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

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Date:   Wed, 17 Mar 2021 08:02:40 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Menglong Dong <menglong8.dong@...il.com>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        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 09:53:23PM +0800, Menglong Dong wrote:
> 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.

Also, flags is used in several other functions, not just recvmsg.

> This patch is already reverted, and I think maybe
> I can resend it after I fix these 'int' flags.

I would suggest to consult with Dave on that. While much of the conversion
could be handled automatically with coccinelle, it touches a lot of files.
I don't think that is worth the effort (or risk).

Guenter