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qcow2: Fix qcow2_get_cluster_offset() for zero clusters

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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: Kevin Wolf <kwolf@redhat.com>
Message-id: 1446657384-5907-1-git-send-email-kwolf@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Kevin Wolf 2015-11-04 18:16:24 +01:00 committed by Max Reitz
parent 342075fd0e
commit a99dfb45f2
1 changed files with 9 additions and 6 deletions
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15
block/qcow2-cluster.c
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@ -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: