Re: [Qemu-devel] [PATCH] doc: Allow NBD_CMD_FLAG_NO_HOLE during NBD_CMD_WRITE

[Denis V. Lunev]

On 04/04/2016 05:15 PM, Eric Blake wrote:
> qemu already has an existing server implementation option that will
> explicitly search the payload of NBD_CMD_WRITE for large blocks of
> zeroes, and punch holes in the underlying file.  For old clients
> that don't know how to use the new NBD_CMD_WRITE_ZEROES, this is a
> workaround to keep the server's destination file approximately as
> sparse as the client's source.  However, for new clients that know
> how to explicitly request holes, it is unnecessary overhead; and
> can lead to the server punching a hole and risking fragmentation or
> future ENOSPC even when the client explicitly wanted to write
> zeroes rather than a hole.  So it makes sense to let the new
> NBD_CMD_FLAG_NO_HOLE work for WRITE as well as WRITE_ZEROES.
>
> Signed-off-by: Eric Blake <address@hidden>

what behaviour do you expect  for QCOW2 file?
We should fully provision that image as far as I could understand,
i.e. allocate data blocks with zero content.

I think that this would work.