feat: add MontaukOS Imager tool for Raspberry Pi

GNUmakefile

@@ -429,6 +429,12 @@ ifneq ($(ARCH),aarch64)
 endif
 	./scripts/mk-rpi4-sd.sh kernel/bin-$(ARCH)/kernel ramdisk.tar $@ $(ROOTFS) $(PROGRAMS_BIN)-rpi
 
+# Graphical imager: write montauk-rpi4.img to an SD card, or update the
+# installation on one in place (scripts/montauk-imager.py, docs/raspberry-pi.md).
+.PHONY: rpi4-imager
+rpi4-imager:
+	./scripts/montauk-imager.py
+
 $(IMAGE_NAME).hdd: limine/limine kernel ramdisk
 	rm -f $(IMAGE_NAME).hdd
 	dd if=/dev/zero bs=1M count=0 seek=64 of=$(IMAGE_NAME).hdd

docs/raspberry-pi.md

@@ -12,6 +12,50 @@ make ARCH=aarch64 rpi4-sd                        # -> montauk-rpi4.img
 sudo dd if=montauk-rpi4.img of=/dev/sdX bs=4M conv=fsync
 ```
 
+Or use the imager, which also updates a card in place:
+
+```bash
+make rpi4-imager                                 # = ./scripts/montauk-imager.py
+```
+
+### The imager
+
+`scripts/montauk-imager.py` is a Tk window (`python3-tk`) that lists the SD
+cards and USB drives attached (never the host's own disks) and what is on
+them, and either writes a fresh image or updates the MontaukOS on a card. It
+runs as the user and does the writing by starting itself again through
+`pkexec` (it asks for the password each time). The same operations work from
+a terminal: `list`, and as root `flash`, `update` and `expand`
+(`--help` for the options). Images can be raw or `.gz`, `.xz` or `.zip`
+compressed; **Build** runs `make ARCH=aarch64 rpi4-sd`.
+
+- **Write a fresh image** erases the card, writes the image, clears the last
+  MiB of the card (a backup GPT from an earlier OS) and reads the card back to
+  verify it. *Expand* grows the root to fill the card right away instead of
+  leaving it to `firstboot.elf`.
+- **Update** leaves the partition table alone and finds both partitions by
+  label, so a root that has grown to fill the card (or was resized by hand)
+  stays as it is. On the ESP every file is written except `RPI_EFI.fd`, which
+  holds the firmware's own settings (*Update the UEFI firmware* replaces it);
+  a changed `config.txt` is kept as `config.txt.bak`. On the root, `os/`,
+  `apps/`, `sdk/`, `boot/` get the image's new and changed files; `config/`
+  and `www/` only get files the card lacks, `users/` and `state/` are not
+  touched. `init.toml` becomes the image's, keeping each service's `enabled`
+  from the card and appending services only the card has; `capabilities.toml`
+  becomes the image's plus grants only the card has (old copies: `.old`).
+  `os/firstboot.elf` is only written if the card still has it, so a grown
+  card does not grow again. *Remove system files the new image no longer
+  ships* prunes `os/`, `apps/`, `sdk/` and `boot/` (keeping `os/btkeys.bin`,
+  the Bluetooth bonds). Unchanged files are skipped and each file is
+  replaced by a rename; the volume is checked with `e2fsck` before and after,
+  and its features against what `Fs/Ext2.cpp` mounts.
+- **Expand** (a host-side first boot) grows the root partition to the end of
+  the card, at most 1 TiB, and the volume with `resize2fs`; `firstboot.elf`
+  then finds nothing to do and deletes itself.
+
+While it works, a runtime udev rule keeps the desktop from automounting the
+card's partitions (Linux writes to an ext2 volume as soon as it mounts it).
+
 `scripts/mk-rpi4-sd.sh` downloads the firmware release once into
 `rpi4-firmware/` (`PFTF_VERSION=v1.53` by default) and builds an MBR image: