linux-kernel - Re: [RFC PATCH 3/3] Convert mce

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Message-ID: <20121012215859.GA18739@aftab.osrc.amd.com>
Date:	Fri, 12 Oct 2012 23:58:59 +0200
From:	Borislav Petkov <bp@...64.org>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Borislav Petkov <borislav.petkov@....com>
Subject: Re: [RFC PATCH 3/3] Convert mce_disabled

On Fri, Oct 12, 2012 at 05:46:16PM +0000, Luck, Tony wrote:
> > Or, you can modify the mca_config I have there and use bools and pass a
> > pointer to each actual bool member in each DEVICE_BIT_ATTR invocation
> > (and rename it to DEVICE_BOOL_ATTR). Yeah, that could work, unless I'm
> > missing something else, of course.
> 
> This looks like the best solution to me. Sure we use a little more memory for
> a "bool" for each option instead of just a single bit. But there are only a
> handful of them, not thousands. So I think we can cope with a few extra
> bytes of memory consumption.  I was still not completely convinced by the
> 
>        if (val)
>                *bvec |= le64_to_cpu(BIT_64(bit));
> 
> solution - it assumes that big endian machines also assign their bit numbers
> in a big->little way - but that isn't required by the C standard. bitfields are
> assigned at the whim of the compiler writer (the only restrictions seem to
> be on alignments of fields w.r.t. to the underlying data types).

Ok, it seems that would've been a can of worms if we'd opened it.

Fortunately, if we do bools and we pass a pointer to the respective bool
member of mca_config, we won't need to do that anymore. Instead simply:

	*bool_ptr = !!val;

It can't get any simpler than that. I'll give it a try soon to see
whether it pans out as I'm imagining it.

Thanks.


-- 
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Boris.

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