Re: [PATCH 8/8] block: drop unallocated_blocks_are_zero

[Eric Blake]

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
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