From 3067270c0c60ab10b803cb57f4b170f42913dd9b Mon Sep 17 00:00:00 2001
From: Andrew Cady <d@jerkface.net>
Date: Wed, 13 May 2020 18:45:37 -0400
Subject: split btrfs filesystem into two seed layers

---
 .gitignore |  5 +++++
 Makefile   | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++----
 2 files changed, 73 insertions(+), 4 deletions(-)

diff --git a/.gitignore b/.gitignore
index 697ef25..70a7dc0 100644
--- a/.gitignore
+++ b/.gitignore
@@ -42,3 +42,8 @@ samizdat.iso
 TEST_CHILD.*.log
 krng-add-entropy
 reused-child
+gold.iso
+patched.iso
+rootfs/samizdat.patch.btrfs
+rootfs/samizdat.seed.btrfs
+rootfs/seed.iso
diff --git a/Makefile b/Makefile
index c686735..03e748d 100644
--- a/Makefile
+++ b/Makefile
@@ -166,7 +166,72 @@ isotest-netinst: samizdat.netinst.iso
 gpg_iso_path=gnupghome
 GPG_INPUT_DIR=${samizdat_child_dir}/child.$(shell cat reused-child)/root/.gnupg
 
-samizdat.iso: rootfs/samizdat.iso reused-child
+samizdat_btrfs_patch_size=256M
+
+get_loop_dev="$$(sudo losetup -n -O name -j $@~tmp)"
+get_backing_file="$$(sudo losetup -n -O back-file -j $@~tmp)"
+get_min_size="$$(btrfs inspect-internal min-dev-size --id 1 $@.mnt | (read b _; echo $$b))"
+
+rootfs/samizdat.seed.btrfs: rootfs/samizdat.btrfs
+ifneq ($(shell id -u),0)
+	sudo make $@
+else
+	cp --reflink $< $@~tmp
+	btrfstune -f -S0 $@~tmp
+	test -d $@.mnt || mkdir $@.mnt
+	mount -t btrfs -o rw $@~tmp $@.mnt
+	btrfs fi defrag -c -r $@.mnt
+	s=$(get_min_size) && (set -x; btrfs fi resize 1:$$s $@.mnt && truncate -s "$$s" $@~tmp)
+	umount $@.mnt
+	losetup -f $<
+	btrfstune -S1 $@~tmp
+	mv $@~tmp $@
+endif
+
+rootfs/samizdat.patch.btrfs: rootfs/samizdat.seed.btrfs
+ifneq ($(shell id -u),0)
+	sudo make $@
+else
+	rm -f $@~tmp
+	touch $@~tmp
+	fallocate -l $(samizdat_btrfs_patch_size) $@~tmp
+	test -d $@.mnt || mkdir $@.mnt
+	! mountpoint -q $@.mnt || umount $@.mnt
+	mount -o ro -t btrfs $< $@.mnt
+	a=$(get_loop_dev); [ -z "$$a" ] || losetup -d $$a
+	losetup -f $@~tmp
+	btrfs device add $(get_loop_dev) $@.mnt
+	mount -o rw,remount $@.mnt
+	chroot $@.mnt /bin/sh -c 'echo samizdat > /etc/hostname'
+	chroot $@.mnt bash -i
+	umount $@.mnt
+	losetup -f $<
+	btrfstune -S1 $@~tmp
+	mv $@~tmp $@
+endif
+
+samizdat.iso: patched.iso
+	cp --reflink $< $@
+
+patched.iso: gold.iso rootfs/samizdat.patch.btrfs
+	rm -f $@~tmp
+	cp --reflink $< $@~tmp
+	sudo xorrisofs -iso-level 3 -- \
+		-indev $@~tmp \
+		-outdev $@~tmp \
+		-return_with FAILURE 32 \
+		-pathspecs on \
+		-follow link \
+		-add /rootfs/z00.btrfs=rootfs/samizdat.patch.btrfs -- \
+		-follow default \
+		-as mkisofs -graft-points \
+		-b grub/i386-pc/eltorito.img  \
+		-no-emul-boot -boot-info-table \
+		--embedded-boot "${samizdat_grub_efi_dir}"/embedded.img \
+		--protective-msdos-label
+	mv $@~tmp $@
+
+gold.iso: rootfs/seed.iso reused-child
 	sudo grub-efi.sh
 	! grep 'vmlinuz.*nbdroot' -r ${samizdat_grub_efi_dir}
 	rm -f $@~tmp
@@ -175,7 +240,6 @@ samizdat.iso: rootfs/samizdat.iso reused-child
 		-indev $@~tmp \
 		-outdev $@~tmp \
 		-return_with FAILURE 32 \
-		-volid SamizdatLive \
 		-pathspecs on \
 		-rm_r linux -- \
 		-add linux="${samizdat_linux_dir}" -- \
@@ -193,7 +257,7 @@ samizdat.iso: rootfs/samizdat.iso reused-child
 		--protective-msdos-label
 	mv $@~tmp $@
 
-rootfs/samizdat.iso: rootfs/samizdat.btrfs
+rootfs/seed.iso: rootfs/samizdat.seed.btrfs
 	rm -f $@~tmp
 	touch $@~tmp
 	fallocate -n -l 10G $@~tmp
@@ -204,7 +268,7 @@ rootfs/samizdat.iso: rootfs/samizdat.btrfs
 		-volid SamizdatLive \
 		-pathspecs on \
 		-follow link \
-		-add /rootfs/samizdat.btrfs=/srv/nbd/samizdat.btrfs -- \
+		-add /rootfs/samizdat.btrfs=$< -- \
 		-follow default
 	mv $@~tmp $@
 
-- 
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