On 5/6/20 4:25 AM, Vladimir Sementsov-Ogievskiy wrote:
Currently this field only set by qed and qcow2. But in fact, all backing-supporting formats (parallels, qcow, qcow2, qed, vmdk) share this semantics: on unallocated blocks, if there is no backing file they just memset the buffer with zeroes.
In checking the behavior of all 5 .supports_backing drivers, I noticed that qed.c:qed_read_backing_file() does a lot of redundant work in computing the backing file size itself, when it could just defer to the block layer like all the other drivers do. That would be a separate patch.
-- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
