Added support for overlayfs backed on persistent device (e.g. USB key)

- Bumped new micro release
- Modified 'overlayroot into 'overlayroot=<device>' where <device>='tmpfs' or a real device (can also be specified by tag)
- Fixed a typo in 'overlayroot-motd.sh'
- Added code to resynchronize the lower on boot when a 'overlayroot.resync' file is present in upper

Signed-off-by: Renaud Métrich <renaud.metrich@laposte.net>

90-overlayroot.hook

@@ -0,0 +1,10 @@
+[Trigger]
+Type = File
+Operation = Install
+Operation = Upgrade
+Target = usr/lib/initcpio/*
+
+[Action]
+Description = Updating overlayroot initcpios...
+When = PostTransaction
+Exec = /usr/bin/mkinitcpio -p overlayroot

PKGBUILD

@@ -1,6 +1,6 @@
 pkgname=overlayroot
 pkgver=0.2
-pkgrel=1
+pkgrel=2
 pkgdesc="overlayFS root file system"
 arch=('any')
 url="https://github.com/nils-werner/arch-overlayroot"
@@ -9,24 +9,36 @@ depends=(
   'mkinitcpio'
   'arch-install-scripts'
 )
-install=overlayroot.install
 source=(
-  'overlayroot.install'
   'initcpio-install-overlayroot'
   'initcpio-hooks-overlayroot'
   'rwrootfs'
   'fsck.overlay'
   'journald-volatile-storage.conf'
   'overlayroot-motd.sh'
+  'mkinitcpio-overlayroot.conf'
+  'mkinitcpio-overlayroot.preset'
+  '90-overlayroot.hook'
 )
 sha256sums=(
-  'SKIP'
-  'SKIP'
-  'SKIP'
-  'SKIP'
-  'SKIP'
-  'SKIP'
-  'SKIP'
+  # 'initcpio-install-overlayroot'
+  '3f197246d31439c84d7433609628126354c02bc496b72291cf884a21d1e1d492'
+  # 'initcpio-hooks-overlayroot'
+  'ad262726508954ba51d821449cd03d2cb58ff181ea437fa0a229e3aeef675ee4'
+  # 'rwrootfs'
+  '75b8c2ebe9e08e58f207a82aa93cfdd0b46a2255e49493cf6fedfe97cc61bd98'
+  # 'fsck.overlay'
+  'e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855'
+  # 'journald-volatile-storage.conf'
+  'c0c9a711f7554fdd02650409b098fc0636b8f3f574f03d927c6df84f5ec82a7f'
+  # 'overlayroot-motd.sh'
+  'e2e917ab85d44abfc8e4c504cd8925d6fec5d26c452198303e2238464552e9a1'
+  # 'mkinitcpio-overlayroot.conf'
+  '0954c40ee94824707ed0d4bf65bda0be1b3e57c52dd8cd2d12df23bf597ae6a2'
+  # 'mkinitcpio-overlayroot.preset'
+  '7ebdad6c610b8d35dab94343b7a98fb7dca4534aa43c49680b346919496fd1e8'
+  # '90-overlayroot.hook'
+  '7ef79bcdbb7a4a340893ab40755a8f90c745d00396bee2f218cc8f78374aec19'
 )
 
 build() {
@@ -36,8 +48,11 @@ build() {
 package() {
   install -Dm644 "$srcdir/initcpio-install-overlayroot" "$pkgdir/usr/lib/initcpio/install/overlayroot"
   install -Dm644 "$srcdir/initcpio-hooks-overlayroot" "$pkgdir/usr/lib/initcpio/hooks/overlayroot"
-  install -Dm644 "$srcdir/journald-volatile-storage.conf" "$pkgdir/etc/systemd/journald.conf.d/volatile-storage.conf"
+#  install -Dm644 "$srcdir/journald-volatile-storage.conf" "$pkgdir/etc/systemd/journald.conf.d/volatile-storage.conf"
   install -Dm755 "$srcdir/rwrootfs" "$pkgdir/usr/bin/rwrootfs"
   install -Dm755 "$srcdir/fsck.overlay" "$pkgdir/usr/bin/fsck.overlay"
+  install -Dm644 "$srcdir/mkinitcpio-overlayroot.conf" "$pkgdir/etc/mkinitcpio-overlayroot.conf"
+  install -Dm644 "$srcdir/mkinitcpio-overlayroot.preset" "$pkgdir/etc/mkinitcpio.d/overlayroot.preset"
   install -Dm644 "$srcdir/overlayroot-motd.sh" "$pkgdir/etc/profile.d/overlayroot-motd.sh"
+  install -Dm644 "$srcdir/90-overlayroot.hook" "$pkgdir/usr/share/libalpm/hooks/90-overlayroot.hook"
 }

