qed: Add support for zero clusters

Zero clusters are similar to unallocated clusters except instead of reading
their value from a backing file when one is available, the cluster is always
read as zero.

This implements read support only.  At this stage, QED will never write a
zero cluster.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 21 insertions, 10 deletions

diff --git a/block/qed-cluster.c b/block/qed-cluster.c
index 0ec864b14c..3e19ad1766 100644
--- a/block/qed-cluster.c
+++ b/block/qed-cluster.c
@@ -23,7 +23,8 @@
  * @n:              Maximum number of clusters
  * @offset:         Set to first cluster offset
  *
- * This function scans tables for contiguous allocated or free clusters.
+ * This function scans tables for contiguous clusters.  A contiguous run of
+ * clusters may be allocated, unallocated, or zero.
  */
 static unsigned int qed_count_contiguous_clusters(BDRVQEDState *s,
                                                   QEDTable *table,
@@ -38,9 +39,14 @@ static unsigned int qed_count_contiguous_clusters(BDRVQEDState *s,
     *offset = last;
 
     for (i = index + 1; i < end; i++) {
-        if (last == 0) {
-            /* Counting free clusters */
-            if (table->offsets[i] != 0) {
+        if (qed_offset_is_unalloc_cluster(last)) {
+            /* Counting unallocated clusters */
+            if (!qed_offset_is_unalloc_cluster(table->offsets[i])) {
+                break;
+            }
+        } else if (qed_offset_is_zero_cluster(last)) {
+            /* Counting zero clusters */
+            if (!qed_offset_is_zero_cluster(table->offsets[i])) {
                 break;
             }
         } else {
@@ -87,14 +93,19 @@ static void qed_find_cluster_cb(void *opaque, int ret)
     n = qed_count_contiguous_clusters(s, request->l2_table->table,
                                       index, n, &offset);
 
-    ret = offset ? QED_CLUSTER_FOUND : QED_CLUSTER_L2;
-    len = MIN(find_cluster_cb->len, n * s->header.cluster_size -
-              qed_offset_into_cluster(s, find_cluster_cb->pos));
-
-    if (offset && !qed_check_cluster_offset(s, offset)) {
+    if (qed_offset_is_unalloc_cluster(offset)) {
+        ret = QED_CLUSTER_L2;
+    } else if (qed_offset_is_zero_cluster(offset)) {
+        ret = QED_CLUSTER_ZERO;
+    } else if (qed_check_cluster_offset(s, offset)) {
+        ret = QED_CLUSTER_FOUND;
+    } else {
         ret = -EINVAL;
     }
 
+    len = MIN(find_cluster_cb->len, n * s->header.cluster_size -
+              qed_offset_into_cluster(s, find_cluster_cb->pos));
+
 out:
     find_cluster_cb->cb(find_cluster_cb->opaque, ret, offset, len);
     qemu_free(find_cluster_cb);
@@ -132,7 +143,7 @@ void qed_find_cluster(BDRVQEDState *s, QEDRequest *request, uint64_t pos,
     len = MIN(len, (((pos >> s->l1_shift) + 1) << s->l1_shift) - pos);
 
     l2_offset = s->l1_table->offsets[qed_l1_index(s, pos)];
-    if (!l2_offset) {
+    if (qed_offset_is_unalloc_cluster(l2_offset)) {
         cb(opaque, QED_CLUSTER_L1, 0, len);
         return;
     }