linux-kernel - Re: [PATCH] kdev_t: mask mi with MINORMASK in MKDEV macro

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Message-ID: <d890c06e-5b56-629a-2e9f-bc19209238e4@acm.org>
Date:   Fri, 10 Jan 2020 20:50:53 -0800
From:   Bart Van Assche <bvanassche@....org>
To:     Zhiqiang Liu <liuzhiqiang26@...wei.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-block@...r.kernel.org, dhowells@...hat.com,
        akpm@...ux-foundation.org, torvalds@...ux-foundation.org
Cc:     bywxiaobai@....com, Mingfangsen <mingfangsen@...wei.com>,
        Guiyao <guiyao@...wei.com>, zhangsaisai <zhangsaisai@...wei.com>,
        renxudong <renxudong1@...wei.com>
Subject: Re: [PATCH] kdev_t: mask mi with MINORMASK in MKDEV macro

On 2020-01-09 22:37, Zhiqiang Liu wrote:
> 
> In MKDEV macro, if mi is larger than MINORMASK, the major will be
> affected by mi. For example, set dev = MKDEV(2, (1U << MINORBITS)),
> then MAJOR(dev) will be equal to 3, incorrectly.
> 
> Here, we mask mi with MINORMASK in MKDEV macro.
> 
> Signed-off-by: Zhiqiang Liu <liuzhiqiang26@...wei.com>
> ---
>  include/linux/kdev_t.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/kdev_t.h b/include/linux/kdev_t.h
> index 85b5151911cf..40a9423720b2 100644
> --- a/include/linux/kdev_t.h
> +++ b/include/linux/kdev_t.h
> @@ -9,7 +9,7 @@
> 
>  #define MAJOR(dev)	((unsigned int) ((dev) >> MINORBITS))
>  #define MINOR(dev)	((unsigned int) ((dev) & MINORMASK))
> -#define MKDEV(ma,mi)	(((ma) << MINORBITS) | (mi))
> +#define MKDEV(ma, mi)	(((ma) << MINORBITS) | ((mi) & MINORMASK))
> 
>  #define print_dev_t(buffer, dev)					\
>  	sprintf((buffer), "%u:%u\n", MAJOR(dev), MINOR(dev))

Shouldn't the users of MKDEV() be fixed instead of changing the MKDEV()
definition?

Thanks,

Bart.