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

[nsajko at gmail.com]

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.

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=5c67a8b5944dd13542e6b44fa2ae9803e0cc4282;sf=tgz')
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"
}