Re: [Qemu-devel] [PATCH v2 10/17] block: define get_block_status return value

[Peter Lieven]

On 16.07.2013 18:29, Paolo Bonzini wrote:
> Define the return value of get_block_status.  Bits 0, 1, 2 and 9-62
> are valid; bit 63 (the sign bit) is reserved for errors.  Bits 3-7
> are left for future extensions.
>
> The return code is compatible with the old is_allocated API: returning
> just 0 or 1 (aka BDRV_BLOCK_DATA) will not cause any behavioral change
> in clients of is_allocated.  We will return more precise information
> in the next patches.
>
> Signed-off-by: Paolo Bonzini <address@hidden>
> ---
>          v1->v2: improved comment
>
>   block.c               |  7 +++++--
>   include/block/block.h | 26 ++++++++++++++++++++++++++
>   2 files changed, 31 insertions(+), 2 deletions(-)
>
> diff --git a/block.c b/block.c
> index 6e7a8a3..7ff0716 100644
> --- a/block.c
> +++ b/block.c
> @@ -2990,7 +2990,7 @@ static int64_t coroutine_fn 
> bdrv_co_get_block_status(BlockDriverState *bs,
>   
>       if (!bs->drv->bdrv_co_get_block_status) {
>           *pnum = nb_sectors;
> -        return 1;
> +        return BDRV_BLOCK_DATA;
>       }
>   
>       return bs->drv->bdrv_co_get_block_status(bs, sector_num, nb_sectors, pnum);
> @@ -3040,7 +3040,10 @@ int64_t bdrv_get_block_status(BlockDriverState *bs, 
> int64_t sector_num,
>   int coroutine_fn bdrv_is_allocated(BlockDriverState *bs, int64_t sector_num,
>                                      int nb_sectors, int *pnum)
>   {
> -    return bdrv_get_block_status(bs, sector_num, nb_sectors, pnum);
> +    int64_t ret = bdrv_get_block_status(bs, sector_num, nb_sectors, pnum);
> +    return
> +        (ret & BDRV_BLOCK_DATA) ||
> +        ((ret & BDRV_BLOCK_ZERO) && !bdrv_has_zero_init(bs));

i do also not understand the "((ret & BDRV_BLOCK_ZERO) && 
!bdrv_has_zero_init(bs))";
if a block is unallocated and reads as zero, but the device lacks zero init, it
is declared as allocated with this, isn't it?

for iscsi and host_device with lbprz==1 or discardzeroes respectively all
blocks would return as allocated. is this wanted?

Peter