I wanted to change the way modbus master polls the slaves, but as I see, it is implemented in seroutils...
Now if all slaves are online, they are queried one after the other. If a slave goes offline, it is queried "retries" times in one round, then it is qualified offline.
My version would always query each slave only one time in a round, and qualify a slave offline only if "retries" number of rounds has elapsed without a proper answer.
It's not a big difference, but gives more time for the network to recover from a transient failure.
I don't know, if this algorithm was suitable for other modbus users/uses, or could be implemented only as an option.