First of all, thanks Martin for pointing it out.

We've made busybox default to two binaries, busybox.nosuid and busybox.suid.
We also add a variable 'BUSYBOX_SPLIT_SUID‘ to control its behavior.
Now that we can have a busybox version with only one binary (/bin/busybox) or we can have a version with two binaries (/bin/busybox.nosuid and /bin/busybox.suid), the on-device upgrade issue starts to become a problem.

We have to support four upgrade paths:
A: busybox[split]
B: busybox[no split]

A --(upgrade)--> B
B --(upgrade)--> A
A --(upgrade)--> A
B --(upgrade)--> B

This problem can be more complex if we take into consideration the upgrade issue of other related packages, for example, busybox-syslog.

The goal here is to make any upgrade path above successful.

//Chen Qi