linux-kernel - Re: [BPF v1] tools: bpftool: Fix JSON output when lookup fails

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Message-ID: <CAEf4BzYUg+FbBfCe-DTLrrT07ifK49NRFhLWye+Ej1JiFYwioQ@mail.gmail.com>
Date:   Wed, 5 Jun 2019 12:36:54 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Krzesimir Nowak <krzesimir@...volk.io>
Cc:     bpf <bpf@...r.kernel.org>, Alban Crequy <alban@...volk.io>,
        Iago López Galeiras <iago@...volk.io>,
        Quentin Monnet <quentin.monnet@...ronome.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Prashant Bhole <bhole_prashant_q7@....ntt.co.jp>,
        Okash Khawaja <osk@...com>,
        David Calavera <david.calavera@...il.com>,
        Networking <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [BPF v1] tools: bpftool: Fix JSON output when lookup fails

On Wed, Jun 5, 2019 at 12:18 PM Krzesimir Nowak <krzesimir@...volk.io> wrote:
>
> In commit 9a5ab8bf1d6d ("tools: bpftool: turn err() and info() macros
> into functions") one case of error reporting was special cased, so it
> could report a lookup error for a specific key when dumping the map
> element. What the code forgot to do is to wrap the key and value keys
> into a JSON object, so an example output of pretty JSON dump of a
> sockhash map (which does not support looking up its values) is:
>
> [
>     "key": ["0x0a","0x41","0x00","0x02","0x1f","0x78","0x00","0x00"
>     ],
>     "value": {
>         "error": "Operation not supported"
>     },
>     "key": ["0x0a","0x41","0x00","0x02","0x1f","0x78","0x00","0x01"
>     ],
>     "value": {
>         "error": "Operation not supported"
>     }
> ]
>
> Note the key-value pairs inside the toplevel array. They should be
> wrapped inside a JSON object, otherwise it is an invalid JSON. This
> commit fixes this, so the output now is:
>
> [{
>         "key": ["0x0a","0x41","0x00","0x02","0x1f","0x78","0x00","0x00"
>         ],
>         "value": {
>             "error": "Operation not supported"
>         }
>     },{
>         "key": ["0x0a","0x41","0x00","0x02","0x1f","0x78","0x00","0x01"
>         ],
>         "value": {
>             "error": "Operation not supported"
>         }
>     }
> ]
>
> Fixes: 9a5ab8bf1d6d ("tools: bpftool: turn err() and info() macros into functions")
> Cc: Quentin Monnet <quentin.monnet@...ronome.com>
> Signed-off-by: Krzesimir Nowak <krzesimir@...volk.io>
> ---

Acked-by: Andrii Nakryiko <andriin@...com>

>  tools/bpf/bpftool/map.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
> index 3ec82904ccec..5da5a7311f13 100644
> --- a/tools/bpf/bpftool/map.c
> +++ b/tools/bpf/bpftool/map.c
> @@ -716,12 +716,14 @@ static int dump_map_elem(int fd, void *key, void *value,
>                 return 0;
>
>         if (json_output) {
> +               jsonw_start_object(json_wtr);
>                 jsonw_name(json_wtr, "key");
>                 print_hex_data_json(key, map_info->key_size);
>                 jsonw_name(json_wtr, "value");
>                 jsonw_start_object(json_wtr);
>                 jsonw_string_field(json_wtr, "error", strerror(lookup_errno));
>                 jsonw_end_object(json_wtr);
> +               jsonw_end_object(json_wtr);
>         } else {
>                 const char *msg = NULL;
>
> --
> 2.20.1
>