By overflow, I suspect you mean it grew beyond the maximum size the file system allows? Or did you pregrow the file to a
 size and used pwrite to write at certain offsets? What file system is it? fs-qnx4.so or fs-qnx6.so, or even something 
else? 

Generally, the behaviour of QNX filesystems in such a case is not documented. I have requested that the mechanisms that 
the QNX filesystems use to reach their corresponding maximum level of reliability to be documented in detail - maybe it 
will happen for 6.4.2.

For your problem I suggest the straight forward approach:
- reduce length of log messages
- reduce number of log messages
- write a thread that monitors the length of the log file once a day (?) and if too long, lock access to it with a mutex
 or so and archive it (e.g. rename, move, create new empty one).


- Malte