netdev - Re: [PATCH net] devlink: Fix devlink_param_driverinit_value

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Date:   Wed, 5 Sep 2018 08:26:15 -0600
From:   David Ahern <dsahern@...il.com>
To:     Moshe Shemesh <moshe@...lanox.com>,
        "David S. Miller" <davem@...emloft.net>
Cc:     Jiri Pirko <jiri@...lanox.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] devlink: Fix devlink_param_driverinit_value_set()
 stub return code

On 9/5/18 6:48 AM, Moshe Shemesh wrote:
> 
> 
> On 9/4/2018 7:13 PM, David Ahern wrote:
>> On 9/4/18 7:04 AM, Moshe Shemesh wrote:
>>> The stub function returned -EOPNOTSUPP while CONFIG_NET_DEVLINK is off.
>>> It caused false warning during driver load. Driver needs to update
>>> devlink on a parameter value if devlink module is there, if not it
>>> doesn't need any error code.
>>>
>>> Fixes: ec01aeb1803e ("devlink: Add support for get/set driverinit
>>> value")
>>> Signed-off-by: Moshe Shemesh <moshe@...lanox.com>
>>> Acked-by: Jiri Pirko <jiri@...lanox.com>
>>> ---
>>>   include/net/devlink.h | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/include/net/devlink.h b/include/net/devlink.h
>>> index b9b89d6..b467357 100644
>>> --- a/include/net/devlink.h
>>> +++ b/include/net/devlink.h
>>> @@ -781,7 +781,7 @@ static inline bool
>>> devlink_dpipe_table_counter_enabled(struct devlink *devlink,
>>>   devlink_param_driverinit_value_set(struct devlink *devlink, u32
>>> param_id,
>>>                      union devlink_param_value init_val)
>>>   {
>>> -    return -EOPNOTSUPP;
>>> +    return 0;
>>>   }
>>>     static inline void
>>>
>>
>> This should be handled by the driver -- check for -EOPNOTSUPP and not
>> log an error.
> 
> This is a stub inline function.
> The return value would be ambiguous as the non-stub function can also
> return -EOPNOTSUPP, in case the driver-init mode is not supported for a
> parameter.
>>
>> devlink is generic infrastructure. If a call is made and the operation
>> is not supported, then devlink should return an error.
> 
> In general the stub functions should take care that the driver won't
> feel the missing code as much as possible. That's why
> devlink_params_register() returns success and so should this function.
>>

A driver is accessing core infrastructure to set a value; core infra can
not because the code is not compiled in. The driver should be told that
the option is not enabled, and it is at the moment with the -EOPNOTSUPP
return code.

That is similar to devlink_dpipe_table_resource_set which returns
-EOPNOTSUPP when devlink is compiled out.