Commit d1dde714 authored by Eric Blake's avatar Eric Blake Committed by John Snow
Browse files

bitmap: Update count after a merge 



We need an accurate count of the number of bits set in a bitmap
after a merge. In particular, since the merge operation short-circuits
a merge from an empty source, if you have bitmaps A, B, and C where
B started empty, then merge C into B, and B into A, an inaccurate
count meant that A did not get the contents of C.

In the worst case, we may falsely regard the bitmap as empty when
it has had new writes merged into it.

Fixes: be58721d
CC: qemu-stable@nongnu.org
Signed-off-by: default avatarEric Blake <eblake@redhat.com>
Signed-off-by: default avatarJohn Snow <jsnow@redhat.com>
Reviewed-by: default avatarVladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-id: 20181002233314.30159-1-jsnow@redhat.com
Signed-off-by: default avatarJohn Snow <jsnow@redhat.com>
parent d9782022

util/hbitmap.c

+3 −0
Original line number Diff line number Diff line
@@ -759,6 +759,9 @@ bool hbitmap_merge(const HBitmap *a, const HBitmap *b, HBitmap *result) 
        }

    }



    /* Recompute the dirty count */

    result->count = hb_count_between(result, 0, result->size - 1);



    return true;

}