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: <66c4a4e15302b_2f02452943@iweiny-mobl.notmuch>
Date: Tue, 20 Aug 2024 09:14:57 -0500
From: Ira Weiny <ira.weiny@...el.com>
To: Zijun Hu <zijun_hu@...oud.com>, 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()

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.

Ira