base-files: sysupgrade: always setup overlay when creating backup

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.

Cc: Luiz Angelo Daros de Luca <luizluca@gmail.com>
Cc: Christian Marangi <ansuelsmth@gmail.com>
Cc: Jo-Philipp Wich <jo@mein.io>
Cc: Jonas Gorski <jonas.gorski@gmail.com>
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>

diff --git a/package/base-files/files/sbin/sysupgrade b/package/base-files/files/sbin/sysupgrade
index 43e129e1d77ca00bc0eea41903c788db2eab9643..66bdf95de01735c16256ce0ff71ac49140e5bb84 100755 (executable)
--- a/package/base-files/files/sbin/sysupgrade
+++ b/package/base-files/files/sbin/sysupgrade
@@ -24,7 +24,6 @@ export NEED_IMAGE=
 export HELP=0
 export FORCE=0
 export TEST=0
-export UMOUNT_ETCBACKUP_DIR=0
 
 # parse options
 while [ -n "$1" ]; do
@@ -224,6 +223,8 @@ include /lib/upgrade
 
 do_save_conffiles() {
        local conf_tar="$1"
+       local tmp
+       local dir
 
        [ "$(rootfs_type)" = "tmpfs" ] && {
                echo "Cannot save config while running from ramdisk." >&2
@@ -234,17 +235,21 @@ do_save_conffiles() {
        run_hooks "$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.
+       tmp="$(mktemp -d -t overlay.XXXXXX)"
+       mkdir -p "$tmp/upper" "$tmp/work" "$tmp/backup"
+       dir="$tmp/backup"
+       if ! mount -t overlay overlay -o lowerdir=/,upperdir="$tmp/upper",workdir="$tmp/work" "$dir"; then
+               echo "Cannot mount backup overlay to $dir." >&2
+               ask_bool 0 "Abort" && exit
+               dir=""
+       fi
+
        if [ "$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
@@ -252,23 +257,22 @@ do_save_conffiles() {
                        \( -exec test -f /rom/{} \; -exec echo {} rom \; \) -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..."
        [ "$VERBOSE" -gt 1 ] && TAR_V="v" || TAR_V=""
        sed -i -e 's,^/,,' "$CONFFILES"
-       tar c${TAR_V}zf "$conf_tar" -C / -T "$CONFFILES"
+       tar c${TAR_V}zf "$conf_tar" -C "${dir:-/}" -T "$CONFFILES"
        local err=$?
        if [ "$err" -ne 0 ]; then
                echo "Failed to create the configuration backup."
                rm -f "$conf_tar"
        fi
 
-       [ "$UMOUNT_ETCBACKUP_DIR" -eq 1 ] && {
-               umount "$ETCBACKUP_DIR"
-               rm -rf "$RAMFS"
-       }
+       umount "$dir"
+       rm -rf "$tmp"
+
        rm -f "$CONFFILES"
 
        return "$err"