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

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Message-ID: <2b9fc661-e061-4699-861b-39af8bf84359@icloud.com>
Date: Tue, 20 Aug 2024 21:40:23 +0800
From: Zijun Hu <zijun_hu@...oud.com>
To: Ira Weiny <ira.weiny@...el.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>, Davidlohr Bueso
 <dave@...olabs.net>, Jonathan Cameron <jonathan.cameron@...wei.com>,
 Dave Jiang <dave.jiang@...el.com>,
 Alison Schofield <alison.schofield@...el.com>,
 Vishal Verma <vishal.l.verma@...el.com>,
 Dan Williams <dan.j.williams@...el.com>,
 Takashi Sakamoto <o-takashi@...amocchi.jp>, Timur Tabi <timur@...nel.org>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-cxl@...r.kernel.org,
 linux1394-devel@...ts.sourceforge.net, netdev@...r.kernel.org,
 Zijun Hu <quic_zijuhu@...cinc.com>
Subject: Re: [PATCH v2 1/4] driver core: Make parameter check consistent for
 API cluster device_(for_each|find)_child()

On 2024/8/20 20:53, Ira Weiny wrote:
> Zijun Hu wrote:
>> From: Zijun Hu <quic_zijuhu@...cinc.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);
}

>> Fixed by using consistent check (!parent || !parent->p) for the cluster.
>>
>> Signed-off-by: Zijun Hu <quic_zijuhu@...cinc.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.

> Ira
> 
>>  		return NULL;
>>  
>>  	klist_iter_init(&parent->p->klist_children, &i);
>>
>> -- 
>> 2.34.1
>>
> 
>