01/01: website: Add post about porting GuixSD to ARMv7.

[Mathieu Othacehe]

mothacehe pushed a commit to branch master
in repository guix-artwork.

commit ccb9fb1456f9f5b9f4fb4f8365c60e016e52c1bf
Author: Mathieu Othacehe <address@hidden>
Date:   Fri Dec 22 12:04:10 2017 +0100

    website: Add post about porting GuixSD to ARMv7.
    
    * website/posts/guixsd-port-arm.md: New file.
    * website/static/blog/img/guixsd-bbb1.jpg: New file.
---
 website/posts/guixsd-port-arm.md        | 224 ++++++++++++++++++++++++++++++++
 website/static/blog/img/guixsd-bbb1.jpg | Bin 0 -> 152633 bytes
 2 files changed, 224 insertions(+)

diff --git a/website/posts/guixsd-port-arm.md b/website/posts/guixsd-port-arm.md
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+title: Porting GuixSD to ARMv7
+date: 2017-12-22 11:00
+author: Mathieu Othacehe
+tags: GuixSD, ARM, BeagleBone Black.
+---
+
+GuixSD porting to ARMv7 is a difficult topic. There are plenty of
+different machines, with specific hardware configurations and
+vendor-tuned bootloaders, and ACPI support is still experimental. For
+those reasons it is currently impossible to provide a GuixSD image
+that runs on most ARMv7 machines like on x86_64 targets.
+
+The GuixSD port on ARMv7 has to be done machine by machine and the
+first supported one is the BeagleBone Black. It was choosen mainly
+because it runs with mainline U-Boot and Linux-libre kernel.
+
+As Guix already supported armv7, only three things were missing:
+
+1. A rework of the GuixSD bootloader layer to support not just GRUB but
+also U-Boot and Extlinux. This has been integrated in the [0.14
+release](https://www.gnu.org/software/guix/blog/2017/gnu-guix-and-guixsd-0.14.0-released/).
+2. Some developments and fixes on Guix scripts to support image generation,
+system reconfiguration and installation on ARMv7 in the same way as it is
+already possible on i686 and x86_64 machines.
+3. The definition on an installation image for the BeagleBone Black.
+
+Points 2 and 3 were addressed recently so we are now ready to show you
+how to run GuixSD on your BeagleBone Black board!
+
+#### Installing GuixSD on a BeagleBone Black
+
+Let's try to install GuixSD on the 4GB eMMC (built-in flash memory) of
+a BeagleBone Black.
+
+Future Guix releases will provide pre-built installer images for the
+BeagleBone Black. For now, as support just landed on "master", we need
+to build this image by ourselves.
+
+This can be done this way:
+
+```
+guix system disk-image --system=armhf-linux -e "(@ (gnu system install) 
beaglebone-black-installation-os)"
+```
+
+Note that it is not yet possible to cross-compile a disk image. So you
+will have to either run this command on an armhf-linux system where
+you have previously installed Guix manually, or offload the build to such a
+system.
+
+You will eventually get something like:
+
+```
+installing bootloader...
+[ 7710.782381] reboot: Restarting system
+/gnu/store/v33ccp7232gj5wdahdgpjcw4nvh14d7s-disk-image
+```
+
+Congrats! Let's flash this image onto a microSD card with the command:
+
+```
+dd if=/gnu/store/v33ccp7232gj5wdahdgpjcw4nvh14d7s-disk-image of=/dev/mmcblkX 
bs=4M
+```
+where mmcblkX is the name of your microSD card on your GNU/Linux machine.
+
+You can now insert the microSD card into you BeagleBone Black, plug in a
+UART cable and power-on your device while pressing the "S2" button to
+force the boot from microSD instead of eMMC.
+
+![GuixSD installer on BeagleBone Black](/static/blog/img/guixsd-bbb1.jpg)
+
+Let's follow the [Guix documentation
+here](https://www.gnu.org/software/guix/manual/html_node/Preparing-for-Installation.html#Preparing-for-Installation)
+to install GuixSD on eMMC.
+
+First of all, let's plug in an ethernet cable and set up SSH access in order to
+be able to get rid of the UART cable.
+
+```
+ifconfig eth0 up
+dhclient eth0
+herd start ssh-daemon
+```
+
+Let's partition the eMMC (/dev/mmcblk1) as a 4GB ext4 partition,
+mount it, and launch the cow-store service, still following the
+documentation.
+
+```
+cfdisk
+mkfs.ext4 -L my-root /dev/mmcblk1p1
+mount LABEL=my-root /mnt
+herd start cow-store /mnt
+```
+
+We have reached the most important part of this whole process. It is now
+time to write the configuration file of our new system.
+The best thing to do here is to start from the template
+`beaglebone-black.scm`:
+
+```
+mkdir /mnt/etc
+cp /etc/configuration/beaglebone-black.scm /mnt/etc/config.scm
+zile /mnt/etc/config.scm
+```
+
+Once you are done preparing the configuration file, the new system must be 
