Re: [Qemu-devel] [PATCH v3 18/22] qcow2: Use intermediate helper CB for amend

[Max Reitz <mreitz@redhat.com>]

On 2014-11-28 at 15:13, Stefan Hajnoczi wrote:
> On Thu, Nov 20, 2014 at 06:06:34PM +0100, Max Reitz wrote:
>> @@ -2674,6 +2743,7 @@ static int qcow2_amend_options(BlockDriverState *bs, QemuOpts *opts,
>>       bool encrypt;
>>       int ret;
>>       QemuOptDesc *desc = opts->list->desc;
>> +    Qcow2AmendHelperCBInfo helper_cb_info;
>>   
>>       while (desc && desc->name) {
>>           if (!qemu_opt_find(opts, desc->name)) {
>> @@ -2731,6 +2801,12 @@ static int qcow2_amend_options(BlockDriverState *bs, QemuOpts *opts,
>>           desc++;
>>       }
>>   
>> +    helper_cb_info = (Qcow2AmendHelperCBInfo){
>> +        .original_status_cb = status_cb,
>> +        .original_cb_opaque = cb_opaque,
>> +        .total_operations = (new_version < old_version)
> If you respin, another way of writing this is without total_operations
> here (so it initializes to 0)...
>
>> +    };
>> +
>>       /* Upgrade first (some features may require compat=1.1) */
>>       if (new_version > old_version) {
>>           s->qcow_version = new_version;
>> @@ -2789,7 +2865,9 @@ static int qcow2_amend_options(BlockDriverState *bs, QemuOpts *opts,
>>   
>>       /* Downgrade last (so unsupported features can be removed before) */
>>       if (new_version < old_version) {
>> -        ret = qcow2_downgrade(bs, new_version, status_cb, cb_opaque);
>> +        helper_cb_info.current_operation = QCOW2_DOWNGRADING;
> ...and then helper_cb_info.total_operations++ here.
>
> That way the new_version < old_version check is not duplicated into the
> helper_cb_info initializer.
>
> The code is clearer because we assign current_operation and
> total_operations at the same time.
>
> Just a style suggestion, feel free to ignore if you don't like it.

I think helper_cb_info.total_operations should be set right when 
creating the object. We can only do .total_operations++ once, and that 
is for the very first operation because after that is executed, we may 
no longer change .total_operations; and I don't think we should treat 
the first operation differently than the rest.

Max