Re: [PATCH bpf-next v2 4/5] bpf: selftests: add MPTCP test base

[Nicolas Rybowski <nicolas.rybowski@tessares.net>]

Hi Song,

Thanks for the feedback !

On Mon, Sep 14, 2020 at 8:07 PM Song Liu <song@kernel.org> wrote:
>
> On Fri, Sep 11, 2020 at 8:02 AM Nicolas Rybowski
> <nicolas.rybowski@tessares.net> wrote:
> >
> > This patch adds a base for MPTCP specific tests.
> >
> > It is currently limited to the is_mptcp field in case of plain TCP
> > connection because for the moment there is no easy way to get the subflow
> > sk from a msk in userspace. This implies that we cannot lookup the
> > sk_storage attached to the subflow sk in the sockops program.
> >
> > Acked-by: Matthieu Baerts <matthieu.baerts@tessares.net>
> > Signed-off-by: Nicolas Rybowski <nicolas.rybowski@tessares.net>
>
> Acked-by: Song Liu <songliubraving@fb.com>
>
> With some nitpicks below.
>
> > ---
> >
> > Notes:
> >     v1 -> v2:
> >     - new patch: mandatory selftests (Alexei)
> >
> [...]
> >                      int timeout_ms);
> > diff --git a/tools/testing/selftests/bpf/prog_tests/mptcp.c b/tools/testing/selftests/bpf/prog_tests/mptcp.c
> > new file mode 100644
> > index 000000000000..0e65d64868e9
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/prog_tests/mptcp.c
> > @@ -0,0 +1,119 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +#include <test_progs.h>
> > +#include "cgroup_helpers.h"
> > +#include "network_helpers.h"
> > +
> > +struct mptcp_storage {
> > +       __u32 invoked;
> > +       __u32 is_mptcp;
> > +};
> > +
> > +static int verify_sk(int map_fd, int client_fd, const char *msg, __u32 is_mptcp)
> > +{
> > +       int err = 0, cfd = client_fd;
> > +       struct mptcp_storage val;
> > +
> > +       /* Currently there is no easy way to get back the subflow sk from the MPTCP
> > +        * sk, thus we cannot access here the sk_storage associated to the subflow
> > +        * sk. Also, there is no sk_storage associated with the MPTCP sk since it
> > +        * does not trigger sockops events.
> > +        * We silently pass this situation at the moment.
> > +        */
> > +       if (is_mptcp == 1)
> > +               return 0;
> > +
> > +       if (CHECK_FAIL(bpf_map_lookup_elem(map_fd, &cfd, &val) < 0)) {
> > +               perror("Failed to read socket storage");
>
> Maybe simplify this with CHECK(), which contains a customized error message?
> Same for some other calls.
>

The whole logic here is strongly inspired from prog_tests/tcp_rtt.c
where CHECK_FAIL is used.
Also the CHECK macro will print a PASS message on successful map
lookup, which is not expected at this point of the tests.
I think it would be more interesting to leave it as it is to keep a
cohesion between TCP and MPTCP selftests. What do you think?

If there are no objections, I will send a v3 with the other requested
changes and a rebase on the latest bpf-next.

> > +               return -1;
> > +       }
> > +
> > +       if (val.invoked != 1) {
> > +               log_err("%s: unexpected invoked count %d != %d",
> > +                       msg, val.invoked, 1);
> > +               err++;
> > +       }
> > +
> > +       if (val.is_mptcp != is_mptcp) {
> > +               log_err("%s: unexpected bpf_tcp_sock.is_mptcp %d != %d",
> > +                       msg, val.is_mptcp, is_mptcp);
> > +               err++;
> > +       }
> > +
> > +       return err;
> > +}
> > +
> > +static int run_test(int cgroup_fd, int server_fd, bool is_mptcp)
> [...]
>
> > +
> > +       client_fd = is_mptcp ? connect_to_mptcp_fd(server_fd, 0) :
> > +                              connect_to_fd(server_fd, 0);
> > +       if (client_fd < 0) {
> > +               err = -1;
> > +               goto close_client_fd;
>
> This should be "goto close_bpf_object;", and we don't really need the label
> close_client_fd.
>
> > +       }
> > +
> > +       err += is_mptcp ? verify_sk(map_fd, client_fd, "MPTCP subflow socket", 1) :
>
> It doesn't really change the logic, but I guess we only need "err = xxx"?
>
> > +                         verify_sk(map_fd, client_fd, "plain TCP socket", 0);
> > +
> > +close_client_fd:
> > +       close(client_fd);
> > +
> > +close_bpf_object:
> > +       bpf_object__close(obj);
> > +       return err;
> > +}
> > +