Re: [Qemu-block] [PATCH 2/3] qcow2: add option to clean unused cache entries after some time

[Eric Blake]

On 05/28/2015 09:23 AM, Max Reitz wrote:

>>>> Can we mark the parameter optional, and only provide it when it is
>>>> non-zero?  That way, qemu-img (which cannot set an interval) will not
>>>> report it, and the only time it will appear is if it was set as part
>>>> of opening the block device under qemu.
>>> That sounds good.
>> But what do we do with the other parameters (refcount-cache-size,
>> l2-cache-size)? We cannot have the same solution there because they
>> don't belong to the image file either, and they're never going go be
>> zero.
> 
> Pssht, don't mention it, or Eric will notice. :-)
> 
> Well, one solution would be to remember whether they have been set
> explicitly or not. But that gets ugly really quickly. Maybe Kevin's
> series helps there, but I don't know.
> 
> Of course, the simplest solution is to worry about cache-clean-interval
> for now and worry about the cache sizes later… But that basically means
> "We'll never worry about them unless someone complains", so…

Hmm, now that we have three pieces of data, I'm starting to lean more
towards ImageInfoSpecific being the wrong place for this after all; it
would still be nice to advertise all three, but where?  Is
BlockdevCacheInfo more appropriate (as a sub-struct of BlockDeviceInfo)?

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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