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

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Message-ID: <132f9c86-5a2b-6770-377a-9323ba344402@acm.org>
Date:   Thu, 17 Mar 2022 20:10:43 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     "yukuai (C)" <yukuai3@...wei.com>, 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

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().

> BTW, do you have any suggestion about patch 3?

I need more time to analyze that patch.

Thanks,

Bart.