My boss at work needs to be making a monitoring app for a program they are using. Because of their business needs, I can NOT use any sort of virtual serial port. The data goes in and out of /dev/ttyUSB0, and the application MUST be connected to /dev/ttyUSB0. I have already discussed a design that utilizes virtual serial ports created by socat so I can get what goes in and out the serial port, without interrupting the transfer of data. But that design was rejected. And he suggested that I make it through something called Port Mirroring or Reading the information without using up the resource like apparently Putty can do in Windows. I am a huge lost at what to do, or how to approach this. 
How do I read from a Serial Port, without using up its resource?
monitoring;serial port