README.md

@@ -32,34 +32,46 @@ Install this package
 makepkg -si
 ```
 
-Then try rebooting, it should boot as normal.
+After installation, a new `initramfs-overlayroot.img` initramfs will be automatically created but not used.
+Try rebooting, it should boot as normal.
 
 ### Enable overlayroot hook
 
-Then add `overlayroot` to your `HOOKS` array in `/etc/mkinitcpio.conf` and rebuild the initramfs by running
+To enable overlayroot hook, you need to change the `initramfs` command in `/boot/config.txt`:
 
 ```
-mkinitcpio -P
+initramfs initramfs-overlayroot.img followkernel
 ```
 
-and reboot. It should boot as normal.
+Try rebooting, it should boot as normal because there is no `overlayroot` on the commandline yet.
 
-### Enable overlayroot in commandline
+### Enable overlayroot backed on RAM (tmpfs)
 
-With the initramfs in place, you can now enable overlayroot by adding `overlayroot` to the end of `/boot/cmdline.txt`
+To boot with overlayroot over tmpfs, just add `overlayroot=tmpfs` to the end of `/boot/cmdline.txt`.
 
 ```
-root=/dev/mmcblk0p2 rw rootwait console=ttyAMA0,115200 console=tty1 selinux=0 plymouth.enable=0 smsc95xx.turbo_mode=N dwc_otg.lpm_enable=0 kgdboc=ttyAMA0,115200 elevator=noop overlayroot
+root=/dev/mmcblk0p2 rw rootwait console=ttyAMA0,115200 console=tty1 selinux=0 plymouth.enable=0 smsc95xx.turbo_mode=N dwc_otg.lpm_enable=0 kgdboc=ttyAMA0,115200 elevator=noop overlayroot=tmpfs
 ```
 
 and reboot. You should see a warning during login that any changes you make to your filesystem will be non-persistent after this point.
 
+### Enable overlayroot backed on USB
+
+To boot with overlayroot backed on USB, just add `overlayroot=<device>` to the end of `/boot/cmdline.txt`. You can specify the device to use by device name or tag, e.g. `/dev/sda2`, `LABEL=ROOT_USB`, `UUID=xxx`, refer to mount(8) manpage for details.
+
+```
+root=/dev/mmcblk0p2 rw rootwait console=ttyAMA0,115200 console=tty1 selinux=0 plymouth.enable=0 smsc95xx.turbo_mode=N dwc_otg.lpm_enable=0 kgdboc=ttyAMA0,115200 elevator=noop overlayroot=LABEL=ROOT_USB
+```
+
+and reboot. You will not see a warning during login because any changes you make to your filesystem will be stored on the USB device.
+
+
 ### Set filesystems readonly
 
 You can now also set the entire root filesystem as readonly by changing `rw` to `ro` in `/boot/cmdline.txt`
 
 ```
-root=/dev/mmcblk0p2 ro rootwait console=ttyAMA0,115200 console=tty1 selinux=0 plymouth.enable=0 smsc95xx.turbo_mode=N dwc_otg.lpm_enable=0 kgdboc=ttyAMA0,115200 elevator=noop overlayroot
+root=/dev/mmcblk0p2 ro rootwait console=ttyAMA0,115200 console=tty1 selinux=0 plymouth.enable=0 smsc95xx.turbo_mode=N dwc_otg.lpm_enable=0 kgdboc=ttyAMA0,115200 elevator=noop overlayroot=tmpfs
 ```
 
 and adding `ro` to `/etc/fstab`
@@ -74,18 +86,22 @@ and adding `ro` to `/etc/fstab`
 
 ## Editing the root filesystem
 
-You can run `rwrootfs` to remount all file systems as read-write and change into an interactive shell in your SD card file system. After exiting that shell, the fileystems will remain read-write until next reboot.
+You can run `rwrootfs` to remount all file systems as read-write and change into an interactive shell in your SD card file system. After exiting that shell, the filesystems will remain read-write until next reboot.
 
 Alternatively you can undo all changes from [Enable overlayroot in commandline](#enable-overlayroot-in-commandline) and [Set filesystems readonly](#set-filesystems-readonly) and reboot. This is the recommended way of system upgrades.
 
+## Resyncing the SDCARD
+
+When using USB backend, you can resync automatically the SDCARD by creating a file named `/overlayroot.resync`. Upon reboot, files (virtually) removed from the SDCARD will be removed from the SDCARD for real and the content of the USB backend will be moved to the SDCARD.
+
 ## Debugging
 
 Sometimes, overlayroot may cause trouble during boot time. To boot without it simply remove `overlayroot` from `/boot/cmdline.txt`.
 
 If you still have problems, you can also try removing the initramfs by removing
 
