From bd12fb780733b6bdc08fcc47b9e50742a9d77b43 Mon Sep 17 00:00:00 2001
From: Diederik de Haas <github@cknow.org>
Date: Sat, 17 Jul 2021 16:07:21 +0200
Subject: [PATCH] Implement workaround for low-mem models.

The installer makes a backup (in memory) of itself to /bootfs, but after
restore to the new FAT32 partition doesn't remove that memory copy.
The 256MB model is so memory constrained that it fails, likely due to
an OOM problem. For those models (only), remove the RAM copy and when
the new boot partition gets mounted (to /rootfs/boot), make a
'mount --bind' to /bootfs, so for all intend and purposes the rest
should still work the same.

Signed-off-by: Diederik de Haas <github@cknow.org>
---
 scripts/etc/init.d/rcS | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/scripts/etc/init.d/rcS b/scripts/etc/init.d/rcS
index b4b64e49..9a5c7b97 100755
--- a/scripts/etc/init.d/rcS
+++ b/scripts/etc/init.d/rcS
@@ -1119,6 +1119,25 @@ sync
 umount /boot || fail
 log_msg_end "OK"
 
+model_memory=$(busybox free -m | grep "^Mem:" | awk '{print $2}')
+low_mem_model=""
+if [ "$model_memory" -le "260" ] ; then
+    low_mem_model="true"
+else
+    low_mem_model="false"
+fi
+log_msg "Model memory in MB: '$model_memory' is a low mem model: '$low_mem_model'"
+
+if [ "$low_mem_model" = "true" ] ; then
+    log_msg_start "Removing backup copy in /bootfs... "
+    rm -r -- /bootfs/*
+    log_msg_end "OK"
+else
+    log_msg "Keeping backup copy in /bootfs"
+fi
+
+print_mem_info
+
 # only do modprobe if the module is NOT built into the kernel
 if [ "$(grep -c $rootfstype /lib/modules/"$(uname -r)"/modules.builtin)" -eq 0 ]; then
     log_msg_start "Loading $rootfstype module... "
@@ -1137,6 +1156,12 @@ mkdir /rootfs/boot || fail
 mount $bootpartition /rootfs/boot || fail
 log_msg_end "OK"
 
+if [ "$low_mem_model" = "true" ] ; then
+    log_msg_start "Bind mount /rootfs/boot to /bootfs... "
+    mount --bind /rootfs/boot /bootfs
+    log_msg_end "OK"
+fi
+
 print_mem_info
 
 log_msg "Starting install process..."
@@ -1694,6 +1719,11 @@ chmod 0640 /rootfs/var/log/raspbian-ua-netinst.log
 
 log_msg_start "Unmounting filesystems... "
 
+if [ "$low_mem_model" = "true" ] ; then
+    log_msg_inline "removing bind mount to /bootfs... "
+    umount /bootfs
+fi
+
 umount /rootfs/boot
 umount /rootfs
 log_msg_end "OK"