Re: [Qemu-devel] [PATCH v2 07/12] block/json: Add bdrv_co_get_block_status()

["Benoît Canet" <benoit.canet@irqsave.net>]

The Friday 07 Mar 2014 à 23:55:51 (+0100), Max Reitz wrote :
> Implement this function in the same way as raw_bsd does: Acknowledge
> that this is a passthrough driver (always return BDRV_BLOCK_OFFSET_VALID
> and BDRV_BLOCK_DATA and derive the offset directly from the sector
> index) and add BDRV_BLOCK_RAW to the returned value.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block/json.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/block/json.c b/block/json.c
> index e4cdb68..966a5f5 100644
> --- a/block/json.c
> +++ b/block/json.c
> @@ -110,6 +110,15 @@ static coroutine_fn int json_co_write_zeroes(BlockDriverState *bs,
>      return bdrv_co_write_zeroes(bs->file, sector_num, nb_sectors, flags);
>  }
>  
> +static coroutine_fn int64_t json_co_get_block_status(BlockDriverState *bs,
> +                                                     int64_t sector_num,
> +                                                     int nb_sectors, int *pnum)
> +{
> +    *pnum = nb_sectors;
> +    return BDRV_BLOCK_RAW | BDRV_BLOCK_OFFSET_VALID | BDRV_BLOCK_DATA |
> +           (sector_num << BDRV_SECTOR_BITS);
> +}
> +
>  static void json_invalidate_cache(BlockDriverState *bs)
>  {
>      return bdrv_invalidate_cache(bs->file);
> @@ -156,6 +165,7 @@ static BlockDriver bdrv_json = {
>      .bdrv_aio_discard           = json_aio_discard,
>  
>      .bdrv_co_write_zeroes       = json_co_write_zeroes,
> +    .bdrv_co_get_block_status   = json_co_get_block_status,
>  
>      .bdrv_invalidate_cache      = json_invalidate_cache,
>  
> -- 
> 1.9.0
> 

If this filter is stacked on top of qcow2 even the simple BDRV_BLOCK_RAW feel
weird.
I think the best thing we can do is to ask to Peter Lieven if this code has the
intended meaning in a block filter.

Peter: 

You wrote the inspiration for this code in raw-posix.c.

What do you think of this piece of code designed to be stacked as a block filter
on top of regular block driver (qcow2 etc) ?

Does it makes sense ? Or would it be better to forward the call to the lower
level ?

Best regards

Benoît