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

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Date:   Tue, 22 Feb 2022 17:50:45 +0100
From:   Christoph Hellwig <hch@....de>
To:     Joe Perches <joe@...ches.com>
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,
        hch@....de, 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, 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.