How to safely use new Linux functions?

Question

I'm writing code that uses sched_setaffinity, which requires kernel 2.5.8 or later. I've been trying to find out if these things are possible:

1. Systems with older kernels to compile this gracefully, perhaps just ignoring that code segment entirely.
2. If I send someone with an older kernel a compiled binary, it will step over this function or simply print a warning.

I guess my question is, how do you use new kernel functions safely, without breaking the entire application when using an older system?

Answer 1

Use dlopen() with NULL as the filename, and dlsym() the function you want to use. If the dlsym() succeeds, call the function through the function pointer that was returned.

Answer 2

Are you trying to get your program to link or to run? You can invoke the system call directly via the glibc syscall() function without needing a recent C library. Obviously it's going to fail on earlier systems without support (a quick test shows the kernel returns -1 == ENOSYS for unimplemented syscall numbers), so you will need to test for that.