Re: [Qemu-devel] [PATCH] proto: add 'shift' extension.

[Paolo Bonzini]

On 27/09/2016 15:28, Denis V. Lunev wrote:
> On 09/27/2016 03:07 PM, Paolo Bonzini wrote:
>>
>> ----- Original Message -----
>>> From: "Denis V. Lunev" <address@hidden>
>>> To: "Paolo Bonzini" <address@hidden>
>>> Cc: "Vladimir Sementsov-Ogievskiy" <address@hidden>, address@hidden, 
>>> address@hidden,
>>> address@hidden, address@hidden, address@hidden, address@hidden, 
>>> address@hidden,
>>> address@hidden
>>> Sent: Tuesday, September 27, 2016 12:25:54 PM
>>> Subject: Re: [PATCH] proto: add 'shift' extension.
>>>
>>> On 09/27/2016 01:15 PM, Paolo Bonzini wrote:
>>>>> We could go in a different direction and export flag
>>>>> 'has_zero_init' which will report that the storage is
>>>>> initialized with all zeroes at the moment. In this
>>>>> case mirroring code will not fall into this
>>>>> branch.
>>>> Why don't you add the zero_init flag to QEMU's NBD driver instead?
>>> for all cases without knowing real backend on the server side?
>>> I think this would be wrong.
>> Add it to the command line, and leave it to libvirt or the user to
>> pass "-drive file.driver=nbd,...,file.zero-init=on".
>
> I have started with something very similar for 'drive-mirror' command.
> We have added additional flag for this to improve migration speed
> and this was rejected.

You can add it through the filename path too, through a URI option
"nbd://...?zero-init=on".

Paolo