Re: [Qemu-block] [PATCH 1/4] block: add bdrv_get_format_alloc_stat format interface

[Eric Blake]

On 06/02/2017 10:26 AM, Vladimir Sementsov-Ogievskiy wrote:
> 30.05.2017 17:53, Eric Blake wrote:
>> On 05/30/2017 05:48 AM, Vladimir Sementsov-Ogievskiy wrote:
>>> The function should collect statistics, about allocted/unallocated by
>>> top-level format driver space (in its .file) and allocation status
>>> (allocated/hole/after eof) of corresponding areas in this .file.
>>>

>>> +# @BlockFormatAllocInfo:
>>> +#
>>> +# Information about allocations, including metadata. All fields are
>>> in bytes.
> 
> s/All fields are in bytes./All fields are in bytes and aligned by sector
> (512 bytes)./

I wouldn't even promise sector alignment. We probably happen to have
sector alignment (especially for qcow2, since the smallest cluster size
permitted is sector aligned), but I see no inherent reason why we can't
support sub-sector values if we are reporting in bytes.

> 
> - ok? to emphasize that there is nothing about clusters... Or may be
> better to write that they are aligned by byte.

I think "All fields are in bytes" is sufficient.


>>> +{ 'struct': 'BlockFormatAllocInfo',
>>> +  'data': {'alloc_alloc':    'uint64',
>>> +           'alloc_hole':     'uint64',
>>> +           'alloc_overhead': 'uint64',
>>> +           'hole_alloc':     'uint64',
>>> +           'hole_hole':      'uint64' } }
>> The idea seems okay, but the naming needs to be fixed.  Also, I'm not
>> sure if we need all 5, or if 4 is enough; and I'm not sure if we have
>> the right names ("how does alloc-hole differ from hole-alloc?"), or if
>> we can come up with something more descriptive.  Particularly since
>> "hole-" is not a hole in the filesystem sense, so much as unused
>> clusters.  But I'm also not coming up with better names to suggest at
>> the moment.
>>
> how about:
> 
> used-allocated
> used-discarded
> used-overrun
> 
> unused-allocated
> unused-discarded

Those work for me.

> 
> 
> also, do you mention that your detailed wordings should be included into
> block-core.json or you just clarify things?

Good documentation is worth the effort. I don't know if you want all of
my details in block-core.json, but giving a better overview of how each
statistic is possible does make it easier to visualize what the
statistic is actually counting.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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