[xdp-hints] Re: [PATCH bpf V7 1/7] selftests/bpf: xdp_hw_metadata default disable bpf_printk

[Stanislav Fomichev <sdf@google.com>]

On Sat, Apr 8, 2023 at 12:24 PM Jesper Dangaard Brouer
<brouer@redhat.com> wrote:
>
> The tool xdp_hw_metadata can be used by driver developers
> implementing XDP-hints kfuncs.  The tool transfers the
> XDP-hints via metadata information to an AF_XDP userspace
> process. When everything works the bpf_printk calls are
> unncesssary.  Thus, disable bpf_printk by default, but
> make it easy to reenable for driver developers to use
> when debugging their driver implementation.
>
> This also converts bpf_printk "forwarding UDP:9091 to AF_XDP"
> into a code comment.  The bpf_printk's that are important
> to the driver developers is when bpf_xdp_adjust_meta fails.
> The likely mistake from driver developers is expected to
> be that they didn't implement XDP metadata adjust support.
>
> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
> ---
>  .../testing/selftests/bpf/progs/xdp_hw_metadata.c  |   16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c b/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
> index 4c55b4d79d3d..980eb60d8e5b 100644
> --- a/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
> +++ b/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
> @@ -5,6 +5,19 @@
>  #include <bpf/bpf_helpers.h>
>  #include <bpf/bpf_endian.h>
>
> +/* Per default below bpf_printk() calls are disabled.  Can be
> + * reenabled manually for convenience by XDP-hints driver developer,
> + * when troublshooting the drivers kfuncs implementation details.
> + *
> + * Remember BPF-prog bpf_printk info output can be access via:
> + *  /sys/kernel/debug/tracing/trace_pipe
> + */
> +//#define DEBUG        1
> +#ifndef DEBUG
> +#undef  bpf_printk
> +#define bpf_printk(fmt, ...) ({})
> +#endif

Are you planning to eventually do somethike similar to what I've
mentioned in [0]? If not, should I try to send a patch?

0: https://lore.kernel.org/netdev/CAKH8qBupRYEg+SPMTMb4h532GESG7P1QdaFJ-+zrbARVN9xrdA@mail.gmail.com/

> +
>  struct {
>         __uint(type, BPF_MAP_TYPE_XSKMAP);
>         __uint(max_entries, 256);
> @@ -49,11 +62,10 @@ int rx(struct xdp_md *ctx)
>         if (!udp)
>                 return XDP_PASS;
>
> +       /* Forwarding UDP:9091 to AF_XDP */
>         if (udp->dest != bpf_htons(9091))
>                 return XDP_PASS;
>
> -       bpf_printk("forwarding UDP:9091 to AF_XDP");
> -
>         ret = bpf_xdp_adjust_meta(ctx, -(int)sizeof(struct xdp_meta));
>         if (ret != 0) {
>                 bpf_printk("bpf_xdp_adjust_meta returned %d", ret);
>
>