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Re: [Qemu-block] [PATCH 4/5] block/qcow2-bitmap: Count queued bitmaps to
From: |
John Snow |
Subject: |
Re: [Qemu-block] [PATCH 4/5] block/qcow2-bitmap: Count queued bitmaps towards nb_bitmaps |
Date: |
Fri, 7 Jun 2019 14:24:26 -0400 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 |
On 6/7/19 10:58 AM, Vladimir Sementsov-Ogievskiy wrote:
> 06.06.2019 21:41, John Snow wrote:
>> When we check to see if we can store a bitmap, we don't check how many
>> we've queued up. This can cause a problem saving bitmaps on close
>> instead of when we request them to be added. With the stricter add
>> interface, prohibit these bitmaps specifically.
>>
>> To match, make the remove interface more strict as well; now rejecting
>> any requests to remove bitmaps that were never queued for storage.
>>
>> We don't need to "find" the bitmap when the interface has been given the
>> bitmap explicitly, but this is done to make sure that the bitmap given
>> actually does belong to the bs we were passed as a paranoia check to
>> enforce consistency.
>
> If you want to check it, I'd really prefer to do it explictly,
> by adding "bool bdrv_has_dirty_bitmap(bs, bitmap) handler, or bitmap.bs
> field",
> instead of hiding it under inconvenient interface of helper, so we actually do
>
> name = bdrv_dirty_bitmap_name(bitmap);
> bitmap = bdrv_find_dirty_bitmap(bs, name);
>
> it really looks strange.
>
You're right, it does look weird. It's not obvious when you read it what
the real purpose is. I'll try to rectify it with an explicit helper like
you suggest.
> Hmmm, when I read series cover letter and this commit message, I thought
> that you'll just calculate current number of persistent bitmaps on bs..
> Do we really need to introduce additional counters on qcow2 state?
>
I suppose I could do that, too -- that seems a bit heavier than just
incrementing a counter, but it has less risk of getting out of sync.
> So, you want to check nb_queued + s->nb_bitmaps instead of just s->nb_bitmaps.
>
> I think we can just count persistent dirty bitmaps and take that number
> (as, there should not be in-image bitmaps, for which we don't have in-ram
> version, but we can check it too and return an error on mismatch (or count
> in-image-not-in-ram bitmaps and this count to number of in-ram persistent
> bitmaps it seems an extra thing)..
>
If I cache the bm_list as discussed in patch 2, we can actually avoid
re-enumerating all of the bitmaps and just go off of that data without
having to add any new counters.
--js
- Re: [Qemu-block] [PATCH 2/5] block/dirty-bitmap: Refactor bdrv_can_store_new_bitmap, (continued)
- Re: [Qemu-block] [PATCH 2/5] block/dirty-bitmap: Refactor bdrv_can_store_new_bitmap, John Snow, 2019/06/07
- Re: [Qemu-block] [PATCH 2/5] block/dirty-bitmap: Refactor bdrv_can_store_new_bitmap, Eric Blake, 2019/06/07
- Re: [Qemu-block] [PATCH 2/5] block/dirty-bitmap: Refactor bdrv_can_store_new_bitmap, Vladimir Sementsov-Ogievskiy, 2019/06/07
- Re: [Qemu-block] [PATCH 2/5] block/dirty-bitmap: Refactor bdrv_can_store_new_bitmap, Vladimir Sementsov-Ogievskiy, 2019/06/07
- Re: [Qemu-block] [PATCH 2/5] block/dirty-bitmap: Refactor bdrv_can_store_new_bitmap, John Snow, 2019/06/07
- Re: [Qemu-block] [PATCH 2/5] block/dirty-bitmap: Refactor bdrv_can_store_new_bitmap, Vladimir Sementsov-Ogievskiy, 2019/06/10
[Qemu-block] [PATCH 4/5] block/qcow2-bitmap: Count queued bitmaps towards nb_bitmaps, John Snow, 2019/06/06
[Qemu-block] [PATCH 5/5] block/qcow2-bitmap: Count queued bitmaps towards directory_size, John Snow, 2019/06/06
Re: [Qemu-block] [Qemu-devel] [PATCH 0/5] block/dirty-bitmap: check number and size constraints against queued bitmaps, no-reply, 2019/06/06