Re: [Qemu-devel] [PATCH v2] file-posix: add drop-cache=on|off option

[Eric Blake]

On 3/6/19 4:18 AM, Stefan Hajnoczi wrote:

>> Question - if we used qapi's 'if':COND to only declare the field on
>> platforms where we know at compile time that we can support it, would
>> that be enough for libvirt to introspect that if the field exists then
>> migration is safe, without having to rely on an query-qemu-features command?
> 
> Yes, although this raises another question:
> 
> The drop-cache implementation is not #ifdefed in file-posix.c.  If we
> make the QMP schema conditional, should we also #ifdef the command-line
> option in raw_runtime_opts[] to prevent QEMU from silently ignoring this
> option?

Yes, that would make sense to me - if we don't advertise the feature,
then we should not silently ignore it on the command line.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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