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util/hbitmap: strict hbitmap_reset

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hbitmap_reset has an unobvious property: it rounds requested region up.
It may provoke bugs, like in recently fixed write-blocking mode of
mirror: user calls reset on unaligned region, not keeping in mind that
there are possible unrelated dirty bytes, covered by rounded-up region
and information of this unrelated "dirtiness" will be lost.

Make hbitmap_reset strict: assert that arguments are aligned, allowing
only one exception when @start + @count == hb->orig_size. It's needed
to comfort users of hbitmap_next_dirty_area, which cares about
hb->orig_size.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20190806152611.280389-1-vsementsov@virtuozzo.com>
[Maintainer edit: Max's suggestions from on-list. --js]
[Maintainer edit: Eric's suggestion for aligned macro. --js]
Signed-off-by: John Snow <jsnow@redhat.com>
This commit is contained in:
Vladimir Sementsov-Ogievskiy 2019-08-06 18:26:11 +03:00 committed by John Snow
parent f22f553eff
commit 48557b1383
3 changed files with 10 additions and 1 deletions
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5
include/qemu/hbitmap.h
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@ -132,6 +132,11 @@ void hbitmap_set(HBitmap *hb, uint64_t start, uint64_t count);
* @count: Number of bits to reset.
*
* Reset a consecutive range of bits in an HBitmap.
* @start and @count must be aligned to bitmap granularity. The only exception
* is resetting the tail of the bitmap: @count may be equal to hb->orig_size -
* @start, in this case @count may be not aligned. The sum of @start + @count is
* allowed to be greater than hb->orig_size, but only if @start < hb->orig_size
* and @start + @count = ALIGN_UP(hb->orig_size, granularity).
*/
void hbitmap_reset(HBitmap *hb, uint64_t start, uint64_t count);

2
tests/test-hbitmap.c
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@ -423,7 +423,7 @@ static void test_hbitmap_granularity(TestHBitmapData *data,
hbitmap_test_check(data, 0);
hbitmap_test_set(data, 0, 3);
g_assert_cmpint(hbitmap_count(data->hb), ==, 4);
hbitmap_test_reset(data, 0, 1);
hbitmap_test_reset(data, 0, 2);
g_assert_cmpint(hbitmap_count(data->hb), ==, 2);
}

4
util/hbitmap.c
View File

@ -476,6 +476,10 @@ void hbitmap_reset(HBitmap *hb, uint64_t start, uint64_t count)
/* Compute range in the last layer. */
uint64_t first;
uint64_t last = start + count - 1;
uint64_t gran = 1ULL << hb->granularity;
assert(QEMU_IS_ALIGNED(start, gran));
assert(QEMU_IS_ALIGNED(count, gran) || (start + count == hb->orig_size));
trace_hbitmap_reset(hb, start, count,
start >> hb->granularity, last >> hb->granularity);