linux-kernel - Re: [PATCH] block: uapi: Fix compliation warning of using IOPRIO_PRIO

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Date: Fri, 31 May 2024 13:13:07 -0700
From: Bart Van Assche <bvanassche@....org>
To: Zhiguo Niu <zhiguo.niu@...soc.com>, axboe@...nel.dk
Cc: dlemoal@...nel.org, linux-kernel@...r.kernel.org, niuzhiguo84@...il.com,
 ke.wang@...soc.com
Subject: Re: [PATCH] block: uapi: Fix compliation warning of using
 IOPRIO_PRIO_DATA

On 5/31/24 04:31, Zhiguo Niu wrote:
> Generally, the input of IOPRIO_PRIO_DATA has 16 bits. If use format "%d"
> to printk IOPRIO_PRIO_DATA, there will be the following warning or error.
> 
> fs/f2fs/sysfs.c:348:31: warning: format ‘%d’ expects argument of type ‘int’, but argument 4 has type ‘long unsigned int’ [-Wformat=]
>     return sysfs_emit(buf, "%s,%d\n",
>                                ~^
>                                %ld
> 
> This is because the output of IOPRIO_PRIO_DATA is converted to "UL" from
> IOPRIO_PRIO_MASK, which is not reasonable. unsigned int is more suitable.
> 
> Signed-off-by: Zhiguo Niu <zhiguo.niu@...soc.com>
> ---
>   include/uapi/linux/ioprio.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/uapi/linux/ioprio.h b/include/uapi/linux/ioprio.h
> index bee2bdb0..9ead07f 100644
> --- a/include/uapi/linux/ioprio.h
> +++ b/include/uapi/linux/ioprio.h
> @@ -11,7 +11,7 @@
>   #define IOPRIO_CLASS_SHIFT	13
>   #define IOPRIO_NR_CLASSES	8
>   #define IOPRIO_CLASS_MASK	(IOPRIO_NR_CLASSES - 1)
> -#define IOPRIO_PRIO_MASK	((1UL << IOPRIO_CLASS_SHIFT) - 1)
> +#define IOPRIO_PRIO_MASK	((1U << IOPRIO_CLASS_SHIFT) - 1)
>   
>   #define IOPRIO_PRIO_CLASS(ioprio)	\
>   	(((ioprio) >> IOPRIO_CLASS_SHIFT) & IOPRIO_CLASS_MASK)

This change is safe even if the mask is applied to an expression with more bits
than an int because of the integer promotion rules. Hence:

Reviewed-by: Bart Van Assche <bvanassche@....org>