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

From: Krzesimir Nowak <krzesimir@kinvolk.io>
To: bpf@vger.kernel.org
Cc: "Alban Crequy" <alban@kinvolk.io>,
	"Iago López Galeiras" <iago@kinvolk.io>,
	"Krzesimir Nowak" <krzesimir@kinvolk.io>,
	"Quentin Monnet" <quentin.monnet@netronome.com>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Martin KaFai Lau" <kafai@fb.com>,
	"Song Liu" <songliubraving@fb.com>, "Yonghong Song" <yhs@fb.com>,
	"Jakub Kicinski" <jakub.kicinski@netronome.com>,
	"Stanislav Fomichev" <sdf@google.com>,
	"Prashant Bhole" <bhole_prashant_q7@lab.ntt.co.jp>,
	"Okash Khawaja" <osk@fb.com>,
	"David Calavera" <david.calavera@gmail.com>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [BPF v1] tools: bpftool: Fix JSON output when lookup fails
Date: Wed,  5 Jun 2019 21:17:06 +0200	[thread overview]
Message-ID: <20190605191707.24429-1-krzesimir@kinvolk.io> (raw)

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@netronome.com>
Signed-off-by: Krzesimir Nowak <krzesimir@kinvolk.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

