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

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Message-Id: <20190605191707.24429-1-krzesimir@kinvolk.io>
Date:   Wed,  5 Jun 2019 21:17:06 +0200
From:   Krzesimir Nowak <krzesimir@...volk.io>
To:     bpf@...r.kernel.org
Cc:     Alban Crequy <alban@...volk.io>,
        Iago López Galeiras <iago@...volk.io>,
        Krzesimir Nowak <krzesimir@...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>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [BPF v1] tools: bpftool: Fix JSON output when lookup fails

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>
---
 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