Not part of C or POSIX, but since there is no procfs right now, I thought it would be nice to have an interface to query process information.
It works like this: you pass the process ID and a pointer to a struct pstat (can be null).
If the process ID is -1, the kernel picks the process with the highest PID.
Then, if the pointer to a pstat struct is not null, the kernel fills it in with the process's information, and returns the process's PID.