Am 01.07.2013 um 16:13 schrieb Stefan Hajnoczi <stefa...@redhat.com>:
> On Thu, Jun 27, 2013 at 03:11:32PM +0200, Peter Lieven wrote:
>
> This patch breaks cross-version blog migration. We need to control
> whether or not to use the new BLK_MIG_FLAG_ZERO_BLOCK flag.
you are right the upgrade way works, but downgrade not. what is the
proposed way to fix this?
>
>> diff --git a/block-migration.c b/block-migration.c
>> index 2fd7699..99b3757 100644
>> --- a/block-migration.c
>> +++ b/block-migration.c
>> @@ -29,6 +29,7 @@
>> #define BLK_MIG_FLAG_DEVICE_BLOCK 0x01
>> #define BLK_MIG_FLAG_EOS 0x02
>> #define BLK_MIG_FLAG_PROGRESS 0x04
>> +#define BLK_MIG_FLAG_ZERO_BLOCK 0x08
>>
>> #define MAX_IS_ALLOCATED_SEARCH 65536
>>
>> @@ -114,16 +115,29 @@ static void blk_mig_unlock(void)
>> static void blk_send(QEMUFile *f, BlkMigBlock * blk)
>> {
>> int len;
>> + int flags = BLK_MIG_FLAG_DEVICE_BLOCK;
>> +
>> + if (buffer_is_zero(blk->buf, BLOCK_SIZE)) {
>> + flags |= BLK_MIG_FLAG_ZERO_BLOCK;
>> + }
>>
>> /* sector number and flags */
>> qemu_put_be64(f, (blk->sector << BDRV_SECTOR_BITS)
>> - | BLK_MIG_FLAG_DEVICE_BLOCK);
>> + | flags);
>
> blk->sector is int64_t and flags is signed int. This conversion will
> sign-extend from 32-bit flags up to 64-bits.
>
> Flags should be uint64_t or at least unsigned so that we don't hit
> sign-extension when BLK_MIG_FLAG_x uses the top bit.
will fix this. thanks,
Peter
