On 10/17/18 11:41 AM, Kevin Wolf wrote:
If a management application builds the block graph node by node, the protocol layer doesn't inherit its read-only option from the format layer any more, so it must be set explicitly.
The documentation for this option is consciously phrased in a way that allows QEMU to switch to a better model eventually: Instead of trying when the image is first opened, making the read-only flag dynamic and changing it automatically whenever the first BLK_PERM_WRITE user is attached or the last one is detached would be much more useful behaviour.
+++ b/qapi/block-core.json @@ -3651,6 +3651,12 @@ # either generally or in certain configurations. In this case, # the default value does not work and the option must be # specified explicitly. +# @auto-read-only: if true and @read-only is false, QEMU may automatically +# decide not to open the image read-write as requested, but +# fall back to read-only instead (and switch between the modes +# later), e.g. depending on whether the image file is writable +# or whether a writing user is attached to the node +# (default: false, since 3.1)
Definitely better wording compared to v2. Reviewed-by: Eric Blake <ebl...@redhat.com> -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org