Wrote a USB automatically mount rules, the following
The KERNEL=="sd [a-z] *," ACTION=="add", SUBSYSTEM=="block", and the SYMLINK +="USB", RUN +="./bin/sh/root/load_device sh % k "

When normal insert USB device,/dev/USB address partitions are equipment, such as sda1, sda2, so this is normal, but when I plug in mobile hard disk/dev/USB points to the device, namely sda, SDB, so that you can't use/dev/USB mount, this is probably what reason is caused?

I already tested, trigger a rule order is equipment, equipment partition will then trigger a, such as the sda trigger a, sda1 will then trigger a, so is not caused by order,