From 95850a44c2fd911c2a7f86b82b8ad577e68a31f4 Mon Sep 17 00:00:00 2001
From: Raito Bezarius <masterancpp@gmail.com>
Date: Sat, 7 Sep 2024 22:28:05 +0200
Subject: [PATCH] feat(recovery): implement failsafe boot

for TFTP or anything, really.

Signed-off-by: Raito Bezarius <masterancpp@gmail.com>
---
 modules/outputs/initramfs.nix | 25 +++++++++++++++++++++++--
 pkgs/preinit/preinit.c        | 10 ++++++++++
 2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/modules/outputs/initramfs.nix b/modules/outputs/initramfs.nix
index 89d017f..c666c77 100644
--- a/modules/outputs/initramfs.nix
+++ b/modules/outputs/initramfs.nix
@@ -41,17 +41,38 @@ in
 
     system.outputs = {
       initramfs =
-        let inherit (pkgs.pkgsBuildBuild) gen_init_cpio;
+        let
+          inherit (pkgs.pkgsBuildBuild) gen_init_cpio cpio writeScript;
+          inherit (pkgs) busybox;
+          failsafe-init = writeScript "init" ''
+            #!/bin/sh
+            exec >/dev/console
+            echo Running in initramfs
+            PATH=${busybox}/bin:$PATH
+            export PATH
+            mount -t proc none /proc
+            mount -t sysfs none /sys
+            ${busybox}/bin/sh
+          '';
+          refs = pkgs.writeReferencesToFile busybox;
         in runCommand "initramfs.cpio" {} ''
-          cat << SPECIALS | ${gen_init_cpio}/bin/gen_init_cpio /dev/stdin > $out
+          cat << SPECIALS | ${gen_init_cpio}/bin/gen_init_cpio /dev/stdin > out
           dir /proc 0755 0 0
           dir /dev 0755 0 0
           nod /dev/console 0600 0 0 c 5 1
           dir /target 0755 0 0
           dir /target/persist 0755 0 0
           dir /target/nix 0755 0 0
+          dir /nix 0755 0 0
+          dir /nix/store 0755 0 0
+          dir /bin 0755 0 0
+          file /bin/sh  ${busybox}/bin/sh 0755 0 0
           file /init ${pkgs.preinit}/bin/preinit 0755 0 0
+          file /failsafe-init ${failsafe-init} 0755 0 0
           SPECIALS
+
+          find $(cat ${refs}) | ${cpio}/bin/cpio -H newc -o -A -v -O out
+          mv out $out
         '';
       systemConfiguration =
         pkgs.systemconfig config.filesystem.contents;
diff --git a/pkgs/preinit/preinit.c b/pkgs/preinit/preinit.c
index 7dd896b..4b5f3f1 100644
--- a/pkgs/preinit/preinit.c
+++ b/pkgs/preinit/preinit.c
@@ -98,6 +98,7 @@ int main(int argc, char *argv[], char *envp[])
 	    AVER(mount(opts.device, "/target/persist", opts.fstype, 0, opts.mount_opts));
 	} else {
 	    if(mount(opts.device, "/target/persist", opts.fstype, 0, opts.mount_opts) < 0) {
+		ERR("failed to mount primary device, mount the alternative device\n");
 		AVER(mount(opts.altdevice, "/target/persist", opts.fstype, 0, opts.mount_opts));
 	    }
 	}
@@ -118,5 +119,14 @@ int main(int argc, char *argv[], char *envp[])
 
 	AVER(execve("/persist/init", argv, envp));
     }
+
+    ERR("failed to mount the rootfs\n");
+    ERR("final stand using the failsafe initialization method\n");
+    ERR("the boot process is manual from now on\n");
+
+    argv[0] = "init";
+    argv[1] = NULL;
+    AVER(execve("/failsafe-init", argv, envp));
+
     die();
 }