Re: [Qemu-devel] [PATCH 1/8] spec: add qcow2-dirty-bitmaps specification

[Eric Blake]

On 06/10/2015 02:19 AM, Vladimir Sementsov-Ogievskiy wrote:

>>> +Dirty bitmaps is an optional header extension. It provides a
>>> possibility of
>>> +storing dirty bitmaps in qcow2 image. The fields are:
>>> +
>>> +          0 -  3:  nb_dirty_bitmaps
>>> +                   Number of dirty bitmaps contained in the image
>> Is there a maximum?
> hmm. any proposals for this?
>>
>>> +
>>> +          4 - 11:  dirty_bitmaps_offset

I'm not sure if there is a reasonable cap on the number of dirty
bitmaps; I doubt that anyone will actually supply all 4G possible images
allowed by the four-byte field, but don't have a suggestion on a smaller
limit that doesn't feel arbitrary.

[meta-comment] It's very hard to pick out the new content in your reply
if you do not separate your new text with a newline both before and
after (as I'm doing here).


>>> +Dirty bitmaps are stored using a ONE-level structure for the mapping of
>>> +bitmaps to host clusters. There is only an L1 table.
>>> +
>>> +The L1 table has a variable size (stored in the Bitmap table entry)
>>> and may
>>> +use multiple clusters, however it must be contiguous in the image file.
>> The use of "L1 table" could be confusing.  The refcount metadata uses
>> "refcount table" and "refcount block" to describe a one-level table.
> I agree. Hmm.. dirty bitmaps table? ok?

"dirty bitmaps table" works for me, as a name for the one-level table.

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

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