initialized
+with this command:
+
+```
+guix system init /mnt/etc/config.scm /mnt
+```
+
+When this is over, you can turn off the board and remove the microSD card. 
When you'll
+power it on again, it will boot a bleeding edge GuixSD---isn't that nice?
+
+#### Preparing a dedicated system configuration
+
+Installing GuixSD on eMMC is great but you can also use Guix
+to prepare a portable microSD card image for your favorite server 
configuration. Say
+you want to run an mpd server on a BeagleBone Black directly from microSD card,
+with a minimum of configuration steps.
+
+The system configuration could look like this:
+
+```scheme
+(use-modules (gnu) (gnu bootloader extlinux))
+(use-service-modules audio networking ssh)
+(use-package-modules screen ssh)
+
+(operating-system
+  (host-name "my-mpd-server")
+  (timezone "Europe/Berlin")
+  (locale "en_US.utf8")
+  (bootloader (bootloader-configuration
+               (bootloader u-boot-beaglebone-black-bootloader)
+               (target "/dev/sda")))
+  (initrd (lambda (fs . rest)
+            (apply base-initrd fs
+                   ;; This module is required to mount the sd card.
+                   #:extra-modules (list "omap_hsmmc")
+                   rest)))
+  (file-systems (cons (file-system
+                        (device "my-root")
+                        (title 'label)
+                        (mount-point "/")
+                        (type "ext4"))
+                      %base-file-systems))
+  (users (cons (user-account
+                (name "mpd")
+                (group "users")
+                (home-directory "/home/mpd"))
+               %base-user-accounts))
+  (services (cons* (dhcp-client-service)
+                   (service mpd-service-type)
+                   (agetty-service
+                    (agetty-configuration
+                     (extra-options '("-L"))
+                     (baud-rate "115200")
+                     (term "vt100")
+                     (tty "ttyO0")))
+                   %base-services)))
+```
+After writing this configuration to a file called `mpd.conf`, it's possible to
+forge a disk image from it, with the following command:
+
+```
+guix system disk-image --system=armhf-linux mpd.conf
+```
+
+Like in the previous section, the resulting image should be copied to a 
microSD card.
+Then, booting from it on the BeagleBone Black, you should get:
+
+```
+...
+Service mpd has been started.
+This is the GNU system.  Welcome.
+my-mpd-server login:
+```
+
+With only two commands you can build a system image from a configuration file, 
flash it
+and run it on a BeagleBone Black!
+
+#### Next steps
+
+* Porting GuixSD to other ARMv7 machines.
+
+While most of the work for supporting ARMv7 machines is done, there's
+still work left to create specific installers for other machines.
+This mostly consists of specifying the right bootloader and initrd
+options, and testing the whole thing.
+
+One of the next supported systems might be the
+[EOMA68-A20](https://www.crowdsupply.com/eoma68/micro-desktop) as we
+should get a pre-production unit soon.  Feel free to add
+support for your favorite machine!
+
+This topic will be discussed in a future post.
+
+* Allow system cross-compilation.
+
+This will be an interesting feature to allow producing a disk image from
+a desktop machine on x86_64 for instance. More development work is needed,
+but we'll keep you informed.
+
+#### About GNU Guix
+
+[GNU Guix](https://www.gnu.org/software/guix) is a transactional package
+manager for the GNU system.  The Guix System Distribution or GuixSD is
+an advanced distribution of the GNU system that relies on GNU Guix and
+[respects the user's
+freedom](https://www.gnu.org/distros/free-system-distribution-guidelines.html).
+
+In addition to standard package management features, Guix supports
+transactional upgrades and roll-backs, unprivileged package management,
+per-user profiles, and garbage collection.  Guix uses low-level
+mechanisms from the Nix package manager, except that packages are
+defined as native [Guile](https://www.gnu.org/software/guile) modules,
+using extensions to the [Scheme](http://schemers.org) language.  GuixSD
+offers a declarative approach to operating system configuration
+management, and is highly customizable and hackable.
+
+GuixSD can be used on an i686, x86_64 and armv7 machines.  It is also
+possible to use Guix on top of an already installed GNU/Linux system,
+including on mips64el and aarch64.
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