linux-kernel - Re: [PATCHv3 04/10] linux/kernel: introduce lower_48

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Message-ID: <38d356c2ea0cd9c8cec1e6377793b5c465eca889.camel@perches.com>
Date:   Tue, 22 Feb 2022 08:58:56 -0800
From:   Joe Perches <joe@...ches.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Keith Busch <kbusch@...nel.org>, linux-nvme@...ts.infradead.org,
        linux-block@...r.kernel.org, linux-crypto@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org, axboe@...nel.dk,
        martin.petersen@...cle.com, colyli@...e.de,
        Bart Van Assche <bvanassche@....org>
Subject: Re: [PATCHv3 04/10] linux/kernel: introduce lower_48_bits macro

On Tue, 2022-02-22 at 17:50 +0100, Christoph Hellwig wrote:
> On Tue, Feb 22, 2022 at 08:45:53AM -0800, Joe Perches wrote:
> > On Tue, 2022-02-22 at 08:31 -0800, Keith Busch wrote:
> > > Recent data integrity field enhancements allow 48-bit reference tags.
> > > Introduce a helper macro since this will be a repeated operation.
> > []
> > > diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> > []
> > > @@ -63,6 +63,12 @@
> > >  }					\
> > >  )
> > >  
> > > +/**
> > > + * lower_48_bits - return bits 0-47 of a number
> > > + * @n: the number we're accessing
> > > + */
> > > +#define lower_48_bits(n) ((u64)((n) & 0xffffffffffffull))
> > 
> > why not make this a static inline function?
> 
> Agreed.
> 
> > And visually, it's difficult to quickly count a repeated character to 12.
> > 
> > Perhaps:
> > 
> > static inline u64 lower_48_bits(u64 val)
> > {
> > 	return val & GENMASK_ULL(47, 0);
> > }
> 
> For anyone who has a minimum knowledge of C and hardware your version
> is an obsfucated clusterfuck, while the version Keith wrote is
> trivial to read.

Don't think so.  I've dealt with hardware and have more than once
seen defects introduced by firmware developers that can't count.

be quick, which one is it:

	0xfffffffffffULL
or
	0xffffffffffffULL
or
	0xfffffffffffffULL
or
	0xffffffffffffffULL