linux-kernel - Re: [PATCH V3] block: uapi: Use unsigned int type for IOPRIO_PRIO

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Message-ID: <CAHJ8P3K6sN2_pNWUNc3C0XhLZJfmFnN7gzC7N70U2M4w6MgJPg@mail.gmail.com>
Date: Wed, 31 Jul 2024 19:07:39 +0800
From: Zhiguo Niu <niuzhiguo84@...il.com>
To: Damien Le Moal <dlemoal@...nel.org>
Cc: Zhiguo Niu <zhiguo.niu@...soc.com>, axboe@...nel.dk, hch@....de, bvanassche@....org, 
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, ke.wang@...soc.com, 
	Hao_hao.Wang@...soc.com
Subject: Re: [PATCH V3] block: uapi: Use unsigned int type for IOPRIO_PRIO_MASK

Hi Damien Le Moal

Damien Le Moal <dlemoal@...nel.org> 于2024年7月31日周三 17:28写道：
>
> On 7/31/24 16:01, Zhiguo Niu wrote:
> > Generally, the input of IOPRIO_PRIO_DATA has 16 bits, but the output of
> > IOPRIO_PRIO_DATA will be expanded to "UL" from IOPRIO_PRIO_MASK.
> >  #define IOPRIO_PRIO_MASK     ((1UL << IOPRIO_CLASS_SHIFT) - 1)
> > This is not reasonable and meaningless, unsigned int is more suitable for it.
> >
> > So if use format "%d" to print IOPRIO_PRIO_DATA directly, theire will be a
> > build warning or error showned as the following, which is from the
> > local test when I modify f2fs codes.
> >
> > 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
> >
> > When modules use IOPRIO_PRIO_CLASS & IOPRIO_PRIO_LEVEL get ioprio's class and
> > level, their outputs are both unsigned int.
> >  IOPRIO_CLASS_MASK is:
> >  #define IOPRIO_CLASS_SHIFT   13
> >  #define IOPRIO_NR_CLASSES    8
> >  #define IOPRIO_CLASS_MASK    (IOPRIO_NR_CLASSES - 1)
> >  IOPRIO_LEVEL_MASK is:
> >  #define IOPRIO_LEVEL_NR_BITS 3
> >  #define IOPRIO_NR_LEVELS     (1 << IOPRIO_LEVEL_NR_BITS)
> >  #define IOPRIO_LEVEL_MASK    (IOPRIO_NR_LEVELS - 1)
> >
> > Ioprio is passed along as an int internally, so we should not be using an
> > unsigned long for IOPRIO_PRIO_MASK to not end up with IOPRIO_PRIO_DATA
> > returning an unsigned long as well.
>
> I would write this commit message like this:
>
>
> An ioprio is passed internally as an int value. When IOPRIO_PRIO_CLASS() and
> IOPRIO_PRIO_LEVEL() are used to extract from it the priority class and level,
> the values obtained are thus also int.
> However, the IOPRIO_PRIO_MASK() macro used to define the IOPRIO_PRIO_DATA()
> macro is defined as:
>
> #define IOPRIO_PRIO_MASK        ((1UL << IOPRIO_CLASS_SHIFT) - 1)
>
> that is, the macro gives an unsigned long value, which leads to
> IOPRIO_PRIO_DATA() also returning an unsigned long.
>
> Make things consistent between class, level and data and use int everywhere by
> removing forced unsigned long from IOPRIO_PRIO_MASK.

Thank you for your professional advice and sharing. I will update this.

>
>
>
> --
> Damien Le Moal
> Western Digital Research
>