Re: [Qemu-devel] [PATCHv3 00/20] block: logical block provisioning enhancements

[Peter Lieven]

Am 07.10.2013 um 10:42 schrieb Stefan Hajnoczi <address@hidden>:

> On Tue, Sep 24, 2013 at 03:34:54PM +0200, Peter Lieven wrote:
>> this patch adds the ability for targets to stay sparse during
>> block migration (if the zero_blocks capability is set) and qemu-img convert
>> even if the target does not have has_zero_init = 1.
>> 
>> the series was especially developed for iSCSI, but it should also work
>> with other drivers with little or no adjustments. these adjustments
>> should be limited to providing block provisioning information through
>> get_block_info and/or honouring BDRV_REQ_MAY_UNMAP on writing zeroes.
> 
> Could you make bdrv_co_write_zeroes() always use UNMAP, if possible, and
> avoid adding the new BDRV_REQ_MAY_UNMAP flag?  While reading the first
> few patches in this series I wondered why there is a need to expose
> flags at all...
> 
> Sometimes it is useful to distinguish between zeroing at the image
> format level from discarding at the device level, but I don't think we
> make use of that yet.  I'd prefer to keep the interface simple for now
> and add flags later, if necessary.
> 
> Or maybe I just missed something ;)
> 

There was a big discussing going on on this flags some time ago with Paolo and 
Kevin and they wanted to have it.
(thread was "qemu-img: conditionally discard target on convert"). For my use 
case I don't need the flag.

Peter