Re: [Qemu-devel] [PATCH v3 1/2] block: sync bdrv_co_get_block_status_above() with bdrv_is_allocated_above()

[Denis V. Lunev]

On 09/19/2016 04:21 AM, Fam Zheng wrote:
> On Thu, 09/15 19:34, Denis V. Lunev wrote:
>> They should work very similar, covering same areas if backing store is
>> shorter than the image. This change is necessary for the followup patch
>> switching to bdrv_get_block_status_above() in mirror to avoid assert
>> in check_block.
>>
>> This change should be made very carefully. Let us assume that we have
>> top image and 2 backing stores L0->L1->L2.
> Stupid question: which one is top and which are backing?
L0 is top, L2 is at bottom.


>>   L0: --------------
>>   L1: -------
>>   L2: -------=======
>> The data marked as '=' in L2 should not appear as BDRV_BLOCK_ALLOCATED
>> and we should return it as filled in L0 image with properly calculated
>> *pnum value.
> What '-', '=' and ' ' represent aren't immediately clear to me, could you put 
> a
> legend in the message too? Something like:
>
>     '-': allocated
>     '=': unallocated
>     ' ': beyong EOF
ok.

here '-' in unallocated
'=' is allocated.
virtual size of L1 image is shorter that L2 and L0, thus ' ' is beyond EOF.

Thank you, will rewrite today.

Den
>> Signed-off-by: Denis V. Lunev <address@hidden>
>> CC: Stefan Hajnoczi <address@hidden>
>> CC: Fam Zheng <address@hidden>
>> CC: Kevin Wolf <address@hidden>
>> CC: Max Reitz <address@hidden>
>> CC: Jeff Cody <address@hidden>
>> ---
>>  block/io.c | 25 ++++++++++++++++++++-----
>>  1 file changed, 20 insertions(+), 5 deletions(-)
>>
>> diff --git a/block/io.c b/block/io.c
>> index 420944d..067d465 100644
>> --- a/block/io.c
>> +++ b/block/io.c
>> @@ -1741,18 +1741,33 @@ static int64_t coroutine_fn 
>> bdrv_co_get_block_status_above(BlockDriverState *bs,
>>          BlockDriverState **file)
>>  {
>>      BlockDriverState *p;
>> -    int64_t ret = 0;
>> +    int64_t ret = 0, res = nb_sectors;
>>  
>>      assert(bs != base);
>>      for (p = bs; p != base; p = backing_bs(p)) {
>> -        ret = bdrv_co_get_block_status(p, sector_num, nb_sectors, pnum, 
>> file);
>> -        if (ret < 0 || ret & BDRV_BLOCK_ALLOCATED) {
>> -            break;
>> +        int sc;
>> +        ret = bdrv_co_get_block_status(p, sector_num, nb_sectors, &sc, 
>> file);
>> +        if (ret < 0) {
>> +            return ret;
>> +        } else if (ret & BDRV_BLOCK_ALLOCATED) {
>> +            *pnum = sc;
>> +            return ret;
>> +        }
>> +
>> +        if (res > sc && (p == bs || sector_num + sc < p->total_sectors)) {
>> +            res = sc;
>>          }
>> +
>>          /* [sector_num, pnum] unallocated on this layer, which could be only
>>           * the first part of [sector_num, nb_sectors].  */
>> -        nb_sectors = MIN(nb_sectors, *pnum);
>> +        nb_sectors = MIN(nb_sectors, sc);
>> +
>> +        if (nb_sectors == 0) {
>> +            break;
>> +        }
>>      }
>> +
>> +    *pnum = res;
>>      return ret;
>>  }
>>  
>> -- 
>> 2.7.4
>>
>>