Re: [PATCH v3 2/2] md: simplify md_seq_ops

[Yu Kuai]

Hi,

在 2024/01/09 16:12, Song Liu 写道:
> On Mon, Jan 8, 2024 at 11:48 PM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
> > Hi,
> >
> > 在 2024/01/09 9:21, Yu Kuai 写道:
> > > Hi,
> > >
> > > 在 2024/01/09 7:38, Song Liu 写道:
> > > > On Tue, Sep 26, 2023 at 11:19 PM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
> [...]
> > diff --git a/drivers/md/md.c b/drivers/md/md.c
> > index e351e6c51cc7..289d3d89e73d 100644
> > --- a/drivers/md/md.c
> > +++ b/drivers/md/md.c
> > @@ -8135,6 +8135,19 @@ static void status_unused(struct seq_file *seq)
> >           seq_printf(seq, "\n");
> >    }
> >
> > +static void status_personalities(struct seq_file *seq)
> > +{
> > +       struct md_personality *pers;
> > +
> > +       seq_puts(seq, "Personalities : ");
> > +       spin_lock(&pers_lock);
> > +       list_for_each_entry(pers, &pers_list, list)
> > +               seq_printf(seq, "[%s] ", pers->name);
> > +
> > +       spin_unlock(&pers_lock);
> > +       seq_puts(seq, "\n");
> > +}
> > +
> >    static int status_resync(struct seq_file *seq, struct mddev *mddev)
> >    {
> >           sector_t max_sectors, resync, res;
> > @@ -8273,43 +8286,53 @@ static int status_resync(struct seq_file *seq,
> > struct mddev *mddev)
> >           return 1;
> >    }
> >
> > +#define MDDEV_NONE (void *)1
> > +
> >    static void *md_seq_start(struct seq_file *seq, loff_t *pos)
> >           __acquires(&all_mddevs_lock)
> >    {
> > -       struct md_personality *pers;
> > -
> > -       seq_puts(seq, "Personalities : ");
> > -       spin_lock(&pers_lock);
> > -       list_for_each_entry(pers, &pers_list, list)
> > -               seq_printf(seq, "[%s] ", pers->name);
> > -
> > -       spin_unlock(&pers_lock);
> > -       seq_puts(seq, "\n");
> >           seq->poll_event = atomic_read(&md_event_count);
> > -
> >           spin_lock(&all_mddevs_lock);
> >
> > -       return seq_list_start(&all_mddevs, *pos);
> > +       if (!list_empty(&all_mddevs))
> > +               return seq_list_start(&all_mddevs, *pos);
> > +       else if (*pos == 0)
> > +               return MDDEV_NONE;
> > +       else
> > +               return NULL;
> >    }
> >
> >    static void *md_seq_next(struct seq_file *seq, void *v, loff_t *pos)
> >    {
> > +       if (v == MDDEV_NONE) {
> > +               ++*pos;
> > +               return NULL;
> > +       }
> > +
> >           return seq_list_next(v, &all_mddevs, pos);
> >    }
> >
> >    static void md_seq_stop(struct seq_file *seq, void *v)
> >           __releases(&all_mddevs_lock)
> >    {
> > -       status_unused(seq);
> >           spin_unlock(&all_mddevs_lock);
> >    }
> >    static int md_seq_show(struct seq_file *seq, void *v)
> >    {
> > -       struct mddev *mddev = list_entry(v, struct mddev, all_mddevs);
> > +       struct mddev *mddev;
> >           sector_t sectors;
> >           struct md_rdev *rdev;
> >
> > +       if (v == MDDEV_NONE) {
> > +               status_personalities(seq);
> > +               status_unused(seq);
> > +               return 0;
> > +       }
> > +
> > +       mddev = list_entry(v, struct mddev, all_mddevs);
> > +       if (mddev == list_first_entry(&all_mddevs, struct mddev,
> > all_mddevs))
> > +               status_personalities(seq);
> >           if (!mddev_get(mddev))
> >                   return 0;
> >
> > @@ -8385,6 +8408,10 @@ static int md_seq_show(struct seq_file *seq, void *v)
> >           }
> >           spin_unlock(&mddev->lock);
> >           spin_lock(&all_mddevs_lock);
> > +
> > +       if (mddev == list_last_entry(&all_mddevs, struct mddev, all_mddevs))
> > +               status_unused(seq);
> > +
> >           if (atomic_dec_and_test(&mddev->active))
> >                   __mddev_put(mddev);
>
> I think something like the following is the right way to do this.
>
> Thanks,
> Song
>
> diff --git i/drivers/md/md.c w/drivers/md/md.c
> index 38a6767c65b1..14044febe009 100644
> --- i/drivers/md/md.c
> +++ w/drivers/md/md.c
> @@ -8215,20 +8215,8 @@ static int status_resync(struct seq_file *seq,
> struct mddev *mddev)
>   static void *md_seq_start(struct seq_file *seq, loff_t *pos)
>          __acquires(&all_mddevs_lock)
>   {
> -       struct md_personality *pers;
> -
> -       seq_puts(seq, "Personalities : ");
> -       spin_lock(&pers_lock);
> -       list_for_each_entry(pers, &pers_list, list)
> -               seq_printf(seq, "[%s] ", pers->name);
> -
> -       spin_unlock(&pers_lock);
> -       seq_puts(seq, "\n");
> -       seq->poll_event = atomic_read(&md_event_count);
> -
>          spin_lock(&all_mddevs_lock);
> -
> -       return seq_list_start(&all_mddevs, *pos);
> +       return seq_list_start_head(&all_mddevs, *pos);

Yes, this is good. I didn't notice the api seq_list_start_head().
>   }
>
>   static void *md_seq_next(struct seq_file *seq, void *v, loff_t *pos)
> @@ -8243,12 +8231,31 @@ static void md_seq_stop(struct seq_file *seq, void *v)
>          spin_unlock(&all_mddevs_lock);
>   }
>
> +static void md_seq_print_header(struct seq_file *seq)
> +{
> +       struct md_personality *pers;
> +
> +       seq_puts(seq, "Personalities : ");
> +       spin_lock(&pers_lock);
> +       list_for_each_entry(pers, &pers_list, list)
> +               seq_printf(seq, "[%s] ", pers->name);
> +
> +       spin_unlock(&pers_lock);
> +       seq_puts(seq, "\n");
> +       seq->poll_event = atomic_read(&md_event_count);
> +}
> +
>   static int md_seq_show(struct seq_file *seq, void *v)
>   {
>          struct mddev *mddev = list_entry(v, struct mddev, all_mddevs);
>          sector_t sectors;
>          struct md_rdev *rdev;
>
> +       if (v == &all_mddevs) {
> +               md_seq_print_header(seq);

And I will still move status_unused() to md_seq_show(), because 
seq_read_iter() only handle the case that seq_printf() overflowed from
md_seq_show(), not md_seq_start/stop().

Thanks,
Kuai

> +               return 0;
> +       }
> +
>          if (!mddev_get(mddev))
>                  return 0;
>
> .