[yocto] The problem of do_rootfs_append

[Neil.Wu at Emerson.com]

Hi, all
I'm building specific rootfs image. Add the do_rootfs_append() task  in core-image-specific.bb,
core-image-specific.bb:

SUMMARY = "creaet the customer rootfs"
require ${TOPDIR}/../meta/recipes-core/images/core-image-minimal.bb
IMAGE_INSTALL = "readline-dev linux-libc-headers-dev json-glib busybox-udhcpc "
do_rootfs_append() {
        cp -rf ${IMAGE_ROOTFS}/data/etc/ ${IMAGE_ROOTFS}/etc/
        rm -rf ${IMAGE_ROOTFS}/data/etc/
}

It always meet the error as follows:
ERROR: ExpansionError during parsing /home/ectrs/poky/meta-emerson-ecosys/recipes-core/images/core-image-ecosys.bb: Failure expanding variable do_rootfs: IndentationError: unexpected indent (<string>, line 14)

I'm pleasant receive your reply. If you know how to solve it , please help me .
Thank you very much.

Neil