Re: [Qemu-devel] [[PATCH v2] 1/1] vpc.c: Add VHD resize support

[Stefan Hajnoczi]

On Mon, Sep 22, 2014 at 01:24:16PM +0000, Lucian Petrut wrote:
>  >> +    if (cpu_to_be32(footer->type) == VHD_DIFFERENCING) {
>  >footer_buf is big-endian so this should be be32_to_cpu()
> 
> My bad, I’ll fix the BE related issues.

The existing block/vpc.c code confuses beX_to_cpu() and cpu_to_beX().  I
have sent a patch to fix that ("[PATCH] vpc: fix beX_to_cpu() and
cpu_to_beX() confusion").

>  >> +        error_report("Resizing differencing vhd images is not 
> supported.");
>  >> +        return -ENOTSUP;
>  >> +    }
>  >> +
>  >> +    old_bat_size = (s->max_table_entries * 4 + 511) & ~511;
>  >> +    new_total_sectors = offset / BDRV_SECTOR_SIZE;
>  >> +
>  >> +    for (index = 0; new_total_sectors > (int64_t)cyls * heads * 
> secs_per_cyl;
>  >> +            index++) {
>  >> +        if (calculate_geometry(new_total_sectors + index, &cyls, &heads,
>  >> +                               &secs_per_cyl)) {
>  >> +            return -EFBIG;
>  >> +        }
>  >> +    }
>  >> +    new_total_sectors = (int64_t) cyls * heads * secs_per_cyl;
>  >> +    new_num_bat_entries = (new_total_sectors + s->block_size / 512) /
>  >> +                          (s->block_size / 512);
>  >This expression doesn't just round up, it always adds an extra block.
>  >Is this intentional?
>  >I expected the numerator for rounding up to be:
>  >  new_total_sectors + s->block_size / 512 - 1
> 
> This was intended, it may just add an extra entry. Also, the number
> of entries is calculated in the same way in the existing code which
> creates dynamic VHDs, so I wanted to keep consistency with that
> as well.

Okay, if existing code already does it like this it makes sense to be
consistent.

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