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

[Stefan Hajnoczi]

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 ;)

Stefan