Re: [Qemu-devel] [Qemu-block] [PATCH 5/7] qcow2: use byte-based read in qcow2_decompress_cluster

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

06.11.2018 16:53, Alberto Garcia wrote:
> On Thu 01 Nov 2018 07:27:36 PM CET, Vladimir Sementsov-Ogievskiy wrote:
>
>> diff --git a/block/qcow2.c b/block/qcow2.c
>> index e9d24b801e..950b9f7ec6 100644
>> --- a/block/qcow2.c
>> +++ b/block/qcow2.c
>> @@ -3956,14 +3956,15 @@ fail:
>>   int qcow2_decompress_cluster(BlockDriverState *bs, uint64_t cluster_offset)
>>   {
>>       BDRVQcow2State *s = bs->opaque;
>> -    int ret, csize, nb_csectors, sector_offset;
>> +    int ret, csize, nb_csectors;
>>       uint64_t coffset;
>> +    struct iovec iov;
>> +    QEMUIOVector local_qiov;
>>   
>>       coffset = cluster_offset & s->cluster_offset_mask;
>>       if (s->cluster_cache_offset != coffset) {
>>           nb_csectors = ((cluster_offset >> s->csize_shift) & s->csize_mask) + 1;
>> -        sector_offset = coffset & 511;
>> -        csize = nb_csectors * 512 - sector_offset;
>> +        csize = nb_csectors * 512 - (coffset & 511);
>>   
>>           /* Allocate buffers on first decompress operation, most images are
>>            * uncompressed and the memory overhead can be avoided.  The buffers
>> @@ -3981,14 +3982,17 @@ int qcow2_decompress_cluster(BlockDriverState *bs, uint64_t cluster_offset)
>>               s->cluster_cache = g_malloc(s->cluster_size);
>>           }
>>   
>> +        iov.iov_base = s->cluster_data;
>> +        iov.iov_len = csize;
>> +        qemu_iovec_init_external(&local_qiov, &iov, 1);
>> +
>>           BLKDBG_EVENT(bs->file, BLKDBG_READ_COMPRESSED);
>> -        ret = bdrv_read(bs->file, coffset >> 9, s->cluster_data,
>> -                        nb_csectors);
>> +        ret = bdrv_co_preadv(bs->file, coffset, csize, &local_qiov,
>> 0);
> I think you should annotate the function with coroutine_fn or use
> bdrv_pread() instead.
>
> Berto

it is called only from qcow2_co_preadv, so it's ok to move to 
already-in-coroutine behaviour. I'll add coroutine_fn if new version is 
needed, or it can be added inflight.

-- 
Best regards,
Vladimir