linux-kernel - Re: [PATCH v4 RESEND net-next] net: socket: use BIT() for MSG

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Date:   Wed, 17 Mar 2021 21:53:23 +0800
From:   Menglong Dong <menglong8.dong@...il.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Guenter Roeck <linux@...ck-us.net>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
        "dong.menglong@....com.cn" <dong.menglong@....com.cn>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH v4 RESEND net-next] net: socket: use BIT() for MSG_*

On Wed, Mar 17, 2021 at 5:36 PM Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
>
...
>
> The problematic code is negation of the flags when it's done in
> operations like &.
> It maybe fixed by swapping positions of the arguments, i.e. ~(FOO |
> BAR) & flags.
>
> All this is a beast called "integer promotions" in the C standard.
>
> The best is to try to get flags to be unsigned. By how invasive it may be?

Seems that the inconsistent usages of 'msg_flags' is a lot, for example the
'recvmsg()' in 'struct proto' and 'recvmsg()' in 'struct proto_ops':

int (*recvmsg)(struct sock *sk, struct msghdr *msg,
        size_t len, int noblock, int flags,
        int *addr_len);

This function prototype is used in many places, It's not easy to fix them.
This patch is already reverted, and I think maybe
I can resend it after I fix these 'int' flags.

>
> --
> With Best Regards,
> Andy Shevchenko

Thanks!
Menglong Dong