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| From: | Eric Blake |
| Subject: | Re: [Qemu-devel] [PATCH 1/2] commit: Add top-node/base-node options |
| Date: | Wed, 5 Sep 2018 08:48:15 -0500 |
| User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 |
On 09/05/2018 07:38 AM, Peter Krempa wrote:
block-commit is able to reopen the format layers and works as expected.
Unfortunately though the 'read-only' option is actually useful as the
curl-driver does not work without it:
-blockdev
{"driver":"http","url":"http://ftp.sjtu.edu.cn:80/ubuntu-cd/12.04/ubuntu-12.04.5-alternate-amd64.iso","node-name":"libvirt-2-storage","discard":"unmap"}:
curl block device does not support writes
We obviously can encode that knowledge into libvirt but it will be hard
to undo if qemu eventually supports writes in the curl driver.
Which other protocol drivers don't support writes? in case we have to go
this way.
When an NBD server exported an image as read-only, the NBD block client cannot request write permissions. But that's a runtime discovery process, not a limitation of the block driver itself.
-- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
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