linux-kernel - Re: [PATCH 1/5] driver core: make struct class.dev

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Message-ID: <5b14cdea-1bbe-1900-0004-a218ba97bbcb@acm.org>
Date:   Sun, 27 Nov 2022 18:38:39 -0800
From:   Bart Van Assche <bvanassche@....org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Russ Weight <russell.h.weight@...el.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Jean Delvare <jdelvare@...e.com>,
        Johan Hovold <johan@...nel.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Leon Romanovsky <leon@...nel.org>,
        Karsten Keil <isdn@...ux-pingi.de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Keith Busch <kbusch@...nel.org>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Sebastian Reichel <sre@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Johannes Berg <johannes@...solutions.net>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Raed Salem <raeds@...dia.com>,
        Chen Zhongjin <chenzhongjin@...wei.com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Avihai Horon <avihaih@...dia.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Colin Ian King <colin.i.king@...il.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Jakob Koschel <jakobkoschel@...il.com>,
        Antoine Tenart <atenart@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Wang Yufen <wangyufen@...wei.com>, linux-block@...r.kernel.org,
        linux-media@...r.kernel.org, linux-nvme@...ts.infradead.org,
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        linux-usb@...r.kernel.org, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH 1/5] driver core: make struct class.dev_uevent() take a
 const *

On 11/27/22 05:45, Greg Kroah-Hartman wrote:
> On Fri, Nov 25, 2022 at 03:51:11PM -0800, Bart Van Assche wrote:
>> On 11/23/22 04:25, Greg Kroah-Hartman wrote:
>>> diff --git a/include/linux/mISDNif.h b/include/linux/mISDNif.h
>>> index 7dd1f01ec4f9..7aab4a769736 100644
>>> --- a/include/linux/mISDNif.h
>>> +++ b/include/linux/mISDNif.h
>>> @@ -586,7 +586,7 @@ extern struct mISDNclock *mISDN_register_clock(char *, int, clockctl_func_t *,
>>>    						void *);
>>>    extern void	mISDN_unregister_clock(struct mISDNclock *);
>>> -static inline struct mISDNdevice *dev_to_mISDN(struct device *dev)
>>> +static inline struct mISDNdevice *dev_to_mISDN(const struct device *dev)
>>>    {
>>>    	if (dev)
>>>    		return dev_get_drvdata(dev);
>>
>> Why does the dev_to_mISDN() function drop constness? I haven't found an
>> explanation for this in the cover letter.
> 
> I agree, this is going to be fixed up, see the thread starting here:
> 	https://lore.kernel.org/r/Y34+V2bCDdqujBDk@kroah.com
> 
> I'll work on making a const / non const version for these so that we
> don't loose the marking.
> 
> Oh wait, no, this function is fine, it's not modifying the device
> structure at all, and only returning the pointer in the private data
> stored in the device.  There is no loss of const-ness here.

Hi Greg,

This is what I found in include/linux/mISDNif.h:

struct mISDNdevice {
	struct mISDNchannel	D;
	u_int			id;
	u_int			Dprotocols;
	u_int			Bprotocols;
	u_int			nrbchan;
	u_char			channelmap[MISDN_CHMAP_SIZE];
	struct list_head	bchannels;
	struct mISDNchannel	*teimgr;
	struct device		dev;
};

As one can see 'dev' is a member of struct mISDNdevice. I still think 
that dev_to_mISDN() drops constness. Did I perhaps overlook something?

Bart.