Re: How do I implement bpf_prog_test_run with BPF CO-RE?

["Mauricio Vásquez Bernal" <mauricio@kinvolk.io>]

On Mon, Jan 17, 2022 at 2:16 AM Pony Sew <poony20115@gmail.com> wrote:
>
> Hello.
> It seems like before bpf_prog_test_run is called, you need to call
> bpf_prog_load. But in BPF CO-RE program, we already have
> <program>_bpf__open and <program>_bpf__load which basically does the
> same thing. My code look approximately like this:
>
> -----test1_load.c---------------
> #include <cgreen/cgreen.h>
>
> Ensure(Load, load_test){
>     /* should I call bpf_prog_load here? */

bpf_prog_test_run() needs prog_fd. You're already calling
bpf_firewall_bpf__load() in bpf_firewall.c, you can get the program fd
by using
prog_fd = obj->progs.<program>.prog_fd;

>     bpf_prog_test_run(/* parameters */);
>     /* what about bpf_object__close? */
> }
>
> TestSuite *load_tests() {
>     TestSuite *suite = create_test_suite();
>     return suite;
> }
>
> -----bpf_firewall.bpf.c---------
>  #include "vmlinux.h"
>  #include <bpf/bpf_helpers.h>
>
> SEC("xdp_prog")
> int xdp_prog_main(struct xdp_md *ctx){
>     /* main program */
> }
>
>  char LICENSE[] SEC("license") = "GPL";
>
> ------bpf_firewall.c---------------
> #include <cgreen/cgreen.h>
> #include <bpf/libbpf.h>
> #include <bpf/bpf.h>
> #include "bpf_firewall.skel.h"
>
> TestSuite *load_tests();
>
> int main(int argc, char **argv) {
>     struct bpf_firewall_bpf *obj;
>     int err = 0;
>
>     obj = bpf_firewall_bpf__open();
>
>     err = bpf_firewall_bpf__load(obj);
>
>     err = bpf_firewall_bpf__attach(obj);

I don't think you need to call __attach() if you only want to perform
some tests with bpf_prog_test_run.

>
>     TestSuite *suite = create_test_suite();
>     add_suite(suite, load_tests());
>     run_test_suite(suite, create_text_reporter());
>
>     bpf_firewall_bpf__destroy(obj);
>     return 0;
> }
>
> How do I implement bpf_prog_test_run with BPF CO-RE?

You don't need to worry about it. You're using the skeleton and hence
libbpf underneath, it'll take care of performing all CO-RE relocations
when loading the program.

This approach is used many times in tools/testing/selftests/bpf, for
instance tools/testing/selftests/bpf/prog_tests/map_ptr.c does exactly
what you're looking for.

>
> Best regards,
> Poony.