Re: [PATCH 1/2] super1.0 calculates max sectors in a wrong way

[Song Liu <song@kernel.org>]

On Tue, Jun 30, 2020 at 12:55 AM Xiao Ni <xni@redhat.com> wrote:
>
> One super1.0 raid array wants to grow size, it needs to check the device max usable
> size. If the requested size is bigger than max usable size, it will return an error.
>
> Now it uses rdev->sectors for max usable size. If one disk is 500G and the raid device
> only uses the 100GB of this disk. rdev->sectors can't tell the real max usable size.
> The max usable size should be dev_size-(superblock_size+bitmap_size+badblock_size).
>
> Signed-off-by: Xiao Ni <xni@redhat.com>

Thanks for the fix!

> ---
>  drivers/md/md.c | 26 +++++++++++++++++++++++---
>  1 file changed, 23 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index f567f53..d2c5984 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -2183,10 +2183,30 @@ super_1_rdev_size_change(struct md_rdev *rdev, sector_t num_sectors)
>                 return 0;
>         } else {
>                 /* minor version 0; superblock after data */
> -               sector_t sb_start;
> -               sb_start = (i_size_read(rdev->bdev->bd_inode) >> 9) - 8*2;
> +               sector_t sb_start, bm_space;
> +               sector_t dev_size = i_size_read(rdev->bdev->bd_inode) >> 9;
> +
> +               /* 8K is for superblock */
> +               sb_start = dev_size - 8*2;
>                 sb_start &= ~(sector_t)(4*2 - 1);
> -               max_sectors = rdev->sectors + sb_start - rdev->sb_start;
> +
> +               /* if the device is bigger than 8Gig, save 64k for bitmap usage,
> +                * if bigger than 200Gig, save 128k
> +                */
> +               if (dev_size < 64*2)
> +                       bm_space = 0;
> +               else if (dev_size - 64*2 >= 200*1024*1024*2)
> +                       bm_space = 128*2;
> +               else if (dev_size - 4*2 > 8*1024*1024*2)
> +                       bm_space = 64*2;
> +               else
> +                       bm_space = 4*2;

Could you explain the handling of bitmap space?

Thanks,
Song