linux-kernel - Re: [PATCH] tcp: Use BIT() for OPTION

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Date:   Thu, 4 Nov 2021 09:38:26 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     David Laight <David.Laight@...LAB.COM>,
        'Eric Dumazet' <eric.dumazet@...il.com>,
        Leonard Crestez <cdleonard@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        David Ahern <dsahern@...nel.org>
Cc:     Dmitry Safonov <0x7f454c46@...il.com>,
        Kuniyuki Iwashima <kuniyu@...zon.co.jp>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Neal Cardwell <ncardwell@...gle.com>,
        Yuchung Cheng <ycheng@...gle.com>,
        Enke Chen <enchen@...oaltonetworks.com>,
        Wei Wang <weiwan@...gle.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tcp: Use BIT() for OPTION_* constants



On 11/4/21 2:17 AM, David Laight wrote:
> From: Eric Dumazet
>> Sent: 03 November 2021 22:50
>>
>> On 11/3/21 3:17 PM, Leonard Crestez wrote:
>>> Extending these flags using the existing (1 << x) pattern triggers
>>> complaints from checkpatch. Instead of ignoring checkpatch modify the
>>> existing values to use BIT(x) style in a separate commit.
>>>
>>> Signed-off-by: Leonard Crestez <cdleonard@...il.com>
>>>
>>
>> Yes, I guess checkpatch does not know that we currently use at most 16 bits :)
>>
>> u16 options = opts->options;
>>
>> Anyway, this seems fine.
> 
> Doesn't BIT() have a nasty habit of generating 64bit constants
> that just cause a different set of issues when inverted?
> It may be safe here - but who knows.

BIT() does not use/force 64bit constants, plain "unsigned long" ones.

Really this patch looks a nop to me.