linux-kernel - Re: [PATCH] bitops: Introduce BITS_PER

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Date:   Fri, 6 Jul 2018 10:55:57 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Chris Wilson <chris@...is-wilson.co.uk>,
        linux-kernel@...r.kernel.org
Cc:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Andy Gospodarek <gospo@...adcom.com>,
        "David S . Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] bitops: Introduce BITS_PER_TYPE

On 07/06/18 10:51, Chris Wilson wrote:
> Quoting Randy Dunlap (2018-07-06 18:48:55)
>>
>> On 07/06/18 02:44, Chris Wilson wrote:
>>> net_dim.h has a rather useful extension to BITS_PER_BYTE to compute the
>>> number of bits in a type (BITS_PER_BYTE * sizeof(T)), so promote the
>>> macro to bitops.h, alongside BITS_PER_BYTE, for wider usage.
>>>
>>> Signed-off-by: Chris Wilson <chris@...is-wilson.co.uk>
>>> Cc: Jani Nikula <jani.nikula@...ux.intel.com>
>>> Cc: Andy Gospodarek <gospo@...adcom.com>
>>> Cc: David S. Miller <davem@...emloft.net>
>>> Cc: Thomas Gleixner <tglx@...utronix.de>
>>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>>> Cc: Ingo Molnar <mingo@...nel.org>
>>> ---
>>>  include/linux/bitops.h  | 3 ++-
>>>  include/linux/net_dim.h | 1 -
>>>  2 files changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/include/linux/bitops.h b/include/linux/bitops.h
>>> index 4cac4e1a72ff..091cb17d1a9b 100644
>>> --- a/include/linux/bitops.h
>>> +++ b/include/linux/bitops.h
>>> @@ -11,7 +11,8 @@
>>>  #define BIT_ULL_MASK(nr)     (1ULL << ((nr) % BITS_PER_LONG_LONG))
>>>  #define BIT_ULL_WORD(nr)     ((nr) / BITS_PER_LONG_LONG)
>>>  #define BITS_PER_BYTE                8
>>> -#define BITS_TO_LONGS(nr)    DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(long))
>>> +#define BITS_PER_TYPE(type) (sizeof(type) * BITS_PER_BYTE)
>>> +#define BITS_TO_LONGS(nr)    DIV_ROUND_UP(nr, BITS_PER_TYPE(long))
>>>  #endif
>>>  
>>>  /*
>>
>> doesn't <linux/net_dim.h> need to #include <linux/bitops.h> ?
> 
> It already has to in order to obtain BITS_PER_BYTE. Just doesn't do so
> directly.

Right.  and does that work on all $ARCHes?

Please see Documentation/process/submit-checklist.rst, rule #1:
1) If you use a facility then #include the file that defines/declares
   that facility.  Don't depend on other header files pulling in ones
   that you use.


thanks,
-- 
~Randy