tools: bpftool: Fix JSON output when lookup fails

[ Upstream commit 1884c066579a7a274dd981a4d9639ca63db66a23 ]

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>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
index 994a7e0d16fb..14f581b562bd 100644
--- a/tools/bpf/bpftool/map.c
+++ b/tools/bpf/bpftool/map.c
@@ -713,12 +713,14 @@ 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 {
 		if (errno == ENOENT)
 			print_entry_plain(map_info, key, NULL);