linux-kernel - Re: [PATCH 2/5] driver core: Introduce an API constify_device_find_child

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Message-ID: <2024081311-mortality-opal-cf0f@gregkh>
Date: Tue, 13 Aug 2024 12:57:43 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: quic_zijuhu <quic_zijuhu@...cinc.com>
Cc: Zijun Hu <zijun_hu@...oud.com>, "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>,
	Ira Weiny <ira.weiny@...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>,
	linux-kernel@...r.kernel.org, linux-cxl@...r.kernel.org,
	linux1394-devel@...ts.sourceforge.net, netdev@...r.kernel.org
Subject: Re: [PATCH 2/5] driver core: Introduce an API
 constify_device_find_child_helper()

On Tue, Aug 13, 2024 at 06:50:04PM +0800, quic_zijuhu wrote:
> On 8/13/2024 5:45 PM, Greg Kroah-Hartman wrote:
> > On Sun, Aug 11, 2024 at 08:18:08AM +0800, Zijun Hu wrote:
> >> From: Zijun Hu <quic_zijuhu@...cinc.com>
> >>
> >> Introduce constify_device_find_child_helper() to replace existing
> >> device_find_child()'s usages whose match functions will modify
> >> caller's match data.
> > 
> > Ick, that's not a good name, it should be "noun_verb" with the subsystem being on the prefix always.
> > 
> okay, got it.
> 
> is it okay to use device_find_child_mut() suggested by Przemek Kitszel ?

No, just switch all callers over to be const and keep the same name.

> > But why is this even needed?  Device pointers are NOT const for the
> > obvious reason that they can be changed by loads of different things.
> > Trying to force them to be const is going to be hard, if not impossible.
> > 
> 
> [PATCH 3/5] have more discussion about these questions with below link:
> https://lore.kernel.org/all/8b8ce122-f16b-4207-b03b-f74b15756ae7@icloud.com/
> 
> 
> The ultimate goal is to make device_find_child() have below prototype:
> 
> struct device *device_find_child(struct device *dev, const void *data,
> 		int (*match)(struct device *dev, const void *data));
> 
> Why ?
> 
> (1) It does not make sense, also does not need to, for such device
> finding operation to modify caller's match data which is mainly
> used for comparison.
> 
> (2) It will make the API's match function parameter have the same
> signature as all other APIs (bus|class|driver)_find_device().
> 
> 
> My idea is that:
> use device_find_child() for READ only accessing caller's match data.
> 
> use below API if need to Modify caller's data as
> constify_device_find_child_helper() does.
> int device_for_each_child(struct device *dev, void *data,
>                     int (*fn)(struct device *dev, void *data));
> 
> So the The ultimate goal is to protect caller's *match data* @*data  NOT
> device @*dev.

Ok, sorry, I was confused.

thanks,

greg k-h