Re: [Qemu-block] [Qemu-devel] [PATCH 2/2] Add file-posix-dynamic-auto-read-only feature

[Peter Krempa]

On Fri, Mar 29, 2019 at 08:52:13 +0100, Kevin Wolf wrote:
> Am 28.03.2019 um 19:45 hat Eric Blake geschrieben:
> > On 3/28/19 1:28 PM, Kevin Wolf wrote:
> > > auto-read-only=on changed its behaviour in file-posix for the 4.0
> > > release. This change cannot be detected through the usual mechanisms
> > > like schema introspection. Add a new feature to query-qemu-features to
> > > allow libvirt to detect the presence of the new behaviour.
> > 
> > Oddly enough, introspecting the schema is sufficient to learn about this
> > particular feature (that is, until we actually have a runtime feature
> > that requires us to run the command, merely seeing what features the
> > command supports is useful on its own). But that doesn't change the fact
> > that we should keep things as a command.
> 
> Yes, I thought the same. But without the command, the type would
> disapear from query-qmp-schema, so it has to be there either way.
> 
> I think, however, that libvirt should actually run the command, not only
> test for its presence. Maybe we end up with some case where a new
> version can't provide the feature unconditionally for some reason, and
> then we want to be able to turn a static feature into a runtime one.

I'm definitely going to call the command. Actually I'm working on
implementing it right now. One benefit of doing it right away is that we
don't have any capability test data for the new version yet, so they
will not have to be updated once we'd actually need to call the command.

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