linux-kernel - Re: [PATCH] drivers: w1: make w1_slave::flags long to avoid casts

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Date:	Wed, 30 Oct 2013 15:59:38 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Michal Nazarewicz <mpn@...gle.com>
Cc:	Evgeniy Polyakov <zbr@...emap.net>, linux-kernel@...r.kernel.org,
	Michal Nazarewicz <mina86@...a86.com>
Subject: Re: [PATCH] drivers: w1: make w1_slave::flags long to avoid casts

On Sat, 26 Oct 2013 12:56:11 +0100 Michal Nazarewicz <mpn@...gle.com> wrote:

> From: Michal Nazarewicz <mina86@...a86.com>
> 
> Changing flags field of the w1_slave to unsigned long may on
> some architectures increase the size of the structure, but
> otherwise makes the code more kosher as casting is avoided
> and *_bit family of calls do not attempt to operate on an
> entity of bigger size than realy is available.
> 
> The current behaviour does not introduce any bugs (since any
> bytes past flags field are preserved)

hm, what does this mean....

> --- a/drivers/w1/w1.c
> +++ b/drivers/w1/w1.c
> @@ -709,7 +709,7 @@ static int w1_attach_slave_device(struct w1_master *dev, struct w1_reg_num *rn)
>  
>  	sl->owner = THIS_MODULE;
>  	sl->master = dev;
> -	set_bit(W1_SLAVE_ACTIVE, (long *)&sl->flags);
> +	set_bit(W1_SLAVE_ACTIVE, &sl->flags);

...  I'd have though that running this code on little-endian 64-bit
would result in a scribble over ...

> --- a/drivers/w1/w1.h
> +++ b/drivers/w1/w1.h
> @@ -67,8 +67,8 @@ struct w1_slave
>  	struct w1_reg_num	reg_num;
>  	atomic_t		refcnt;
>  	u8			rom[9];
> -	u32			flags;
>  	int			ttl;

... w1_slave.ttl?

> +	unsigned long		flags;
>  
>  	struct w1_master	*master;
>  	struct w1_family	*family;
>
> ...
>
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