On 11/6/25 12:00 PM, Corentin ARNOULD via discuss wrote:
> Hello,
Hi.
>
>
> I figured the JSON output format is not exactly how I expected it to be.
> Most of the data is represented using arrays, with headers being a
> dictionary of all the column names, looking like a CSV with JSON format.
> I provided an output for a newly created bridge for reference bellow.
>
> I looked a bit into the code, and it seems like there is an internal
> representation of the data in json, and passing "-f json" just print the
> internal representation. Which is not really readable by humans (or
> "jq")...
It should be a valid JSON. So, while it's not that easy to read, tools
like jq should be able to work with it. Though, yes, it's not really
straightforward.
> I wrote a patch that modify the json format for output, but I
> was wondering it was a good idea to change the json format directly or
> if it was better to use an alternative name (like json2 or something),
> as it would break backward compatibility if users used this feature in
> scripts.
>
> When working on that, I found something interesting in the way arrays
> are represented. Depending on the size, an array with the cardinality of
> 1 would not be displayed as a set, but with 0 or 2 elements it would be
> represented as a set:
>
> With 0 element: ["set", []]
>
> With 1 element: 0
>
> With 2 elements: ["set", [0, 1]]
>
> I tried patching this too, but it breaks a lot of tests (because it
> changes the output format) and I was thinking that maybe this is an
> intended feature.
>
>
> So here are two questions:
>
> - Is a patch regarding json readability welcome ? If yes, should the
> "json" format be modified or a new one being created ?
>
> - Is it expected to have a different representation of array with
> cardinality 1 ?
The JSON output format today is tied to the internal representation of
the data inside the database. Everything in a database is a set and
it represents 1-element sets as single values to avoid extra clutter
for columns with scalar types. Empty sets can't be represented this way,
so they are reported as empty sets. So, this is expected.
I think, changing the format as it appears on a wire or in the database
file is not an option for compatibility reasons, but we can make control
utilities like ovs-vsctl print out the data prettier, if there is a desire
for that. A separate format option might be a better choice for it, again,
for compatibility reasons. We may call it 'json-compact' or something
like this. We may also omit empty sets and arrays from the output to
reduce the visual clutter even further.
Best regards, Ilya Maximets.
>
>
> I would love to help, but just trying to make it right.
>
> Have a good day,
>
> Regards,
>
> ---
>
> Current representation: "ovs-vsctl -f json list bridge | jq"
>
> {
> "data": [
> [
> [
> "uuid",
> "59e32bd7-19b9-4532-b6dd-3b0ab50d2823"
> ],
> [
> "set",
> []
> ],
> [
> "set",
> []
> ],
> [
> "set",
> [
> "0000d62be3593245"
> ]
> ],
> "",
> "<built-in>",
> [
> "map",
> []
> ],
> [
> "set",
> []
> ],
> [
> "set",
> []
> ],
> [
> "map",
> []
> ],
> [
> "set",
> []
> ],
> false,
> [
> "set",
> []
> ],
> "br0",
> [
> "set",
> []
> ],
> [
> "map",
> []
> ],
> [
> "set",
> [
> [
> "uuid",
> "4d6002d5-9451-4b19-95a7-34ac5b07b1e8"
> ]
> ]
> ],
> [
> "set",
> []
> ],
> false,
> [
> "map",
> []
> ],
> [
> "set",
> []
> ],
> [
> "map",
> []
> ],
> false
> ]
> ],
> "headings": [
> "_uuid",
> "auto_attach",
> "controller",
> "datapath_id",
> "datapath_type",
> "datapath_version",
> "external_ids",
> "fail_mode",
> "flood_vlans",
> "flow_tables",
> "ipfix",
> "mcast_snooping_enable",
> "mirrors",
> "name",
> "netflow",
> "other_config",
> "ports",
> "protocols",
> "rstp_enable",
> "rstp_status",
> "sflow",
> "status",
> "stp_enable"
> ]
> }
>
> ---
>
> Proposed JSON representation: "ovs-vsctl -f json list bridge | jq"
>
> {
> "data": [
> {
> "_uuid": "7b0b6a72-7f53-4789-94d3-5046adc554b2",
> "auto_attach": [],
> "controller": [],
> "datapath_id": "0000726a0b7b8947",
> "datapath_type": "",
> "datapath_version": "<built-in>",
> "external_ids": {},
> "fail_mode": [],
> "flood_vlans": [],
> "flow_tables": {},
> "ipfix": [],
> "mcast_snooping_enable": false,
> "mirrors": [],
> "name": "br0",
> "netflow": [],
> "other_config": {},
> "ports": "655fb0d8-926a-43ea-9fa1-9106f7be7e8d",
> "protocols": [],
> "rstp_enable": false,
> "rstp_status": {},
> "sflow": [],
> "status": {},
> "stp_enable": false
> }
> ]
> }
>
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