Re: [Qemu-devel] [PATCH v3 12/19] block: return get_block_status data and flags for formats

[Paolo Bonzini <pbonzini@redhat.com>]

Il 30/07/2013 16:40, Kevin Wolf ha scritto:
> Am 25.07.2013 um 16:23 hat Paolo Bonzini geschrieben:
>> Reviewed-by: Eric Blake <eblake@redhat.com>
>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>> ---
>>  block/cow.c      |  8 +++++++-
>>  block/qcow.c     |  9 ++++++++-
>>  block/qcow2.c    | 16 ++++++++++++++--
>>  block/qed.c      | 35 ++++++++++++++++++++++++++++-------
>>  block/sheepdog.c |  2 +-
>>  block/vdi.c      | 13 ++++++++++++-
>>  block/vmdk.c     | 19 ++++++++++++++++++-
>>  block/vvfat.c    | 11 ++++++-----
>>  8 files changed, 94 insertions(+), 19 deletions(-)
>>
>> diff --git a/block/cow.c b/block/cow.c
>> index e738b96..1e90413 100644
>> --- a/block/cow.c
>> +++ b/block/cow.c
>> @@ -194,7 +194,13 @@ static int coroutine_fn cow_co_is_allocated(BlockDriverState *bs,
>>  static int64_t coroutine_fn cow_co_get_block_status(BlockDriverState *bs,
>>          int64_t sector_num, int nb_sectors, int *num_same)
>>  {
>> -    return cow_co_is_allocated(bs, sector_num, nb_sectors, num_same);
>> +    BDRVCowState *s = bs->opaque;
>> +    int ret = cow_co_is_allocated(bs, sector_num, nb_sectors, num_same);
>> +    int64_t offset = s->cow_sectors_offset + (sector_num << BDRV_SECTOR_BITS);
>> +    if (ret < 0) {
>> +        return ret;
>> +    }
>> +    return (ret ? BDRV_BLOCK_DATA : 0) | offset | BDRV_BLOCK_OFFSET_VALID;
>>  }
>>  
>>  static int cow_update_bitmap(BlockDriverState *bs, int64_t sector_num,
>> diff --git a/block/qcow.c b/block/qcow.c
>> index acd1aeb..1a65822 100644
>> --- a/block/qcow.c
>> +++ b/block/qcow.c
>> @@ -410,7 +410,14 @@ static int64_t coroutine_fn qcow_co_get_block_status(BlockDriverState *bs,
>>      if (n > nb_sectors)
>>          n = nb_sectors;
>>      *pnum = n;
>> -    return (cluster_offset != 0);
>> +    if (!cluster_offset) {
>> +        return 0;
> 
> If you take your comment in patch 11 serious, you should return
> bs->backing_hd ? 0 : BDRV_BLOCK_ZERO instead. (I think it would be
> useful behaviour, too, because knowing that a sector is zero enables
> optimisations in several places.)
> 
> Of course, this is something that could be done in the block.c
> implementation of bdrv_co_get_block_status() instead of each single
> driver.

And it is, in patch 15 ("block: use bdrv_has_zero_init to return
BDRV_BLOCK_ZERO"). :)  Should I reorder the patches?

Paolo