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Re: [Qemu-block] [Qemu-devel] [PATCH v4 05/17] dirty-bitmap: Change bdrv

From: Eric Blake
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH v4 05/17] dirty-bitmap: Change bdrv_dirty_bitmap_size() to report bytes
Date: Mon, 10 Jul 2017 16:19:47 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1

On 07/10/2017 04:09 PM, John Snow wrote:
> On 07/03/2017 11:10 AM, Eric Blake wrote:
>> We are still using an internal hbitmap that tracks a size in sectors,
>> with the granularity scaled down accordingly, because it lets us
>> use a shortcut for our iterators which are currently sector-based.
>> But there's no reason we can't track the dirty bitmap size in bytes,
>> since it is (mostly) an internal-only variable (remember, the size
>> is how many bytes are covered by the bitmap, not how many bytes the
>> bitmap occupies).  Furthermore, we're already reporting bytes for
>> bdrv_dirty_bitmap_granularity(); mixing bytes and sectors in our
>> return values is a recipe for confusion.
>> The only external caller in qcow2-bitmap.c is temporarily more verbose
>> (because it is still using sector-based math), but will later be
>> switched to track progress by bytes instead of sectors.
>> Use is_power_of_2() while at it, instead of open-coding that.
>> Signed-off-by: Eric Blake <address@hidden>

>> @@ -305,8 +307,10 @@ BdrvDirtyBitmap
>> *bdrv_reclaim_dirty_bitmap(BlockDriverState *bs,
>>   void bdrv_dirty_bitmap_truncate(BlockDriverState *bs)
>>   {
>>       BdrvDirtyBitmap *bitmap;
>> -    uint64_t size = bdrv_nb_sectors(bs);
>> +    int64_t size = bdrv_getlength(bs);
>> +    assert(size >= 0);
>> +    size = DIV_ROUND_UP(size, BDRV_SECTOR_SIZE);
> Do we need a TODO here as well, or are we going to track these in terms
> of "sectors" permanently?

The rounding goes away in patch 17/17 when I flip the internals to
byte-based.  If a TODO comment here (that goes away in patch 17) makes
review easier, I can add that.

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

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