Re: [PATCH 3/3] qcow2: Use BDRV_SECTOR_SIZE instead of the hardcoded value

[Alberto Garcia]

On Thu 09 Jan 2020 01:19:00 PM CET, Kevin Wolf wrote:
>> diff --git a/block/qcow2.c b/block/qcow2.c
>> index e8ce966f7f..6427c75409 100644
>> --- a/block/qcow2.c
>> +++ b/block/qcow2.c
>> @@ -2175,7 +2175,7 @@ static coroutine_fn int 
>> qcow2_co_preadv_task(BlockDriverState *bs,
>>                                            offset, bytes, qiov, qiov_offset);
>>  
>>      case QCOW2_CLUSTER_NORMAL:
>> -        if ((file_cluster_offset & 511) != 0) {
>> +        if ((file_cluster_offset % BDRV_SECTOR_SIZE) != 0) {
>>              return -EIO;
>>          }
>
> Hm, unrelated to your change, but why do we test for 512 byte
> alignment here? file_cluster_offset should certainly be cluster
> aligned for normal clusters. And if the check fails, that's actually
> an image corruption and not just an I/O error. Am I missing something?

I actually suspect that this is just an old, obsolete check that we have
kept during these years. file_cluster_offset should be not just sector
aligned but also cluster aligned if I'm not wrong, and if not then
qcow2_alloc_cluster_offset() and qcow2_get_cluster_offset() should
return an error.

I can simply remove that check, or replace it with an assertion.

Berto