copy "how to flash" from the old docs

doc/admin.rst

@@ -1,15 +1,188 @@
 System Administration
 #####################
 
-..
+Services on a running system
-     - administration guide
+****************************
 
-       - what you can do on a running system
+* add an s6-rc cheatsheet here
-	  - s6-rc commands
 
-       - writable filesystem: min-copy-closure, min-collect-garbage,
-	 liminix-rebuild
 
-       - full flash:
+Flashing and updating
-	 how to do the two-step thing
+*********************
-	 flash from OpenWrt
+
+
+
+Flashing from an existing Liminix system with :command:`flashcp`
+================================================================
+
+The flash procedure from an existing Liminix-system has two steps.
+First we reboot the device (using "kexec") into an "ephemeral"
+RAM-based version of the new configuration, then when we're happy it
+works we can flash the image - and if it doesn't work we can reboot
+the device again and it will boot from the old image.
+
+
+Building the RAM-based image
+----------------------------
+
+To create the ephemeral image, build ``outputs.kexecboot`` instead of
+``outputs.default``.  This generates a directory containing the root
+filesystem image and kernel, along with an executable called `kexec`
+and a `boot.sh` script that runs it with appropriate arguments.
+
+For example
+
+.. code-block:: console
+
+   nix-build --show-trace -I liminix-config=./examples/arhcive.nix \
+     --arg device "import ./devices/gl-ar750"
+     -A outputs.kexecboot && \
+     (tar chf - result | ssh root@the-device tar -C /run -xvf -)
+
+and then login to the device and run
+
+.. code-block:: console
+
+   cd /run/result
+   sh ./boot.sh .
+
+
+This will load the new kernel and map the root filesystem into a RAM
+disk, then start executing the new kernel. *This is effectively a
+reboot - be sure to close all open files and finish anything else
+you were doing first.*
+
+If the new system crashes or is rebooted, then the device will revert
+to the old configuration it finds in flash.
+
+
+Building the second (permanent) image
+-------------------------------------
+
+While running in the kexecboot system, you can copy the permanent
+image to the device with :command:`ssh`
+
+.. code-block:: console
+
+   build-machine$ tar chf - result/firmware.bin | \
+    ssh root@the-device tar -C /run -xvf -
+
+Next you need to connect to the device and locate the "firmware"
+partition, which you can do with a combination of :command:`dmesg`
+output and the contents of :file:`/proc/mtd`
+
+.. code-block:: console
+
+   <5>[    0.469841] Creating 4 MTD partitions on "spi0.0":
+   <5>[    0.474837] 0x000000000000-0x000000040000 : "u-boot"
+   <5>[    0.480796] 0x000000040000-0x000000050000 : "u-boot-env"
+   <5>[    0.487056] 0x000000050000-0x000000060000 : "art"
+   <5>[    0.492753] 0x000000060000-0x000001000000 : "firmware"
+
+   # cat /proc/mtd
+   dev:    size   erasesize  name
+   mtd0: 00040000 00001000 "u-boot"
+   mtd1: 00010000 00001000 "u-boot-env"
+   mtd2: 00010000 00001000 "art"
+   mtd3: 00fa0000 00001000 "firmware"
+   mtd4: 002a0000 00001000 "kernel"
+   mtd5: 00d00000 00001000 "rootfs"
+
+Now run (in this example)
+
+.. code-block:: console
+
+   flashcp -v firmware.bin /dev/mtd3
+
+
+"I know my new image is good, can I skip the intermediate step?"
+----------------------------------------------------------------
+
+In addition to giving you a chance to see if the new image works, this
+two-step process ensures that you're not copying the new image over
+the top of the active root filesystem. Sometimes it works, but you
+will at least need physical access to the device to power-cycle it
+because it will be effectively frozen afterwards.
+
+
+Flashing from the boot monitor
+==============================
+
+If you are prepared to open the device and have a TTL serial adaptor
+of some kind to connect it to, you can probably flash it using U-Boot.
+This is quite hardware-specific, and sometimes involves soldering:
+please refer to the Developer Manual.
+
+
+Flashing from OpenWrt (not currently advised!)
+==============================================
+
+.. CAUTION:: At your own risk! This will (at least in some
+             circumstances) lead to bricking the device: we think this
+             flash method is currently incompatible with use of a
+             writeable (jffs2) filesystem.
+
+If your device is running OpenWrt then it probably has the
+:command:`mtd` command installed. After transferring the image onto the
+device using e.g. :command:`ssh`,  you can run it as follows:
+
+.. code-block:: console
+
+   mtd -r write /tmp/firmware.bin firmware
+
+For more information, please see the `OpenWrt manual <https://openwrt.org/docs/guide-user/installation/sysupgrade.cli>`_ which may also contain (hardware-dependent) instructions on how to flash an image using the vendor firmware - perhaps even from a web interface.
+
+Updating an installed system (JFFS2)
+************************************
+
+
+Adding packages
+===============
+
+If your device is running a JFFS2 root filesystem, you can build
+extra packages for it on your build system and copy them to the
+device: any package in Nixpkgs or in the Liminix overlay is available
+with the ``pkgs`` prefix:
+
+.. code-block:: console
+
+    nix-build -I liminix-config=./my-configuration.nix \
+     --arg device "import ./devices/mydevice" -A pkgs.tcpdump
+
+    nix-shell -p min-copy-closure root@the-device result/
+
+Note that this only copies the package to the device: it doesn't update
+any profile to add it to ``$PATH``
+
+
+Rebuilding the system
+=====================
+
+:command:`liminix-rebuild` is the Liminix analogue of :command:`nixos-rebuild`, although its operation is a bit different because it expects to run on a build machine and then copy to the host device. Run it with the same ``liminix-config`` and ``device`` parameters as you would run :command:`nix-build`, and it will build any new/changed packages and then copy them to the device using SSH. For example:
+
+.. code-block:: console
+
+     liminix-rebuild root@the-device  -I liminix-config=./examples/rotuer.nix --arg device "import ./devices/gl-ar750"
+
+This will
+
+* build anything that needs building
+* copy new or changed packages to the device
+* reboot the device
+
+It doesn't delete old packages automatically: to do that run
+:command:`min-collect-garbage`, which will delete any packages not in
+the current system closure. Note that Liminix does not have the NixOS
+concept of environments or generations, and there is no way back from
+this except for building the previous configuration again.
+
+
+Caveats
+~~~~~~~
+
+* it needs there to be enough free space on the device for all the new
+  packages in addition to all the packages already on it - which may be
+  a problem if a lot of things have changed (e.g. a new version of
+  nixpkgs).
+
+* it cannot upgrade the kernel, only userland

doc/configuration.rst

@@ -1,5 +1,5 @@
-Configuration and Module Guide
+Configuration
-##############################
+#############
 
 Liminix uses the Nix language to provide congruent configuration
 management.  This means that to change anything about the way in
@@ -150,8 +150,7 @@ meaning that it won't be started until that other service is up.
 Module implementation
 *********************
 
-..
+TODO: make your own modules
-	TODO: make your own modules
 
-	* how a module exposes services
+* how a module exposes services
-	* defining types
+* defining types