netdev - Re: [PATCH net-next v4 3/6] devlink: support default values for param-get and param-set

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Message-ID: <a56cc76f-7278-49d5-a9ca-5d04d61cb8f8@gmail.com>
Date: Tue, 18 Nov 2025 09:05:20 -0500
From: Daniel Zahka <daniel.zahka@...il.com>
To: "Loktionov, Aleksandr" <aleksandr.loktionov@...el.com>,
 Jiri Pirko <jiri@...nulli.us>, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
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 Brett Creeley <brett.creeley@....com>, Andrew Lunn <andrew+netdev@...n.ch>,
 Michael Chan <michael.chan@...adcom.com>,
 Pavan Chebbi <pavan.chebbi@...adcom.com>,
 "Nguyen, Anthony L" <anthony.l.nguyen@...el.com>,
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Cc: "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
 "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
 "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>
Subject: Re: [PATCH net-next v4 3/6] devlink: support default values for
 param-get and param-set

On 11/18/25 2:27 AM, Loktionov, Aleksandr wrote:
>> diff --git a/include/uapi/linux/devlink.h
>> b/include/uapi/linux/devlink.h index 157f11d3fb72..e7d6b6d13470 100644
>> --- a/include/uapi/linux/devlink.h
>> +++ b/include/uapi/linux/devlink.h
>> @@ -639,6 +639,9 @@ enum devlink_attr {
>>
>>   	DEVLINK_ATTR_HEALTH_REPORTER_BURST_PERIOD,	/* u64 */
>>
>> +	DEVLINK_ATTR_PARAM_VALUE_DEFAULT,	/* dynamic */
>> +	DEVLINK_ATTR_PARAM_RESET_DEFAULT,	/* flag */
>> +
> The patch introduces a new UAPI attribute DEVLINK_ATTR_PARAM_VALUE_DEFAULT but Documentation/netlink/specs/devlink.yaml only documents param-reset-default.
> The spec should also describe the output attribute that appears in the nested param-value dump ("default" value), otherwise the generated tooling/specs are out of sync with UAPI and the committed generated C (netlink_gen.c).
>
> I'm afraid you forgot to add a YAML entry for the nested attribute (e.g. under the param-value attribute set, typically alongside param-value-data and param-value-cmode), describing its type per param and the bool/u8 encoding rule covered in the commit message.
> Am I right?

Hello. Thank you for the review.

As I understand it, devlink.yaml omits entries of enum devlink_attr that 
are annotated as "dynamic". This is what creates two of the holes in the 
devlink attribute set in devlink.yaml where the "TODO: fill in the 
attributes in between" comments appear. Dynamic types are basically 
tagged unions, where the tag is held by a different attribute: 
DEVLINK_ATTR_PARAM_TYPE. The netlink yaml schema doesn't have a good way 
to encode this. That is why param-value-data, and now 
param-value-default cannot be in devlink.yaml. The best that could be 
done for now would probably be to add them with 'type: binary'.