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Filename : rtc-sys-time-init
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#!/bin/sh

# Adjust system time for the following reasons:
#     1) Sync system time to RTC time
#         - On older kernel versions, RTC modules with HCTOSYS enabled cannot sync system time with
#           RTC time (attribute hctosys==0)
#     2) Correct driver/module system time sync to invalid time (earlier than most recent time stamp)
#         - Built-in/loadable RTC driver with HCTOSYS enabled may set invalid time due to .e.g
#           uninitialized RTC or bad battery
#
# If the RTC time is not valid, or cannot be set, forward the system time to most recent timestamp

set -eu

journal() {
    pri=$1
    shift
    lvl=
    case "$pri" in
        "error")
            lvl="<3>"
            ;;
        "warning")
            lvl="<4>"
            ;;
        "debug")
            lvl="<7>"
            ;;
        *)
            lvl="<6>"
            ;;
    esac

    # Apply priority level to all lines
    printf "%s\n" "$@" | while IFS= read -r line; do
        printf "%s\n" "$lvl$line"
    done
}

# Expects single argument RTC device node /dev/rtc* (instance name dev-rtc* with escaping undone)
dev_node=$1

# ... or a path in /sys
if ! [ -c "${dev_node}" ]; then
    dev_node="$(udevadm info --query=property --path "${dev_node}" | sed "/^DEVNAME=/{;s///;q};d")"
fi

# Get systemd timestamp file created during core build
clock_epoch_stamp=0
if [ -e "/usr/lib/clock-epoch" ]; then
    clock_epoch_stamp=$(stat -L "/usr/lib/clock-epoch" -c '%Y')
else
    journal warning "Warning: cannot stat /usr/lib/clock-epoch"
fi
clock_epoch_date=$(date -d @"$clock_epoch_stamp")
journal debug "core/systemd build timetamp: $clock_epoch_date"

# Get systemd-timesyncd timestamp file initialized to systemd build time and updated periodically
# (default 60s) and at shutdown
timesync_clock_stamp=0
if [ -e "/var/lib/systemd/timesync/clock" ]; then
    timesync_clock_stamp="$(stat -L "/var/lib/systemd/timesync/clock" -c '%Y')"
else
    journal warning "Warning: cannot stat /var/lib/systemd/timesync/clock (expected on first boot only)"
fi
timesync_clock_date=$(date -d @"$timesync_clock_stamp")
journal debug "timesyncd timestamp: $timesync_clock_date"

most_recent_stamp=$((clock_epoch_stamp > timesync_clock_stamp ? clock_epoch_stamp : timesync_clock_stamp))

sys_time_set_res=1
if udevadm info --attribute-walk --name="$dev_node" | grep -q 'ATTR{hctosys}=="1"'; then
    sys_time_set_res=0
    echo "Kernel synced system time to RTC $dev_node time"
else
    echo "Reading RTC $dev_node time..."
    if ! rtc_stamp=$(hwclock -r -u -f "$dev_node" 2>/dev/null); then
        journal error "Error: cannot read RTC $dev_node"
    else
        rtc_stamp=$(date -d "$rtc_stamp" +%s)
        rtc_date=$(date -d @"$rtc_stamp")
        echo "Successfully read RTC time: $rtc_date"

        if [ "$rtc_stamp" -gt "$most_recent_stamp" ]; then
            echo "RTC time is valid, syncing system time..."
            if hwclock -s --noadjfile -u -f "$dev_node" 2>/dev/null; then
                echo "Successfully synced system time"
                exit 0
            else
                journal error "Error: cannot sync system time"
            fi
        else
            journal error "Error: RTC time invalid, skipping system time sync"
        fi
    fi
fi

# At this point either (1) the RTC module synced the system time or (2) this script failed
# to sync system time. In both cases we need to ensure that system time is not behind the
# most recent timestamp.
now_stamp=$(date +'%s')
if [ "$now_stamp" -lt "$most_recent_stamp" ]; then
    echo "Moving system time forward to most recent timestamp..."
    if date -s @"$most_recent_stamp" >/dev/null 2>&1; then
        echo "Successfully moved system time forward"
    else
        journal error "Error: cannot forward system time"
        exit 1
    fi
else
    echo "System time is ahead of most recent timestamp, skipping fixup"
fi

exit $sys_time_set_res