Re: [PATCH 14/20] block: remove the nr_sects field in struct hd_struct

[Jan Kara <jack@xxxxxxx>]

On Wed 18-11-20 09:47:54, Christoph Hellwig wrote:
> Now that the hd_struct always has a block device attached to it, there is
> no need for having two size field that just get out of sync.
> 
> Additional the field in hd_struct did not use proper serializiation,
> possibly allowing for torn writes.  By only using the block_device field
> this problem also gets fixed.
> 
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>

Overall the patch looks good but I have a couple of comments below.

> diff --git a/block/bio.c b/block/bio.c
> index fa01bef35bb1fe..0c5269997434d6 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -613,7 +613,7 @@ void guard_bio_eod(struct bio *bio)
>       rcu_read_lock();
>       part = __disk_get_part(bio->bi_disk, bio->bi_partno);
>       if (part)
> -             maxsector = part_nr_sects_read(part);
> +             maxsector = bdev_nr_sectors(part->bdev);
>       else
>               maxsector = get_capacity(bio->bi_disk);

I have to say that after these changes I find it a bit confusing that we
have get/set_capacity() and bdev_nr_sectors() / bdev_set_nr_sectors() and
they are all the same thing (i_size of the bdev). Is there a reason for the
distinction?

> diff --git a/block/genhd.c b/block/genhd.c
> index 94de95287a6370..e101b6843f7437 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -38,6 +38,16 @@ static void disk_add_events(struct gendisk *disk);
>  static void disk_del_events(struct gendisk *disk);
>  static void disk_release_events(struct gendisk *disk);
>  
> +void set_capacity(struct gendisk *disk, sector_t sectors)
> +{
> +     struct block_device *bdev = disk->part0.bdev;
> +
> +     spin_lock(&bdev->bd_size_lock);
> +     i_size_write(bdev->bd_inode, (loff_t)sectors << SECTOR_SHIFT);
> +     spin_unlock(&bdev->bd_size_lock);

AFAICT bd_size_lock is pointless after these changes so we can just remove
it?

> +}
> +EXPORT_SYMBOL(set_capacity);
> +
>  /*
>   * Set disk capacity and notify if the size is not currently zero and will 
> not
>   * be set to zero.  Returns true if a uevent was sent, otherwise false.
> @@ -47,11 +57,12 @@ bool set_capacity_and_notify(struct gendisk *disk, 
> sector_t size)
>       sector_t capacity = get_capacity(disk);
>  
>       set_capacity(disk, size);
> -     revalidate_disk_size(disk, true);
>  
>       if (capacity != size && capacity != 0 && size != 0) {
>               char *envp[] = { "RESIZE=1", NULL };
>  
> +             pr_info("%s: detected capacity change from %lld to %lld\n",
> +                    disk->disk_name, size, capacity);

So we are now missing above message for transitions from / to 0 capacity?
Is there any other notification in the kernel log when e.g. media is
inserted into a CD-ROM drive? I remember using these messages for detecting
that...

Also what about GENHD_FL_HIDDEN devices? Are we sure we never set capacity
for them?

>               kobject_uevent_env(&disk_to_dev(disk)->kobj, KOBJ_CHANGE, envp);
>               return true;
>       }

...

> @@ -983,7 +994,7 @@ void __init printk_all_partitions(void)
>  
>                       printk("%s%s %10llu %s %s", is_part0 ? "" : "  ",
>                              bdevt_str(part_devt(part), devt_buf),
> -                            (unsigned long long)part_nr_sects_read(part) >> 1
> +                            bdev_nr_sectors(part->bdev) >> 1
>                              , disk_name(disk, part->partno, name_buf),
>                              part->info ? part->info->uuid : "");
>                       if (is_part0) {
> @@ -1076,7 +1087,7 @@ static int show_partition(struct seq_file *seqf, void 
> *v)
>       while ((part = disk_part_iter_next(&piter)))
>               seq_printf(seqf, "%4d  %7d %10llu %s\n",
>                          MAJOR(part_devt(part)), MINOR(part_devt(part)),
> -                        (unsigned long long)part_nr_sects_read(part) >> 1,
> +                        bdev_nr_sectors(part->bdev) >> 1,
>                          disk_name(sgp, part->partno, buf));
>       disk_part_iter_exit(&piter);
>  
> @@ -1158,8 +1169,7 @@ ssize_t part_size_show(struct device *dev,
>  {
>       struct hd_struct *p = dev_to_part(dev);
>  
> -     return sprintf(buf, "%llu\n",
> -             (unsigned long long)part_nr_sects_read(p));
> +     return sprintf(buf, "%llu\n", bdev_nr_sectors(p->bdev));

Is sector_t really guaranteed to be unsigned long long?

                                                                Honza
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR