Re: [PATCH v2 1/4] driver core: Make parameter check consistent for API cluster device_(for_each|find)_child()

[Zijun Hu <zijun_hu@icloud.com>]

On 2024/8/20 22:14, Ira Weiny wrote:
> Zijun Hu wrote:
>> On 2024/8/20 20:53, Ira Weiny wrote:
>>> Zijun Hu wrote:
>>>> From: Zijun Hu <quic_zijuhu@quicinc.com>
>>>>
>>>> The following API cluster takes the same type parameter list, but do not
>>>> have consistent parameter check as shown below.
>>>>
>>>> device_for_each_child(struct device *parent, ...)  // check (!parent->p)
>>>> device_for_each_child_reverse(struct device *parent, ...) // same as above
>>>> device_find_child(struct device *parent, ...)      // check (!parent)
>>>>
>>>
>>> Seems reasonable.
>>>
>>> What about device_find_child_by_name()?
>>>
>>
>> Plan to simplify this API implementation by * atomic * API
>> device_find_child() as following:
>>
>> https://lore.kernel.org/all/20240811-simply_api_dfcbn-v2-1-d0398acdc366@quicinc.com
>> struct device *device_find_child_by_name(struct device *parent,
>>  					 const char *name)
>> {
>> 	return device_find_child(parent, name, device_match_name);
>> }
> 
> Ok.  Thanks.
> 
>>
>>>> Fixed by using consistent check (!parent || !parent->p) for the cluster.
>>>>
>>>> Signed-off-by: Zijun Hu <quic_zijuhu@quicinc.com>
>>>> ---
>>>>  drivers/base/core.c | 6 +++---
>>>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/drivers/base/core.c b/drivers/base/core.c
>>>> index 1688e76cb64b..b1dd8c5590dc 100644
>>>> --- a/drivers/base/core.c
>>>> +++ b/drivers/base/core.c
>>>> @@ -4004,7 +4004,7 @@ int device_for_each_child(struct device *parent, void *data,
>>>>  	struct device *child;
>>>>  	int error = 0;
>>>>  
>>>> -	if (!parent->p)
>>>> +	if (!parent || !parent->p)
>>>>  		return 0;
>>>>  
>>>>  	klist_iter_init(&parent->p->klist_children, &i);
>>>> @@ -4034,7 +4034,7 @@ int device_for_each_child_reverse(struct device *parent, void *data,
>>>>  	struct device *child;
>>>>  	int error = 0;
>>>>  
>>>> -	if (!parent->p)
>>>> +	if (!parent || !parent->p)
>>>>  		return 0;
>>>>  
>>>>  	klist_iter_init(&parent->p->klist_children, &i);
>>>> @@ -4068,7 +4068,7 @@ struct device *device_find_child(struct device *parent, void *data,
>>>>  	struct klist_iter i;
>>>>  	struct device *child;
>>>>  
>>>> -	if (!parent)
>>>> +	if (!parent || !parent->p)
>>>
>>> Perhaps this was just a typo which should have been.
>>>
>>> 	if (!parent->p)
>>> ?
>>>
>> maybe, but the following device_find_child_by_name() also use (!parent).
>>
>>> I think there is an expectation that none of these are called with a NULL
>>> parent.
>>>
>>
>> this patch aim is to make these atomic APIs have consistent checks as
>> far as possible, that will make other patches within this series more
>> acceptable.
>>
>> i combine two checks to (!parent || !parent->p) since i did not know
>> which is better.
> 
> I'm not entirely clear either.  But checking the member p makes more sense
> to me than the parent parameter.  I would expect that iterating the
> children of a device must be done only when the parent device is not NULL.
> 
> parent->p is more subtle.  I'm unclear why the API would need to allow
> that to run without error.
> 
i prefer (!parent || !parent->p) with below reasons:

1)
original API authors have such concern that either (!parent) or
(!parent->p) maybe happen since they are checked, all their concerns
can be covered by (!parent || !parent->p).

2)
It is the more robust than either (!parent) or (!parent->p)

3)
it also does not have any negative effect.

> Ira