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

[Paolo Bonzini <pbonzini@redhat.com>]

Il 19/07/2013 08:48, Peter Lieven ha scritto:
>> @@ -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?

Perhaps bdrv_has_zero_init(bs) could be replaced by bs->backing_hd.  I'd
have to look at the code more closely.

But I suggest that you try using get_block_status (the function in
qemu-img.c) instead of bdrv_is_allocated in qemu-img.c.  It will
probably simplify your code _and_ make it more efficient.

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

Paolo