Commit 20a579de authored by Max Reitz's avatar Max Reitz Committed by Fam Zheng
Browse files

hbitmap: Add hbitmap_is_serializable() 



Bitmaps with a granularity of 58 or above can be neither serialized nor
deserialized (see the comment in the function added in this series for
an explanation). This patch adds a function so that we can check whether
a bitmap actually can be (de-)serialized at all, thus avoiding failing
the necessary assertion in hbitmap_serialization_granularity().

Signed-off-by: default avatarMax Reitz <mreitz@redhat.com>
Message-Id: <20161115225746.3590-2-mreitz@redhat.com>
Reviewed-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: default avatarFam Zheng <famz@redhat.com>
parent c7f1cf01

include/qemu/hbitmap.h

+13 −0
Original line number Diff line number Diff line
@@ -145,6 +145,19 @@ void hbitmap_reset_all(HBitmap *hb); 
 */

bool hbitmap_get(const HBitmap *hb, uint64_t item);



/**

 * hbitmap_is_serializable:

 * @hb: HBitmap which should be (de-)serialized.

 *

 * Returns whether the bitmap can actually be (de-)serialized. Other

 * (de-)serialization functions may only be invoked if this function returns

 * true.

 *

 * Calling (de-)serialization functions does not affect a bitmap's

 * (de-)serializability.

 */

bool hbitmap_is_serializable(const HBitmap *hb);



/**

 * hbitmap_serialization_granularity:

 * @hb: HBitmap to operate on.

util/hbitmap.c

+19 −3
Original line number Diff line number Diff line
@@ -387,6 +387,24 @@ void hbitmap_reset_all(HBitmap *hb) 
    hb->count = 0;

}



bool hbitmap_is_serializable(const HBitmap *hb)

{

    /* Every serialized chunk must be aligned to 64 bits so that endianness

     * requirements can be fulfilled on both 64 bit and 32 bit hosts.

     * We have hbitmap_serialization_granularity() which converts this

     * alignment requirement from bitmap bits to items covered (e.g. sectors).

     * That value is:

     *    64 << hb->granularity

     * Since this value must not exceed UINT64_MAX, hb->granularity must be

     * less than 58 (== 64 - 6, where 6 is ld(64), i.e. 1 << 6 == 64).

     *

     * In order for hbitmap_serialization_granularity() to always return a

     * meaningful value, bitmaps that are to be serialized must have a

     * granularity of less than 58. */



    return hb->granularity < 58;

}



bool hbitmap_get(const HBitmap *hb, uint64_t item)

{

    /* Compute position and bit in the last layer.  */
@@ -399,9 +417,7 @@ bool hbitmap_get(const HBitmap *hb, uint64_t item) 


uint64_t hbitmap_serialization_granularity(const HBitmap *hb)

{

    /* Must hold true so that the shift below is defined

     * (ld(64) == 6, i.e. 1 << 6 == 64) */

    assert(hb->granularity < 64 - 6);

    assert(hbitmap_is_serializable(hb));



    /* Require at least 64 bit granularity to be safe on both 64 bit and 32 bit

     * hosts. */