Re: Bug? qemu-img convert to preallocated image makes it sparse

["Richard W.M. Jones" <rjones@redhat.com>]

On Thu, Jan 16, 2020 at 05:38:03PM +0200, Maxim Levitsky wrote:
> How about doing write zeros without discard only in this particular case (convert to existing image)
> Basically omitting the BDRV_REQ_MAY_UNMAP flag to blk_co_pwrite_zeroes.
> It will be slow, but maybe for this particular case, it is acceptable?

I should probably say that we don't want to break the other case
(which is likely more important) where we write a sparse source to a
sparse target and want the target to contain only the union of the two
sparse maps, not fully allocated :-)

It would be fine, I think, to have a new "make this disk fully
allocated" operation.  qemu-img resize could almost do it with a
request to add 0 extra bytes, but the --preallocation flag only
applies to the new space.

Rich.

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