linux-kernel - Re: [PATCH net-next 2/2] net: socket: change MSG_CMSG

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Date:   Sun, 21 Mar 2021 23:49:06 +1100
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     menglong8.dong@...il.com
Cc:     andy.shevchenko@...il.com, kuba@...nel.org, linux@...ck-us.net,
        David.Laight@...lab.com, davem@...emloft.net,
        dong.menglong@....com.cn, viro@...iv.linux.org.uk, axboe@...nel.dk,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 2/2] net: socket: change MSG_CMSG_COMPAT to
 BIT(21)

On Sun, Mar 21, 2021 at 08:39:29PM +0800, menglong8.dong@...il.com wrote:
>
> diff --git a/include/linux/socket.h b/include/linux/socket.h
> index d5ebfe30d96b..317b2933f499 100644
> --- a/include/linux/socket.h
> +++ b/include/linux/socket.h
> @@ -312,17 +312,18 @@ struct ucred {
>  					 * plain text and require encryption
>  					 */
>  
> +#if defined(CONFIG_COMPAT)
> +#define MSG_CMSG_COMPAT		BIT(21)	/* This message needs 32 bit fixups */
> +#else
> +#define MSG_CMSG_COMPAT		0	/* We never have 32 bit fixups */
> +#endif
> +
>  #define MSG_ZEROCOPY		BIT(26)	/* Use user data in kernel path */
>  #define MSG_FASTOPEN		BIT(29)	/* Send data in TCP SYN */
>  #define MSG_CMSG_CLOEXEC	BIT(30)	/* Set close_on_exec for file
>  					 * descriptor received through
>  					 * SCM_RIGHTS
>  					 */
> -#if defined(CONFIG_COMPAT)
> -#define MSG_CMSG_COMPAT		BIT(31)	/* This message needs 32 bit fixups */
> -#else
> -#define MSG_CMSG_COMPAT		0	/* We never have 32 bit fixups */
> -#endif

Shouldn't you add some comment here to stop people from trying to
use BIT(31) in the future?

Thanks,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt