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Re: [Qemu-block] [Qemu-devel] [PATCH v5 05/18] dirty-bitmap: Change bdrv

From: John Snow
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH v5 05/18] dirty-bitmap: Change bdrv_dirty_bitmap_size() to report bytes
Date: Thu, 13 Jul 2017 13:37:44 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1

On 07/12/2017 09:05 PM, 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.  A later cleanup will
> convert dirty bitmap internals to be entirely byte-based,
> eliminating the intermediate sector rounding added here; and
> technically, since bdrv_getlength() already rounds up to sectors,
> our use of DIV_ROUND_UP is more for theoretical completeness than
> for any actual rounding.
> 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, and
> add an assertion where bdrv_getlength() should not fail.
> Signed-off-by: Eric Blake <address@hidden>

Reviewed-by: John Snow <address@hidden>

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