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

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Message-Id: <20131101123041.d08adc9739cf6e733d822770@linux-foundation.org>
Date:	Fri, 1 Nov 2013 12:30:41 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Evgeniy Polyakov <zbr@...emap.net>
Cc:	Michal Nazarewicz <mina86@...a86.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drivers: w1: make w1_slave::flags long to avoid casts

On Fri, 01 Nov 2013 20:01:39 +0400 Evgeniy Polyakov <zbr@...emap.net> wrote:

> > Now that I look at documentation, I think you are correct, but the
> > problem is on big-endian 64-bit architectures. __The fix is still
> > valid, but the commit message not so much. __Something along the
> > lines of the following would be better:
> 
> Guys, you so much overcomplicate things - this field is basically a set of in-memory flags
> for attached device, there is no need to even think about how it is present in different endianess
> 
> Or do I miss something fundamental there? I wrote it gazillions years ago and probably already forgot something

set_bit() operates on longs.  So if we do

struct foo {
	u32 a;
	u32 b;
} f;

	...
	set_bit(0, (long *)&f.a);
	...

then we'll scribble on f.b on a big-endian 64-bit machine.
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