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SubjectRe: Testing the thermal genetlink API
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Hi Nicolas,

thanks for using the netlink and giving those feedbacks even you are
unhappy with them.

On 28/02/2022 12:03, Nicolas Cavallari wrote:
> I've played a bit with the thermal netlink interface and it wasn't pleasant:
>
> 1. The way attributes are used is painful. Instead of using arrays of
> nested structs-like, it flattens them into a big nested attr where
> you have to guess when an entry starts and when it ends.
> libnl provides no helper for this case:
>
> [{nla_type=TZ|F_NESTED},
> [{nla_type=TZ_ID}, 1]
> [{nla_type=TZ_NAME}, "name1"]
> [{nla_type=TZ_ID}, 2]
> [{nla_type=TZ_NAME}, "name2"]
> [{nla_type=TZ_ID}, 3]
> [{nla_type=TZ_NAME}, "name3"]
> [{nla_type=TZ_ID}, 4]
> [{nla_type=TZ_NAME}, "name4"]
> ]
>
> 2. The genl_cmd types are not unique between multicast events and
> command replies. If you send genl_cmd=3 (CMD_TZ_GET_TEMP) and you
> get a genl_cmd=3 reply, you cannot know if it is a CMD_TZ_GET_TEMP
> response or a EVENT_TZ_DISABLE because both have genl_cmd=3, but
> completely different semantics.
> 3. The API is heavy. Getting the complete information about all thermal
> zones requires 1 + 6 * thermal_zones netlink requests, each of them
> only returning few information. You need most of them to merely
> translate the event's TZ_ID/TZ_TRIP_ID/CDEV_ID to names.

That is part of the discovery and it should happen only once when you
get the thermal information.

> 4. THERMAL_GENL_CMD_TZ_GET_TRIP cause an oops if the thermal zone driver
> does not have a get_trip_hyst callback.
> This concerns all drivers, short of two. A patch follows.

Great, thanks for the fix.

> For the record, I couldn't find any open source program using this API.
> It's also not enabled in all distributions.

The netlink support is very recent. A library has been posted [1] and
hopefully it can helps you to get rid of all the complexity.

Thanks for testing

-- D.

[1]
https://lore.kernel.org/all/20220218125334.995447-1-daniel.lezcano@linaro.org/


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