Subject: RE: [PATCH v4 bpf-next 05/10] selftests: xsk: query for native XDP support

From: John Fastabend <[email-masked]>
Date: Fri, 17 Jun 2022 19:12:00 -0700

Maciej Fijalkowski wrote:
> Currently, xdpxceiver assumes that underlying device supports XDP in
> native mode - it is fine by now since tests can run only on a veth pair.
> Future commit is going to allow running test suite against physical
> devices, so let us query the device if it is capable of running XDP
> programs in native mode. This way xdpxceiver will not try to run
> TEST_MODE_DRV if device being tested is not supporting it.
> 
> Acked-by: Magnus Karlsson <[email-masked]>
> Signed-off-by: Maciej Fijalkowski <[email-masked]>
> ---
>  tools/testing/selftests/bpf/xdpxceiver.c | 36 ++++++++++++++++++++++--
>  1 file changed, 34 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/xdpxceiver.c b/tools/testing/selftests/bpf/xdpxceiver.c
> index e5992a6b5e09..a1e410f6a5d8 100644
> --- a/tools/testing/selftests/bpf/xdpxceiver.c
> +++ b/tools/testing/selftests/bpf/xdpxceiver.c
> @@ -98,6 +98,8 @@
>  #include <unistd.h>
>  #include <stdatomic.h>
>  #include <bpf/xsk.h>
> +#include <bpf/bpf.h>
> +#include <linux/filter.h>
>  #include "xdpxceiver.h"
>  #include "../kselftest.h"
>  
> @@ -1605,10 +1607,37 @@ static void ifobject_delete(struct ifobject *ifobj)
>  	free(ifobj);
>  }
>  
> +static bool is_xdp_supported(struct ifobject *ifobject)
> +{
> +	int flags = XDP_FLAGS_DRV_MODE;
> +
> +	LIBBPF_OPTS(bpf_link_create_opts, opts, .flags = flags);
> +	struct bpf_insn insns[2] = {
> +		BPF_MOV64_IMM(BPF_REG_0, XDP_PASS),
> +		BPF_EXIT_INSN()
> +	};
> +	int ifindex = if_nametoindex(ifobject->ifname);
> +	int prog_fd, insn_cnt = ARRAY_SIZE(insns);
> +	int err;
> +
> +	prog_fd = bpf_prog_load(BPF_PROG_TYPE_XDP, NULL, "GPL", insns, insn_cnt, NULL);
> +	if (prog_fd < 0)
> +		return false;
> +
> +	err = bpf_xdp_attach(ifindex, prog_fd, flags, NULL);
> +	if (err)

Best not to leave around prog_fd in the error case or in the
good case.

> +		return false;
> +
> +	bpf_xdp_detach(ifindex, flags, NULL);
> +

close(prog_fd)

> +	return true;
> +}
> +