setup (I'm tired right now but
skimmed the hole thread), but I'm using a root GPT inside a LUKS
container. To make the kernel aware of the partitions at boot, I run
partprobe (part of parted) on the opened LUKS mapping device:

$ cat /etc/initcpio/install/partprobe 
#!/bin/bash

build() {
    add_binary partprobe
    add_runscript
}

help() {
    cat <<HELPEOF
This custom hook scans a mapped LUKS container for GPT partitions and
informs the OS kernel about them.
HELPEOF
}

$ cat /etc/initcpio/hooks/partprobe 
#!/usr/bin/ash

run_hook() {
    partprobe /dev/mapper/matrix_vol
}

Works fine for me. Sorry if I'm missing the point here.

Kind Regards,

Merlin
...
It would of course first be necessary for an Archlinux Developer or
Trusted User to adopt kpartx, so I hope there is somebody willing to
do this ...? Note that kpartx is a common utility and in its own
package across a lot of distributions; like Debian, Ubuntu, Fedora,
OpenSUSE, ...
Note: it may be possible to use losetup instead of kpartx so as to
make a loop device instead of a device map, but that would come with
an overhead? Another alternative setup, perhaps more widely used, is
having encrypted LVM. While this does not require kpartx, LVM may be
undesireable because of its complexity and requiring multiple
userspace daemons beside Udev.
Appended is an example PKGBUILD which only installs the kpartx
executable and manual page:
pkgname=(kpartx)
pkgver=0.7.9
pkgrel=1
pkgdesc='Create device mapper maps for partitions in devices or files'
arch=(x86_64)
url='http://christophe.varoqui.free.fr'
license=(LGPL GPL GPL2)
depends=(device-mapper)
makedepends=(gzip)
source=('mpt.tar.gz::https://git.opensvc.com/?p=multipath-tools/.git;a=snapshot;h=5c67a8b5944dd13...')
md5sums=()
sha512sums=('d4abc9580b6a3e457c99bee96d5aaab29a984ae77f91cbbe52e1b4af16809319a9100c45ce5600242fa52819dd44a9cb77e13305bc4f9651c532906243f2d544')
build() {
  cd multipath-tools-5c67a8b/kpartx
  gcc -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64
-DLIBDM_API_COOKIE -l devmapper -o kpartx $CPPFLAGS $CFLAGS $LDFLAGS
*.c gzip kpartx.8 }
package() {
  cd multipath-tools-5c67a8b/kpartx
  install -d "$pkgdir/usr/bin"
  install -m 755 kpartx "$pkgdir/usr/bin"
  install -d "$pkgdir/usr/share/man/man8"
  install -m 644 kpartx.8.gz "$pkgdir/usr/share/man/man8"
}
-- 
Merlin Büge