Re: [Qemu-devel] [PATCH 2/2] migration/block: use blk_pwrite_zeroes for each zero cluster

[858585 jemmy]

On Fri, Apr 7, 2017 at 3:08 PM, Fam Zheng <address@hidden> wrote:
> On Thu, 04/06 21:15, address@hidden wrote:
>> From: Lidong Chen <address@hidden>
>>
>> BLOCK_SIZE is (1 << 20), qcow2 cluster size is 65536 by default,
>> this maybe cause the qcow2 file size is bigger after migration.
>> This patch check each cluster, use blk_pwrite_zeroes for each
>> zero cluster.
>>
>> Signed-off-by: Lidong Chen <address@hidden>
>> ---
>>  migration/block.c | 34 ++++++++++++++++++++++++++++++++--
>>  1 file changed, 32 insertions(+), 2 deletions(-)
>>
>> diff --git a/migration/block.c b/migration/block.c
>> index 7734ff7..1fce9b9 100644
>> --- a/migration/block.c
>> +++ b/migration/block.c
>> @@ -885,6 +885,10 @@ static int block_load(QEMUFile *f, void *opaque, int 
>> version_id)
>>      int64_t total_sectors = 0;
>>      int nr_sectors;
>>      int ret;
>> +    int i;
>> +    int cluster_size;
>> +    int64_t addr_offset;
>> +    uint8_t *buf_offset;
>>
>>      do {
>>          addr = qemu_get_be64(f);
>> @@ -934,8 +938,34 @@ static int block_load(QEMUFile *f, void *opaque, int 
>> version_id)
>>              } else {
>>                  buf = g_malloc(BLOCK_SIZE);
>>                  qemu_get_buffer(f, buf, BLOCK_SIZE);
>> -                ret = blk_pwrite(blk, addr * BDRV_SECTOR_SIZE, buf,
>> -                                 nr_sectors * BDRV_SECTOR_SIZE, 0);
>> +
>> +                cluster_size = bdrv_get_cluster_size(blk_bs(blk));
>> +
>> +                if (cluster_size > 0) {
>> +                    for (i = 0; i < BLOCK_SIZE / cluster_size; i++) {
>
> Should we check that cluster_size < BLOCK_SIZE and (BLOCK_SIZE % cluster_size 
> ==
> 0)?
I think this is necessary.
Thanks.

>
> Fam
>
>> +                        addr_offset = addr * BDRV_SECTOR_SIZE
>> +                                        + i * cluster_size;
>> +                        buf_offset = buf + i * cluster_size;
>> +
>> +                        if (buffer_is_zero(buf_offset, cluster_size)) {
>> +                            ret = blk_pwrite_zeroes(blk, addr_offset,
>> +                                                    cluster_size,
>> +                                                    BDRV_REQ_MAY_UNMAP);
>> +                        } else {
>> +                            ret = blk_pwrite(blk, addr_offset,
>> +                                             buf_offset, cluster_size, 0);
>> +                        }
>> +
>> +                        if (ret < 0) {
>> +                            g_free(buf);
>> +                            return ret;
>> +                        }
>> +                    }
>> +                } else {
>> +                    ret = blk_pwrite(blk, addr * BDRV_SECTOR_SIZE, buf,
>> +                                     nr_sectors * BDRV_SECTOR_SIZE, 0);
>> +                }
>> +
>>                  g_free(buf);
>>              }
>>
>> --
>> 1.8.3.1
>>