Commit a99dfb45 authored by Kevin Wolf's avatar Kevin Wolf Committed by Max Reitz
Browse files

qcow2: Fix qcow2_get_cluster_offset() for zero clusters 



When searching for contiguous zero clusters, we only need to check the
cluster type. Before this patch, an increasing offset (L2E_OFFSET_MASK)
was expected, so that the function never returned more than a single
zero cluster in practice. This patch fixes it to actually return as many
contiguous zero clusters as it can.

Cc: qemu-stable@nongnu.org
Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
Message-id: 1446657384-5907-1-git-send-email-kwolf@redhat.com
Signed-off-by: default avatarMax Reitz <mreitz@redhat.com>
parent 342075fd

block/qcow2-cluster.c

+9 −6
Original line number Diff line number Diff line
@@ -312,7 +312,7 @@ static int count_contiguous_clusters(int nb_clusters, int cluster_size, 
    if (!offset)

        return 0;



    assert(qcow2_get_cluster_type(first_entry) != QCOW2_CLUSTER_COMPRESSED);

    assert(qcow2_get_cluster_type(first_entry) == QCOW2_CLUSTER_NORMAL);



    for (i = 0; i < nb_clusters; i++) {

        uint64_t l2_entry = be64_to_cpu(l2_table[i]) & mask;
@@ -324,14 +324,16 @@ static int count_contiguous_clusters(int nb_clusters, int cluster_size, 
	return i;

}



static int count_contiguous_free_clusters(int nb_clusters, uint64_t *l2_table)

static int count_contiguous_clusters_by_type(int nb_clusters,

                                             uint64_t *l2_table,

                                             int wanted_type)

{

    int i;



    for (i = 0; i < nb_clusters; i++) {

        int type = qcow2_get_cluster_type(be64_to_cpu(l2_table[i]));



        if (type != QCOW2_CLUSTER_UNALLOCATED) {

        if (type != wanted_type) {

            break;

        }

    }
@@ -554,13 +556,14 @@ int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset, 
            ret = -EIO;

            goto fail;

        }

        c = count_contiguous_clusters(nb_clusters, s->cluster_size,

                &l2_table[l2_index], QCOW_OFLAG_ZERO);

        c = count_contiguous_clusters_by_type(nb_clusters, &l2_table[l2_index],

                                              QCOW2_CLUSTER_ZERO);

        *cluster_offset = 0;

        break;

    case QCOW2_CLUSTER_UNALLOCATED:

        /* how many empty clusters ? */

        c = count_contiguous_free_clusters(nb_clusters, &l2_table[l2_index]);

        c = count_contiguous_clusters_by_type(nb_clusters, &l2_table[l2_index],

                                              QCOW2_CLUSTER_UNALLOCATED);

        *cluster_offset = 0;

        break;

    case QCOW2_CLUSTER_NORMAL: