Commit 48557b13 authored by Vladimir Sementsov-Ogievskiy's avatar Vladimir Sementsov-Ogievskiy Committed by John Snow
Browse files

util/hbitmap: strict hbitmap_reset 



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: default avatarVladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: default avatarMax 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: default avatarJohn Snow <jsnow@redhat.com>
parent f22f553e

include/qemu/hbitmap.h

+5 −0
Original line number Diff line number Diff line
@@ -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);

tests/test-hbitmap.c

+1 −1
Original line number Diff line number Diff line
@@ -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);

}

util/hbitmap.c

+4 −0
Original line number Diff line number Diff line
@@ -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);