2) if you are correct, then isn't it a violation of copyright law to use a socket or a pipe to talk to a GPL program? For example, if I execute popen("parallel ..."), I'm using a pipe to talk to a GPLed program (assuming "parallel" is GNU parallel). I expect this program to adhere to a specific command line interface. My program won't work with anything else. Is my program violating the GPL by running GNU parallel as a subprocess? Most people would say "no". This position seems incoherent to me.
One of two conditions must then hold: either a) dlopen has legal significance, or b) much of the Linux ecosystem is out of compliance with the GPL because it attempts to use pipe() to circumvent the GPL and this approach doesn't actually work. Which is it?
1) it's not clear your interpretation of what makes software "derivative" is correct. One interesting analysis is https://studylib.net/doc/18120956/triggering-infection--dist......
2) if you are correct, then isn't it a violation of copyright law to use a socket or a pipe to talk to a GPL program? For example, if I execute popen("parallel ..."), I'm using a pipe to talk to a GPLed program (assuming "parallel" is GNU parallel). I expect this program to adhere to a specific command line interface. My program won't work with anything else. Is my program violating the GPL by running GNU parallel as a subprocess? Most people would say "no". This position seems incoherent to me.
One of two conditions must then hold: either a) dlopen has legal significance, or b) much of the Linux ecosystem is out of compliance with the GPL because it attempts to use pipe() to circumvent the GPL and this approach doesn't actually work. Which is it?