Re: [bugfix ping2] Re: [PATCH v2 0/2] fix qcow2_can_store_new_dirty_bitmap

[Eric Blake <eblake@redhat.com>]

On 12/9/19 11:58 AM, Max Reitz wrote:
> On 09.12.19 17:30, Max Reitz wrote:
>> On 02.12.19 15:09, Vladimir Sementsov-Ogievskiy wrote:
>>> Hi again!
>>>
>>> Still forgotten bug-fix :(
>>>
>>> Is it too late for 4.2?
>>
>> Sorry. :-/
>>
>> Yes, I think I just forgot it.  I don’t think it’s too important for
>> 4.2, so, well, it isn’t too bad, but...  Sorry.
>>
>>> I can't imagine better test, and it tests exactly what written in
>>> https://bugzilla.redhat.com/show_bug.cgi?id=1712636
>>>
>>> (Hmm, actually, I doubt that it is real use-case, more probably it's a bug in management layer)
>>>
>>> So, take this with test or without test, to 4.2 or 5.0.
>>
>> I was thinking of seeing whether I could write a quicker test, but of
>> course we should take the patch either way.
> 
> OK, I give up.  It’s very much possible to create an image with 65535
> bitmaps very quickly (like, under a second) outside of qemu, but just
> opening it takes 2:30 min (because of the quadratic complexity of
> checking whether a bitmap of the same name already exists).

Can we fix that to use a hash table for amortized O(1) lookup rather 
than the current O(n) lookup?

But such a fix is 5.0 material.

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