scripts/qemu-guest-agent/fsfreeze-hook

#!/bin/sh

# This script is executed when the guest agent receives fsfreeze-freeze and
# fsfreeze-thaw commands, provided that the --fsfreeze-hook (-F) option of
# qemu-ga is specified and the script is placed in /etc/qemu/fsfreeze-hook or in
# the path specified together with -F. When the agent receives fsfreeze-freeze
# requests, this script is called with "freeze" as its argument before the
# filesystem is frozen. And for fsfreeze-thaw requests, it is called with "thaw"
# as its argument after the filesystem is thawed.

LOGFILE=/var/log/qga-fsfreeze-hook.log
FSFREEZE_D=$(dirname -- "$0")/fsfreeze-hook.d

# Check whether file $1 is a backup or rpm-generated file and should be ignored
is_ignored_file() {
    case "$1" in
        *~ | *.bak | *.orig | *.rpmnew | *.rpmorig | *.rpmsave | *.sample | *.dpkg-old | *.dpkg-new | *.dpkg-tmp | *.dpkg-dist | *.dpkg-bak | *.dpkg-backup | *.dpkg-remove)
            return 0 ;;
    esac
    return 1
}

USE_SYSLOG=0
# if log file exists but is not writable, fallback to syslog
[ -e "$LOGFILE" ] && [ ! -w "$LOGFILE" ] && USE_SYSLOG=1
# try to update log file and fallback to syslog if it fails
touch "$LOGFILE" >/dev/null 2>&1 || USE_SYSLOG=1

# Ensure the log file is writable, fallback to syslog if not
log_message() {
    if [ "$USE_SYSLOG" -eq 0 ]; then
        printf "%s: %s\n" "$(date)" "$1" >>"$LOGFILE"
    else
        logger -t qemu-ga-freeze-hook "$1"
    fi
}

# Iterate executables in directory "fsfreeze-hook.d" with the specified args
[ ! -d "$FSFREEZE_D" ] && exit 0

for file in "$FSFREEZE_D"/* ; do
    is_ignored_file "$file" && continue
    [ -x "$file" ] || continue

    log_message "Executing $file $*"
    if [ "$USE_SYSLOG" -eq 0 ]; then
        "$file" "$@" >>"$LOGFILE" 2>&1
        STATUS=$?
    else
        # We want to pipe the output of $file through 'logger' and also
        # capture its exit status. Since we are a POSIX script we can't
        # use PIPESTATUS, so instead this is a trick borrowed from
        # https://unix.stackexchange.com/questions/14270/get-exit-status-of-process-thats-piped-to-another/70675#70675
        # which uses command-groups and redirection to get the exit status.
        # This is equivalent to
        #   "$file" "$@" 2>&1 | logger -t qemu-ga-freeze-hook
        # plus setting the exit status of the pipe to the exit
        # status of the first command rather than the last one.
        { { { {
                "$file" "$@" 2>&1 3>&- 4>&-
                echo $? >&3
            } | logger -t qemu-ga-freeze-hook >&4
            } 3>&1
          } | { read -r xs ; exit "$xs"; }
        } 4>&1
        STATUS=$?
    fi

    if [ "$STATUS" -ne 0 ]; then
        log_message "Error: $file finished with status=$STATUS"
    else
        log_message "$file finished successfully"
    fi
done

exit 0