On 20.07.20 15:18, Kevin Wolf wrote: > qcow2 version 2 images don't support the zero flag for clusters, so for > write_zeroes requests, we return -ENOTSUP and get explicit zero buffer > writes. If the image doesn't have a backing file, we can do better: Just > discard the respective clusters. > > This is relevant for 'qemu-img convert -O qcow2 -n', where qemu-img has > to assume that the existing target image may contain any data, so it has > to write zeroes. Without this patch, this results in a fully allocated > target image, even if the source image was empty. > > Reported-by: Nir Soffer <[email protected]> > Signed-off-by: Kevin Wolf <[email protected]> > --- > block/qcow2-cluster.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-)
Reviewed-by: Max Reitz <[email protected]>
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