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

[yukuai (C)]

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@xxxxxxxxxx>
> > > > ---
> > > >   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