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Message-ID: <e30eac3b-4244-460d-ab0b-baaa659999fe@icloud.com>
Date: Wed, 21 Aug 2024 22:44:27 +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 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@...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);
>> }
>
> Ok. Thanks.
>
>>
>>>> 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.
>
> 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
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