[PATCH RFC] base-files: sysupgrade: always setup overlay when creating backup

[Luiz Angelo Daros de Luca]

> From: Rafał Miłecki <rafal at milecki.pl>
>
> Setting overlay while creating backup allows including extra files in
> archive without actually writing them to flash. Right now this feature
> is limited to /etc/backup/ directory and is used only for including
> installed_packages.txt.
>
> Extend this solution to make it more generic:
> 1. Always mount overlay while creating backup
> 2. Overlay whole / to don't limit it to /etc/backup/
>
> This allows including any additional files in backups and adding more
> sysupgrade features.

It is a nice feature. Thanks.

>
> Cc: Luiz Angelo Daros de Luca <luizluca at gmail.com>
> Cc: Christian Marangi <ansuelsmth at gmail.com>
> Cc: Jo-Philipp Wich <jo at mein.io>
> Cc: Jonas Gorski <jonas.gorski at gmail.com>
> Signed-off-by: Rafał Miłecki <rafal at milecki.pl>
> ---
> This will allow me to include /etc/uci-defaults/ scripts in backups so
> we can e.g. have script disabling previously disabled services.
>
>  package/base-files/files/sbin/sysupgrade | 37 ++++++++++++++----------
>  1 file changed, 21 insertions(+), 16 deletions(-)
>
> diff --git a/package/base-files/files/sbin/sysupgrade b/package/base-files/files/sbin/sysupgrade
> index 1fcd44da2a..1e09f65e07 100755
> --- a/package/base-files/files/sbin/sysupgrade
> +++ b/package/base-files/files/sbin/sysupgrade
> @@ -237,7 +237,8 @@ include /lib/upgrade
>  create_backup_archive() {
>         local conf_tar="$1"
>
> -       local umount_etcbackup_dir=0
> +       local overlay
> +       local dir
>
>         [ "$(rootfs_type)" = "tmpfs" ] && {
>                 echo "Cannot save config while running from ramdisk." >&2
> @@ -248,17 +249,20 @@ create_backup_archive() {
>         run_hooks "$CONFFILES" $sysupgrade_init_conffiles
>         ask_bool 0 "Edit config file list" && vi "$CONFFILES"
>
> +       # Mount root directory with temporary overlay on top of it.
> +       # This allows including extra (temporary) files in backup archive
> +       # without messing actual rootfs.
> +       overlay="$(mktemp -d -t overlay.XXXXXX)"
> +       mkdir -p "$overlay/upper" "$overlay/work"
> +       dir="$(mktemp -d -t backup.XXXXXX)"

You could avoid two mktemp creating a single unique parent directory.
It makes the cleanup simpler.

> +       if ! mount -t overlay overlay -o lowerdir=/,upperdir="$overlay/upper",workdir="$overlay/work" "$dir"; then
> +               echo "Cannot mount backup overlay to $dir." >&2
> +               ask_bool 0 "Abort" && exit
> +       fi
> +
>         if [ "$SAVE_INSTALLED_PKGS" -eq 1 ]; then
>                 echo "${INSTALLED_PACKAGES}" >> "$CONFFILES"
> -               mkdir -p "$ETCBACKUP_DIR"
> -               # Avoid touching filesystem on each backup
> -               RAMFS="$(mktemp -d -t sysupgrade.XXXXXX)"
> -               mkdir -p "$RAMFS/upper" "$RAMFS/work"
> -               mount -t overlay overlay -o lowerdir=$ETCBACKUP_DIR,upperdir=$RAMFS/upper,workdir=$RAMFS/work $ETCBACKUP_DIR &&
> -                       umount_etcbackup_dir=1 || {
> -                               echo "Cannot mount '$ETCBACKUP_DIR' as tmpfs to avoid touching disk while saving the list of installed packages." >&2
> -                               ask_bool 0 "Abort" && exit
> -                       }
> +               mkdir -p "$dir/$ETCBACKUP_DIR"
>
>                 # Format: pkg-name<TAB>{rom,overlay,unkown}
>                 # rom is used for pkgs in /rom, even if updated later
> @@ -266,22 +270,23 @@ create_backup_archive() {
>                         \( -exec test -f /rom/{} \; -exec echo {} rom \; \) -o \
>                         \( -exec test -f /overlay/upper/{} \; -exec echo {} overlay \; \) -o \
>                         \( -exec echo {} unknown \; \) \
> -                       \) | sed -e 's,.*/,,;s/\.control /\t/' > ${INSTALLED_PACKAGES}
> +                       \) | sed -e 's,.*/,,;s/\.control /\t/' > "$dir/${INSTALLED_PACKAGES}"
>         fi
>
>         v "Saving config files..."
> +       sed -i 's/^\///' "$CONFFILES" # Drop leading slashes
>         [ "$VERBOSE" -gt 1 ] && TAR_V="v" || TAR_V=""
> -       tar c${TAR_V}zf "$conf_tar" -T "$CONFFILES" 2>/dev/null
> +       tar c${TAR_V}zf "$conf_tar" -C "${dir:-/}" -T "$CONFFILES"

These were already part of an PR that fixed a couple of sysupgrade issues:
https://github.com/openwrt/openwrt/pull/11022 (since Oct 2022 but
still relevant), including here.

>         if [ "$?" -ne 0 ]; then
>                 echo "Failed to create the configuration backup."
>                 rm -f "$conf_tar"
>                 exit 1

Like this one. You need to unmount and delete everything before
bailing out. Check the PR.
Maybe we should merge it and rebase your change over it. Or you can
merge it into this patch.

>         fi
>
> -       [ "$umount_etcbackup_dir" -eq 1 ] && {
> -               umount "$ETCBACKUP_DIR"
> -               rm -rf "$RAMFS"
> -       }
> +       umount "$dir"
> +       rm -rf "$dir"
> +       rm -rf "$overlay"
> +
>         rm -f "$CONFFILES"
>  }
>
> --
> 2.35.3
>