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

[Max Reitz <mreitz@redhat.com>]

On 28.05.2015 17:04, Max Reitz wrote:
> On 28.05.2015 17:02, Alberto Garcia wrote:
>> On Thu 28 May 2015 04:56:34 PM CEST, Max Reitz wrote:
>>>>          'compat': 'str',
>>>>          '*lazy-refcounts': 'bool',
>>>>          '*corrupt': 'bool',
>>>> -      'refcount-bits': 'int'
>>>> +      'refcount-bits': 'int',
>>>> +      'cache-clean-interval': 'int'
>>>>      } }
>>> I'm not too happy about making this part of ImageInfoSpecificQCow2.
>>> Two reasons for this: First, it's eventually part of ImageInfo, which
>>> is defined as "Information about a QEMU image file", but this option
>>> cannot be set in the image file itself but is only a run-time option.
>> That's a valid point. Now that I think of it, do we actually have a way
>> to retrieve the sizes of the L2 and refcount caches? I think cache-size,
>> l2-cache-size, and refcount-cache-size are already write-only values.
>
> No, in fact we don't. Well, except for if you manage to retrieve the 
> JSON filename for the qcow2 BDS, it should be part of that. :-P

And I just noticed, passing that option will result in qemu returning 
the JSON filename when queried:

$ qemu-img info "json:{'l2-cache-size':65536,'file.filename':'test.qcow2'}"
image: json:{"driver": "qcow2", "l2-cache-size": 65536, "file": 
{"driver": "file", "filename": "test.qcow2"}}
[…]

Max