Re: [Qemu-devel] [PATCH] block: add drive_backup HMP command

[Paolo Bonzini]

Il 25/06/2013 16:06, Kevin Wolf ha scritto:
> Am 25.06.2013 um 15:49 hat Paolo Bonzini geschrieben:
>> Il 25/06/2013 15:26, Kevin Wolf ha scritto:
>>>>> +    if (!full) {
>>>>> +        error_setg(&errp, "-f is not yet implemented");
>>>>> +        hmp_handle_error(mon, &errp);
>>>>> +        return;
>>>>> +    }
>>> Then why make it a valid option and confuse users in the help text by
>>> describing options that don't really exist?
>>
>> Because otherwise we're stuck with a meaning of the flag that is
>> different between drive-mirror and block-backup.
> 
> Do you mean when "otherwise" isn't only "we don't add -f now", but also
> "we accidentally add a -f with different meaning later"? Not sure if
> there's a real danger of that when we're aware that we want -f with the
> same meaning as for mirroring.

We have drive-mirror with:
* the default is 'top'
* -f gives 'full'

block-backup for now only implements 'full'.  If we do not force the
user to add -f, the default is 'full' and we should not change it later.

However, I would move the "not yet implemented" error from HMP to QMP.
This way, both drive-mirror and block-backup will have a mandatory
'sync' argument.  We plan to implement it anyway, and it makes sense imo
to avoid gratuitous differences in the APIs.

Paolo

> Apart from that, it's HMP, so even in the unlikely case that we mess up,
> fixing it is still an option.
> 
> Kevin
>