Execute some code at boot made accessible to the VM by mounting a disk

.gitignore

@@ -1,2 +1,4 @@
 /*.nar
-/signing-key.pub
+/*.sizes
+/signing-key.pub
+/vm-image

Makefile

@@ -1,24 +1,31 @@
 tmp_image := $(shell echo $$$$)
 
-all: hello.nar signing-key.pub vm-image Makefile
+all: hello.nar hello.sizes signing-key.pub vm-image Makefile
 	qemu-img create -f qcow2 -o backing_file=vm-image vm-image-${tmp_image}
 # TODO: qcow2: make a derived image.
 	qemu-system-x86_64 -enable-kvm -m 256 \
 	  vm-image-${tmp_image} \
-	  -drive format=raw,readonly,file=hello.nar,index=0,if=ide,index=1,media=cdrom \
-	  -drive format=raw,readonly,file=signing-key.pub,index=0,if=ide,index=2,media=cdrom
+	  -drive format=raw,file=hello.sizes,if=ide,index=1,media=disk \
+	  -drive format=raw,file=to-be-run-in-vm.sh,if=ide,index=2,media=disk \
+	  -drive format=raw,file=hello.nar,if=ide,index=3,media=disk \
+	  # -drive format=raw,file=signing-key.pub,if=ide,index=4,media=disk
 	rm vm-image-${tmp_image}
 
+%.sizes: %.nar signing-key.pub Makefile
+	printf "%020d\\n%020d\\n%020d\\n%$$((512-((20+1)*3)-1))s\\n" \
+	  "$$(wc -c "to-be-run-in-vm.sh" | sed -e 's/^[[:space:]]*\([0-9][0-9]*\)[[:space:]].*$$/\1/')" \
+	  "$$(wc -c "$*.nar" | sed -e 's/^[[:space:]]*\([0-9][0-9]*\)[[:space:]].*$$/\1/')" \
+	  "$$(wc -c "signing-key.pub" | sed -e 's/^[[:space:]]*\([0-9][0-9]*\)[[:space:]].*$$/\1/')" \
+	  "" \
+	  > $@
+
 %.nar: Makefile
-	guix archive --export --recursive $* > $@
+	guix archive --export --recursive '$*' > '$@'
 
 signing-key.pub: /etc/guix/signing-key.pub Makefile
-	cp $< $@
-	chmod +w $@
+	cp '$<' '$@'
+	chmod +w '$@'
 
-.PHONY: rebuild
-rebuild: config.scm Makefile
-	ln -s "$$(guix system vm-image config.scm)" vm-image
-
-vm-image: config.scm # Makefile
-	ln -s "$$(guix system vm-image config.scm)" vm-image
+vm-image: config.scm Makefile
+	rm -f '$@'
+	ln -sf "$$(guix system vm-image config.scm)" '$@'

config.scm

@@ -1,12 +1,15 @@
 (use-modules (gnu)
              (gnu services shepherd))
 
-(define (my-service)
-  (shepherd-service
-   (documentation "This command is executed when the GUIX system boots.")
-   (provision '(my-stuff))
-   (start #~(lambda ()
-              (system* "seq 1000")))))
+(define my-service
+  (shepherd-service-type
+   'run-commands-at-boot
+   (lambda (x)
+     (shepherd-service
+      (documentation "This command is executed when the GUIX system boots.")
+      (provision '(my-stuff))
+      (start #~(lambda ()
+                 (system "(read len < /dev/sdb; dd if=/dev/sdc bs=1 count=$len | sh) > /dev/tty1")))))))
 
 (operating-system
  (bootloader
@@ -20,6 +23,6 @@
          (mount-point "/")
          (type "ext4"))
         %base-file-systems))
- (services (cons (my-service)
+ (services (cons (service my-service 42)
                  %base-services))
  (timezone "GMT"))

to-be-run-in-vm.sh

@@ -0,0 +1,9 @@
+#!/bin/sh
+
+echo LALALA
+{ read len_script; read len_nar; read len_key; } < /dev/sdb
+echo x $len_script y $len_nar z $len_key t
+head -c "$len_nar" /dev/sdd | sha1sum
+echo DONE
+# dd if=/dev/sde bs=1 count=$len_key | sha1sum
+#