 ```
-initramfs initramfs-linux.img followkernel
+initramfs initramfs-overlayroot.img followkernel
 ```
 
 from `/boot/config.txt`.

initcpio-hooks-overlayroot

@@ -2,9 +2,13 @@
 
 run_hook() {
   if [ "${overlayroot}" ]; then
-    # Create overlay tree in RAM
     mkdir -p /overlay
-    mount -t tmpfs overlayroot /overlay
+    if [ "${overlayroot}" = "tmpfs" ]; then
+      mount -t tmpfs overlayroot /overlay
+    else
+      mount ${overlayroot} /overlay
+      [ $? -eq 0 ] || mount -t tmpfs overlayroot /overlay
+    fi
     mkdir -p /overlay/upper
     mkdir -p /overlay/work
     mkdir -p /overlay/lower
@@ -22,6 +26,45 @@ run_latehook() {
     rm /new_root
     mkdir -p /new_root
 
+    if [ -e "/overlay/upper/overlayroot.resync" ]; then
+
+      echo "overlayroot: Resyncing lower and upper ..."
+
+      awk '$2 == "/overlay/lower" && $4 ~ /ro,/ { exit 1 }' /proc/mounts
+      is_ro=$?
+
+      if [ $is_ro -eq 1 ]; then
+        mount -o rw,remount /overlay/lower
+      fi
+
+      # Delete all files which have been whited out from upper
+      echo "overlayroot: Deleting all files from lower that have been wiped from upper ..."
+      (cd /overlay/upper && find . -type c -print) | while read path; do
+        [ "$(stat -c '%t %T' /overlay/upper/$path)" = "0 0" ] || continue
+	rm -fr /overlay/lower/$path /overlay/upper/$path
+      done
+
+      # Delete all files from lower that exist in upper
+      echo "overlayroot: Deleting all files from lower that exist in upper ..."
+      (cd /overlay/upper && find . ! -type d -print0) | (cd /overlay/lower && xargs -0 rm -fr)
+
+      # Copy upper to lower
+      echo "overlayroot: Copying all files from upper to lower ..."
+      (cd /overlay/upper && tar cf - .) | (cd /overlay/lower && tar xf -)
+
+      # Delete overlayroot.resync from lower
+      rm /overlay/lower/overlayroot.resync
+
+      # Delete all files from upper
+      echo "overlayroot: Deleting all files from upper ..."
+      rm -fr /overlay/upper/* /overlay/upper/.*
+
+      # Remount 'ro' after we are finished
+      if [ $is_ro -eq 1 ]; then
+        mount -o ro,remount /overlay/lower
+      fi
+    fi
+
     # Build overlay FS and mount it to /new_root
     mount -t overlay overlay -o lowerdir=/overlay/lower,upperdir=/overlay/upper,workdir=/overlay/work /new_root
 

mkinitcpio-overlayroot.conf

@@ -0,0 +1,4 @@
+. /etc/mkinitcpio.conf
+
+BINARIES+=( find mount rm tar xargs )
+HOOKS+=( overlayroot )

mkinitcpio-overlayroot.preset

@@ -0,0 +1,4 @@
+. /etc/mkinitcpio.d/linux-raspberrypi.preset
+
+default_config="/etc/mkinitcpio-overlayroot.conf"
+default_image="/boot/initramfs-overlayroot.img"

overlayroot-motd.sh

@@ -1,10 +1,10 @@
-if grep -qs 'overlayroot' /proc/cmdline; then
+if [ "$(awk '$2 == "/overlay" { print $3 }' /proc/mounts)" = "tmpfs" ]; then
 cat << EOF
 
-==> WARNING: Overlayroot in effect.
-None of the changes you make will be preseved after reboot.
+==> WARNING: overlayroot backed on tmpfs in effect.  None of the changes you
+make will be preserved after reboot.
 
-To disable overlayroot remove the 'overlayroot' argument
-from the kernel commandline.
+To disable overlayroot remove the 'overlayroot' argument from the kernel
+commandline.
 EOF
 fi