To complete previous anwswer from meuh, if you would like env file to be dynamic, you could define a setup function.
create env/local-dev.env,env/integ.env file with some content
define a method to load this
$(eval ENV_FILE := env/$(1).env)
@echo " - setup env $(ENV_FILE)"
$(eval include env/$(1).env)
If you look at net/ipv4/Makefile, you’ll see that tcp_ipv4.o is part of obj-y, which means it can only be built as part of the kernel, it can’t be built as a module.
If you want your changes to be taken into account, you’ll have to rebuild the complete kernel. Since you’re short of disk space, you can build only the kernel, install that, then clean the build ...
This specific error isn’t particularly important, it’s a “trick” used to break the build if a given value is determined to be zero. To understand why the build is failing, you need to look at the next error message, which should include
note: in expansion of macro ‘BUILD_BUG_ON_ZERO’
followed by the expression which caused the error.
In your case, the ...