Am 11.05.2018 um 17:36 hat Ivan Ren geschrieben: > Create a qcow2 directly on bare block device with > "-o preallocation=metadata" option. When read this qcow2, it will > return pre-existing data on block device. This patch add > QCOW_OFLAG_ZERO flag (supported in qcow_version >= 3) for > preallocated l2 entry to avoid this problem. > > Signed-off-by: Ivan Ren <ivan...@tencent.com>
Doesn't this defeat the purpose of preallocation? Usually, the idea with preallocation is that you don't need to update any metadata on the first write, but if you set QCOW_OFLAG_ZERO, we do need a metadata update again. So what's the advantage compared to not preallocating at all? Kevin
