Re: [PATCH] block: use the request length for iov alignment

[Damien Le Moal]

On 2022/09/13 15:12, Keith Busch wrote:
> On Thu, Sep 08, 2022 at 09:45:26AM -0700, Keith Busch wrote:
>> From: Keith Busch <kbusch@kernel.org>
>>
>> An iov length needs to be aligned to the logical block size, which may
>> be larger than the memory alignment.
> 
> [cc'ing some other interested folks]
> 
> Any thoughts on this patch? It is fixing an observed IO error  when running
> virtio-blk with the default 512b logical block size backed by a drive 
> formatted
> with 4k logical block.

The patch look OK to me, but having virtio expose a 512B LBA size for a backing
device that has 4K LBAs will break all IOs if caching is turned off (direct IOs
case), even if this patch is applied. No ?

> 
>> ---
>>  block/io.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/block/io.c b/block/io.c
>> index 0a8cbefe86..296d4b49a7 100644
>> --- a/block/io.c
>> +++ b/block/io.c
>> @@ -3243,13 +3243,14 @@ bool bdrv_qiov_is_aligned(BlockDriverState *bs, 
>> QEMUIOVector *qiov)
>>  {
>>      int i;
>>      size_t alignment = bdrv_min_mem_align(bs);
>> +    size_t len = bs->bl.request_alignment;
>>      IO_CODE();
>>  
>>      for (i = 0; i < qiov->niov; i++) {
>>          if ((uintptr_t) qiov->iov[i].iov_base % alignment) {
>>              return false;
>>          }
>> -        if (qiov->iov[i].iov_len % alignment) {
>> +        if (qiov->iov[i].iov_len % len) {
>>              return false;
>>          }
>>      }
>> -- 
>> 2.30.2
>>

-- 
Damien Le Moal
Western Digital Research