linux-kernel - Re: [PATCH net-next 02/11] tools: ynl-gen: generate nested array policies

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Message-ID: <6e31a9e0-5450-4b45-a557-2aa08d23c25a@fiberby.net>
Date: Sat, 6 Sep 2025 14:13:01 +0000
From: Asbjørn Sloth Tønnesen <ast@...erby.net>
To: Jacob Keller <jacob.e.keller@...el.com>,
 "Jason A. Donenfeld" <Jason@...c4.com>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: Donald Hunter <donald.hunter@...il.com>, Simon Horman <horms@...nel.org>,
 Andrew Lunn <andrew+netdev@...n.ch>, wireguard@...ts.zx2c4.com,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 Johannes Berg <johannes.berg@...el.com>
Subject: Re: [PATCH net-next 02/11] tools: ynl-gen: generate nested array
 policies

CC: Johannes

On 9/6/25 12:19 AM, Jacob Keller wrote:
> On 9/4/2025 3:01 PM, Asbjørn Sloth Tønnesen wrote:
>> This patch adds support for NLA_POLICY_NESTED_ARRAY() policies.
>>
>> Example spec (from future wireguard.yaml):
>> -
>>    name: wgpeer
>>    attributes:
>>      -
>>        name: allowedips
>>        type: indexed-array
>>        sub-type: nest
>>        nested-attributes: wgallowedip
>>
>> yields NLA_POLICY_NESTED_ARRAY(wireguard_wgallowedip_nl_policy).
>>
>> This doesn't change any currently generated code, as it isn't
>> used in any specs currently used for generating code.
>>
>> Signed-off-by: Asbjørn Sloth Tønnesen <ast@...erby.net>
>> ---
> 
> Is this keyed of off the sub-type? Does you mean that all the existing
> uses of 'sub-type: nest' don't generate code today? Or that this
> _attr_policy implementation is not called yet?

Thanks for the reviews. Yeah, it is a careful wording, because we have
specs matching it, but there aren't any source files that triggers
ynl-gen to generate code based on those specs.

Therefore this patch, doesn't result in any code changes when running:
$ ./tools/net/ynl/ynl-regen.sh -f

Actually ynl-gen generates a fictive "{ .type = NLA_INDEXED_ARRAY, }"
policy, without this patch, leading to a build failure.

> I checked and we have quite a number of uses:
> 
>> $ rg 'sub-type: nest'
>> Documentation/netlink/specs/nlctrl.yaml
 >> [..]
>> Documentation/netlink/specs/tc.yaml
>> [..]
>> Documentation/netlink/specs/rt-link.yaml
>> [..]
>> Documentation/netlink/specs/nl80211.yaml
>> [..]

None of those currently have a generated netlink policy.

These are the netlink policies currently generated by ynl-gen:
$ git grep -h -B1 'YNL-GEN kernel source' | grep '^/\*[^ ]'
/*      Documentation/netlink/specs/dpll.yaml */
/*      Documentation/netlink/specs/ovpn.yaml */
/*      Documentation/netlink/specs/team.yaml */
/*      Documentation/netlink/specs/lockd.yaml */
/*      Documentation/netlink/specs/nfsd.yaml */
/*      Documentation/netlink/specs/netdev.yaml */
/*      Documentation/netlink/specs/devlink.yaml */
/*      Documentation/netlink/specs/handshake.yaml */
/*      Documentation/netlink/specs/fou.yaml */
/*      Documentation/netlink/specs/mptcp_pm.yaml */
/*      Documentation/netlink/specs/net_shaper.yaml */

Johannes introduced NLA_NESTED_ARRAY and the NLA_POLICY_NESTED_ARRAY()
macro in commit 1501d13596b9 for use in nl80211, and it's therefore
used in net/wireless/nl80211.c, but outside of that the macro is
only sparsely adopted (only by mac80211_hwsim.c and nf_tables_api.c).

Wireguard adopts the macro in this RFC patch:
https://lore.kernel.org/netdev/20250904220255.1006675-2-ast@fiberby.net/