pid1: initial "run as PID 1" feature

This one has been inspired by these guys: http://www.informatimago.com/linux/emacs-on-user-mode-linux.html https://raymii.org/s/blog/Vim_as_PID_1_Boot_to_Vim.html It's aimed at building images running their main userspace piece instead of ramdisk's init, that means PID=1, UID=0. Mostly fun of course but it suddenly became interesting with kernel IP autoconfiguration and e.g. elinks running this way (NB: requires patched make-initrd 0.8.8 at the moment to get resolver configured). And startup times are way better than sysvinit and systemd combined!

pid1: initial "run as PID 1" feature
1a7eed30 · Michael Shigorin · 6f452182 · 1a7eed30 · 1a7eed30 · 1a7eed30
Commit 1a7eed30 authored Sep 18, 2014 by Michael Shigorin
5 changed files
--- a/features.in/pid1/README
+++ b/features.in/pid1/README
+Эта экспериментальная фича предназначена для обеспечения запуска
+заданного приложения в моно^Wкачестве единственного, т.е. PID 1.
+
+Особенности результата:
+- предельно быстрый запуск;
+- работа под root;
+- отсутствие какой бы то ни было инициализации окружения.
+
+Возможна настройка сетевых интерфейсов средствами ядра, условия:
+- статически собранный модуль для используемого интерфейса;
+- доступность DHCP/BOOTP/RARP в сегменте локальной сети.
+
+Пакет следует добавить в STAGE1_PACKAGES; путь к бинарнику
+задаётся в PID1_BIN; PID1_PANIC позволяет указать время до
+перезагрузки ядра при завершении работы приложения.
--- a/features.in/pid1/config.mk
+++ b/features.in/pid1/config.mk
+# choose the smallest suitable kernel
+use/pid1: sub/stage1 use/syslinux/timeout/1
+	@$(call add_feature)
+	@$(call add,STAGE1_PACKAGES,make-initrd)
+	@$(call add,STAGE2_BOOTARGS,quiet)
+	@$(call add,STAGE2_BOOTARGS,panic=$$(PID1_PANIC))
+	@$(call add,STAGE2_BOOTARGS,rdinit=$$(PID1_BIN))
+	@$(call add,SYSLINUX_CFG,pid1)
+	@$(call try,PID1_PANIC,3)
+	@$(call xport,PID1_PANIC)
+	@$(call xport,PID1_BIN)
+ifeq (i586,$(ARCH))
+	@$(call set,KFLAVOURS,ltsp-client)
+endif
+
+# need a kernel with CONFIG_IP_PNP_DHCP
+# NB: make-initrd must support resolver setup!
+use/pid1/net: use/pid1
+	@$(call add,STAGE2_BOOTARGS,ip=dhcp)
+	@$(call add,STAGE1_PACKAGES,chrooted-resolv)
--- a/features.in/pid1/stage1/scripts.d/11-initrd-pid1
+++ b/features.in/pid1/stage1/scripts.d/11-initrd-pid1
+#!/bin/sh
+# vi's +builtin_terms only cover ansi/xterm
+
+echo "PUT_FILES += /lib/terminfo/l/linux $GLOBAL_PID1_BIN" >> /etc/initrd.mk
--- a/features.in/pid1/stage1/scripts.d/82-gzip-initfs
+++ b/features.in/pid1/stage1/scripts.d/82-gzip-initfs
+#!/bin/sh
+
+gzip < /boot/initrd.img > /boot/full.cz
--- a/features.in/syslinux/cfg.in/20pid1.cfg
+++ b/features.in/syslinux/cfg.in/20pid1.cfg
+label pid1
+  menu label ^Just run as PID 1
+  kernel alt0/vmlinuz
+  append initrd=alt0/full.cz @bootargs@