linux-kernel - Re: [PATCH 1/3] block: don't show disk stats if io accounting is disabled

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Date:   Fri, 18 Mar 2022 14:12:19 +0800
From:   "yukuai (C)" <yukuai3@...wei.com>
To:     Bart Van Assche <bvanassche@....org>, <axboe@...nel.dk>,
        <mpatocka@...hat.com>, <snitzer@...hat.com>
CC:     <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <yi.zhang@...wei.com>
Subject: Re: [PATCH 1/3] block: don't show disk stats if io accounting is
 disabled

在 2022/03/18 11:10, Bart Van Assche 写道:
> On 3/17/22 18:36, yukuai (C) wrote:
>> 在 2022/03/17 22:06, Bart Van Assche 写道:
>>> On 3/17/22 04:26, Yu Kuai wrote:
>>>> If io accounting is disabled, there is no point to handle such device
>>>> in diskstats_show(), and it can be confused for users because all 
>>>> fields
>>>> in iostat are zero while the disk is handling io.
>>>>
>>>> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
>>>> ---
>>>>   block/genhd.c | 5 +++++
>>>>   1 file changed, 5 insertions(+)
>>>>
>>>> diff --git a/block/genhd.c b/block/genhd.c
>>>> index c3b32c665aec..e5307f512185 100644
>>>> --- a/block/genhd.c
>>>> +++ b/block/genhd.c
>>>> @@ -937,6 +937,9 @@ ssize_t part_stat_show(struct device *dev,
>>>>       struct disk_stats stat;
>>>>       unsigned int inflight;
>>>> +    if (!blk_queue_io_stat(q))
>>>> +        return sprintf(buf, "io accounting is disabled\n");
>>>> +
>>>
>>> Hmm ... the above looks sub-optimal to me. Has it been considered to 
>>> return an error code instead or even better to hide the stat 
>>> attribute if I/O accounting is disabled? The latter can be achieved 
>>> by modifying disk_visible().
>  >
>> It's right this way is much better, i'll hide the 'stat' in next
>> iteration.
> 
> Please note that modifying disk_visible() only is not sufficient. 
> sysfs_update_group() needs to be called to trigger a call to 
> disk_visible() if a variable has changed that affects the return value 
> of disk_visible().

Hi,

Thanks for your advice, I wonder can the queue flag
'QUEUE_FLAG_IO_STAT' change after the disk is created? I don't
see it can change anywhere. In this case, perhaps we don't need
to consider calling sysfs_update_group().

> 
>> BTW, do you have any suggestion about patch 3?
> 
> I need more time to analyze that patch.

Thanks for sending time on the patch.

Kuai