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From: | Eric Blake |
Subject: | Re: [PATCH 8/8] block: drop unallocated_blocks_are_zero |
Date: | Wed, 6 May 2020 10:50:40 -0500 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 |
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
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