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?
I would argue that yes, you're not working around the GPL by going through a pipe. Your program still doesn't work if the remote process gets killed, so it's dependent on it.
> 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.
> 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?
Afaik the FSF agrees with your dichotomy and expresses the latter opinion. Take for instance their faq "You cannot incorporate GPL-covered software in a proprietary system. ... However, in many cases you can distribute the GPL-covered software alongside your proprietary system. To do this validly, you must make sure that the free and nonfree programs communicate at arms length, that they are not combined in a way that would make them effectively a single program. The difference between this and “incorporating” the GPL-covered software is partly a matter of substance and partly form. The substantive part is this: if the two programs are combined so that they become effectively two parts of one program, then you can't treat them as two separate programs. So the GPL has to cover the whole thing."
In another question, they address the notion of what might be considered a single combined porogram. "It depends on how the main program invokes its plug-ins. If the main program uses fork and exec to invoke plug-ins, and they establish intimate communication by sharing complex data structures, or shipping complex data structures back and forth, that can make them one single combined program. A main program that uses simple fork and exec to invoke plug-ins and does not establish intimate communication between them results in the plug-ins being a separate program.
"If the main program dynamically links plug-ins, and they make function calls to each other and share data structures, we believe they form a single combined program, which must be treated as an extension of both the main program and the plug-ins. If the main program dynamically links plug-ins, but the communication between them is limited to invoking the ‘main’ function of the plug-in with some options and waiting for it to return, that is a borderline case.
"Using shared memory to communicate with complex data structures is pretty much equivalent to dynamic linking."
So I don't think that the FSF intends that you can use a technical means to escape linking. You cannot take a GPL library and write a pair of libraries which expose its functions via a socket because the result would almost certainly involve "function calls to each other and share[d] data structures".
As to whether this puts into jeopardy anyone in particular who uses Linux or libmysql in proprietary systems without additional licences, well, that is a different matter. The FSF's interpretation of the GPL tells you something about when the FSF might sue you and about what revisions might be made to the GPL in the future. But it doesn't tell you about when the copyright holders of Linux or libmysql might sue you, or what they will do if there's a GPL v5.2 released tomorrow.
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?