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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Eelco Chaudron <echaudro@redhat.com>
Cc: Y Song <ys114321@gmail.com>, Yonghong Song <yhs@fb.com>,
	Xdp <xdp-newbies@vger.kernel.org>, bpf <bpf@vger.kernel.org>
Subject: Re: Trying the bpf trace a bpf xdp program
Date: Sat, 7 Dec 2019 08:51:19 -0800
Message-ID: <CAADnVQ+DHuDS2xZbjsEfBYX5t761dbCih6p-=NaCNU9OJEMk8A@mail.gmail.com> (raw)
In-Reply-To: <78D7857B-82E4-42BC-85E1-E3D7C97BF840@redhat.com>

On Fri, Dec 6, 2019 at 5:05 AM Eelco Chaudron <echaudro@redhat.com> wrote:
>
> Thanks the hint that it should be the jitted arguments solved it… And
> you quick example worked, just in case some one else is playing with it,
> here is my working example:
>
> // SPDX-License-Identifier: GPL-2.0
> #include <linux/bpf.h>
> #include "bpf_helpers.h"
> #include "bpf_trace_helpers.h"
>
> #define bpf_debug(fmt, ...)                \
> {                                          \
>      char __fmt[] = fmt;                    \
>      bpf_trace_printk(__fmt, sizeof(__fmt), \
>                       ##__VA_ARGS__);       \
> }
>
> struct net_device {
>      /* Structure does not need to contain all entries,
>       * as "preserve_access_index" will use BTF to fix this... */
>      int                    ifindex;
> } __attribute__((preserve_access_index));
>
> struct xdp_rxq_info {
>      /* Structure does not need to contain all entries,
>       * as "preserve_access_index" will use BTF to fix this... */
>      struct net_device *dev;
>      __u32 queue_index;
> } __attribute__((preserve_access_index));
>
> struct xdp_buff {
>      void *data;
>      void *data_end;
>      void *data_meta;
>      void *data_hard_start;
>      unsigned long handle;
>      struct xdp_rxq_info *rxq;
> } __attribute__((preserve_access_index));
>
>
> BPF_TRACE_1("fentry/xdp_prog_simple", trace_on_entry,
>              struct xdp_buff *, xdp)
> {
>      bpf_debug("fentry: [ifindex = %u, queue =  %u]\n",
>                xdp->rxq->dev->ifindex, xdp->rxq->queue_index);
>      return 0;
> }
>
>
> BPF_TRACE_2("fexit/xdp_prog_simple", trace_on_exit,
>              struct xdp_buff*, xdp, int, ret)
> {
>      bpf_debug("fexit: [ifindex = %u, queue =  %u, ret = %d]\n",
>                xdp->rxq->dev->ifindex, xdp->rxq->queue_index, ret);

This is great. Could you submit it as selftests/bpf ?
It will help others trying to do the same.
May be instead of bpf_debug() use global variables so the test will be
self checking ?

Long term we should teach verifier to understand 'struct xdp_md*'
in addition to 'struct xdp_buff *'. That will help ease of use.

  reply index

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <E53E0693-1C3A-4B47-B205-DC8E5DAF3619@redhat.com>
2019-11-28 18:18 ` Alexei Starovoitov
2019-11-28 19:16   ` Eelco Chaudron
2019-11-28 19:47     ` Alexei Starovoitov
2019-11-29 16:30       ` Eelco Chaudron
2019-11-29 16:52         ` Yonghong Song
2019-12-02 16:34           ` Eelco Chaudron
2019-12-02 16:48             ` Yonghong Song
2019-12-04 13:19               ` Eelco Chaudron
2019-12-04 14:58                 ` Yonghong Song
2019-12-04 18:01                   ` Yonghong Song
2019-12-04 18:52                     ` Eelco Chaudron
2019-12-05 12:40                       ` Eelco Chaudron
2019-12-05 17:35                         ` Y Song
2019-12-06 13:04                           ` Eelco Chaudron
2019-12-07 16:51                             ` Alexei Starovoitov [this message]
2019-12-19 11:06                               ` Eelco Chaudron
2019-12-04 16:31                 ` Andrii Nakryiko
2019-12-04 18:03                   ` John Fastabend
2019-12-04 21:19                     ` Andrii Nakryiko

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