feat: Add method Run to BPFProg

[geyslan]

feat: Add method Run to BPFProg

Run method is used to load and run the BPF program without attaching it
to any hook. This is useful for testing the BPF program.

It makes use of the bpf(BPF_PROG_TEST_RUN) via bpf_prog_test_run_opts().

The prog-run selftest is added to test the Run method. More examples
can be found in the linux kernel source code:
tools/testing/selftests/bpf/prog_tests.

Original code #428 was authored by sc07kvm, and this commiter have only
made cosmetics adjustments.

[NDStrahilevitz]

LGTM, a nice addition indeed.

[NDStrahilevitz]

I think it would be nice to add an error here when the program type isn't compatible (rather than relying on an internal failure).

[geyslan]

It will be dependent on kernel version support, e.g.:

• https://elixir.bootlin.com/linux/v6.9.3/source/net/bpf/test_run.c#L728 (supported)
• https://elixir.bootlin.com/linux/v6.9.3/source/include/linux/bpf.h#L3075 (unsupported)
• https://elixir.bootlin.com/linux/v6.9.3/source/include/linux/bpf.h#L2817 (unsupported)

The output for ENOTSUPP is failed to run program: errno 524. https://elixir.bootlin.com/linux/v6.9.3/source/include/linux/errno.h#L27

.Error() doesn't find a correct entry, since "not supported" for syscall is ENOTSUP 95. https://github.com/golang/sys/blob/master/unix/zerrors_linux_amd64.go#L614

[geyslan]

WDYT? If you agree, we must check all others returns for this ENOTSUPP.

failed to run program: operation not supported

diff --git a/prog.go b/prog.go
index e47c8ec..56ea57e 100644
--- a/prog.go
+++ b/prog.go
@@ -779,7 +779,11 @@ func (p *BPFProg) Run(opts *RunOpts) error {
 
        retC := C.bpf_prog_test_run_opts(C.int(p.FileDescriptor()), optsC)
        if retC < 0 {
-               return fmt.Errorf("failed to run program: %w", syscall.Errno(-retC))
+               errno := syscall.Errno(-retC)
+               if errno == 524 { // ENOTSUPP https://elixir.bootlin.com/linux/v6.9.3/source/include/linux/errno.h#L27
+                       errno = syscall.ENOTSUP
+               }
+               return fmt.Errorf("failed to run program: %s", errno)
        }
 
        // update runOpts with the values from the kernel and libbpf

[geyslan]

Anyway, merging. If decided for it, we can tackle it in a bunch.