EMMC cannot display all device nodes under / dev /
Please try to create the node with the command like this:
# mknod /dev/mmcblk1p8 b 9 40
Here 9 and 40 are not actual numbers.
Please first do "ls -l /dev/mmcblk1p7" to get its major and minor numbers,
then use major and minor+1 for mmcblk1p8.