On Sat, 02 Mar 2019 14:36:12 -0500, Jeffrey Walton said: > I feel like I am missing something... Does Linux consider the modem a > shared resource instead of an exclusive resource? What use cases > support two different programs sending commands to the modem at the > same time? The Linux kernel has exactly zero clue what a "modem" is. It's talking to a serial port, and doesn't care where the other end of the serial cable is. If you have a onboard modem, that cable may be all of 2 mm long and consist of a bunch of traces between two chips on a PCB, or even internal connections between two sides of a chip, but it's still there. So the correct question is "what use cases have two programs talking to the same serial port"? And the answer is: A lot. For a long time, there were these things called "terminals", that the younger folk may not have encountered. And a very common use case was to login via a terminal. At that point, you usually had a login shell like bash or similar running and often doing I/O to the terminal - and if you ran any sub-processes, they also would do I/O to the terminal. So consider the following bash one-liner: % for i in `seq 1 10`; do echo "Loop number $i"; date; sleep 1; done How and why does this work? (Hint 1: 'echo' is a bash builtin, Hint 2: think about how a shell handles stdin/out for child processes) _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
