nixos/filesystems: succeed mount-pstore.service without backend

              set -eu

              # if the pstore module is builtin it will have mounted the persistent store automatically. it may also be already mounted for other reasons.

              ${pkgs.util-linux}/bin/mountpoint -q /sys/fs/pstore || ${pkgs.util-linux}/bin/mount -t pstore -o nosuid,noexec,nodev pstore /sys/fs/pstore

              # wait up to five seconds (arbitrary, happened within one in testing) for the backend to be registered and the files to appear. a systemd path unit cannot detect this happening; and succeeding after a restart would not start dependent units.

              TRIES=50

              # wait up to 1.5 seconds for the backend to be registered and the files to appear. a systemd path unit cannot detect this happening; and succeeding after a restart would not start dependent units.

              TRIES=15

              while [ "$(cat /sys/module/pstore/parameters/backend)" = "(null)" ]; do

                if (( $TRIES )); then

                  sleep 0.1

                  TRIES=$((TRIES-1))

                else

                  echo "Persistent Storage backend was not registered in time." >&2

                  exit 1

                  break

                fi

              done

            '';