Re: [RFC PATCH v2 10/26] qcow2: Update get/set_l2_entry() and add get/set_l2_bitmap()

[Max Reitz <mreitz@redhat.com>]

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On 26.10.19 23:25, Alberto Garcia wrote:
> Extended L2 entries are 128-bit wide: 64 bits for the entry itself and
> 64 bits for the subcluster allocation bitmap.
> 
> In order to support them correctly get/set_l2_entry() need to be
> updated so they take the entry width into account in order to
> calculate the correct offset.
> 
> This patch also adds the get/set_l2_bitmap() functions that are used
> to access the bitmaps. For convenience, these functions are no-ops
> when used in traditional qcow2 images.

Granted, I haven’t seen the following patches yet, but if these
functions are indeed called for images that don’t have subclusters,
shouldn’t they return 0x0*0f*f then? (i.e. everything allocated)

If they aren’t, they should probably just abort().  Well,
set_l2_bitmap() should probably always abort() if there aren’t any
subclusters.

Max

> Signed-off-by: Alberto Garcia <berto@igalia.com>
> ---
>  block/qcow2.h | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/block/qcow2.h b/block/qcow2.h
> index 29a253bfb9..741c41c80f 100644
> --- a/block/qcow2.h
> +++ b/block/qcow2.h
> @@ -507,15 +507,37 @@ static inline size_t l2_entry_size(BDRVQcow2State *s)
>  static inline uint64_t get_l2_entry(BDRVQcow2State *s, uint64_t *l2_slice,
>                                      int idx)
>  {
> +    idx *= l2_entry_size(s) / sizeof(uint64_t);
>      return be64_to_cpu(l2_slice[idx]);
>  }
>  
> +static inline uint64_t get_l2_bitmap(BDRVQcow2State *s, uint64_t *l2_slice,
> +                                     int idx)
> +{
> +    if (has_subclusters(s)) {
> +        idx *= l2_entry_size(s) / sizeof(uint64_t);
> +        return be64_to_cpu(l2_slice[idx + 1]);
> +    } else {
> +        return 0;
> +    }
> +}
> +
>  static inline void set_l2_entry(BDRVQcow2State *s, uint64_t *l2_slice,
>                                  int idx, uint64_t entry)
>  {
> +    idx *= l2_entry_size(s) / sizeof(uint64_t);
>      l2_slice[idx] = cpu_to_be64(entry);
>  }
>  
> +static inline void set_l2_bitmap(BDRVQcow2State *s, uint64_t *l2_slice,
> +                                 int idx, uint64_t bitmap)
> +{
> +    if (has_subclusters(s)) {
> +        idx *= l2_entry_size(s) / sizeof(uint64_t);
> +        l2_slice[idx + 1] = cpu_to_be64(bitmap);
> +    }
> +}
> +
>  static inline bool has_data_file(BlockDriverState *bs)
>  {
>      BDRVQcow2State *s = bs->opaque;
> 



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