qcow2: Make distinction between zero cluster types obvious

Treat plain zero clusters differently from allocated ones, so that
we can simplify the logic of checking whether an offset is present.
Do this by splitting QCOW2_CLUSTER_ZERO into two new enums,
QCOW2_CLUSTER_ZERO_PLAIN and QCOW2_CLUSTER_ZERO_ALLOC.

I tried to arrange the enum so that we could use
'ret <= QCOW2_CLUSTER_ZERO_PLAIN' for all unallocated types, and
'ret >= QCOW2_CLUSTER_ZERO_ALLOC' for allocated types, although
I didn't actually end up taking advantage of the layout.

In many cases, this leads to simpler code, by properly combining
cases (sometimes, both zero types pair together, other times,
plain zero is more like unallocated while allocated zero is more
like normal).

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-id: 20170507000552.20847-7-eblake@redhat.com
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>

1 files changed, 18 insertions, 26 deletions

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index e639b341e5..7c06061aae 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -1028,18 +1028,17 @@ void qcow2_free_any_clusters(BlockDriverState *bs, uint64_t l2_entry,
         }
         break;
     case QCOW2_CLUSTER_NORMAL:
-    case QCOW2_CLUSTER_ZERO:
-        if (l2_entry & L2E_OFFSET_MASK) {
-            if (offset_into_cluster(s, l2_entry & L2E_OFFSET_MASK)) {
-                qcow2_signal_corruption(bs, false, -1, -1,
-                                        "Cannot free unaligned cluster %#llx",
-                                        l2_entry & L2E_OFFSET_MASK);
-            } else {
-                qcow2_free_clusters(bs, l2_entry & L2E_OFFSET_MASK,
-                                    nb_clusters << s->cluster_bits, type);
-            }
+    case QCOW2_CLUSTER_ZERO_ALLOC:
+        if (offset_into_cluster(s, l2_entry & L2E_OFFSET_MASK)) {
+            qcow2_signal_corruption(bs, false, -1, -1,
+                                    "Cannot free unaligned cluster %#llx",
+                                    l2_entry & L2E_OFFSET_MASK);
+        } else {
+            qcow2_free_clusters(bs, l2_entry & L2E_OFFSET_MASK,
+                                nb_clusters << s->cluster_bits, type);
         }
         break;
+    case QCOW2_CLUSTER_ZERO_PLAIN:
     case QCOW2_CLUSTER_UNALLOCATED:
         break;
     default:
@@ -1145,10 +1144,10 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
                     break;
 
                 case QCOW2_CLUSTER_NORMAL:
-                case QCOW2_CLUSTER_ZERO:
+                case QCOW2_CLUSTER_ZERO_ALLOC:
                     if (offset_into_cluster(s, offset)) {
-                        qcow2_signal_corruption(bs, true, -1, -1, "Data "
-                                                "cluster offset %#" PRIx64
+                        qcow2_signal_corruption(bs, true, -1, -1, "Cluster "
+                                                "allocation offset %#" PRIx64
                                                 " unaligned (L2 offset: %#"
                                                 PRIx64 ", L2 index: %#x)",
                                                 offset, l2_offset, j);
@@ -1157,11 +1156,7 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
                     }
 
                     cluster_index = offset >> s->cluster_bits;
-                    if (!cluster_index) {
-                        /* unallocated */
-                        refcount = 0;
-                        break;
-                    }
+                    assert(cluster_index);
                     if (addend != 0) {
                         ret = qcow2_update_cluster_refcount(bs,
                                     cluster_index, abs(addend), addend < 0,
@@ -1177,6 +1172,7 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
                     }
                     break;
 
+                case QCOW2_CLUSTER_ZERO_PLAIN:
                 case QCOW2_CLUSTER_UNALLOCATED:
                     refcount = 0;
                     break;
@@ -1443,12 +1439,7 @@ static int check_refcounts_l2(BlockDriverState *bs, BdrvCheckResult *res,
             }
             break;
 
-        case QCOW2_CLUSTER_ZERO:
-            if ((l2_entry & L2E_OFFSET_MASK) == 0) {
-                break;
-            }
-            /* fall through */
-
+        case QCOW2_CLUSTER_ZERO_ALLOC:
         case QCOW2_CLUSTER_NORMAL:
         {
             uint64_t offset = l2_entry & L2E_OFFSET_MASK;
@@ -1478,6 +1469,7 @@ static int check_refcounts_l2(BlockDriverState *bs, BdrvCheckResult *res,
             break;
         }
 
+        case QCOW2_CLUSTER_ZERO_PLAIN:
         case QCOW2_CLUSTER_UNALLOCATED:
             break;
 
@@ -1642,8 +1634,8 @@ static int check_oflag_copied(BlockDriverState *bs, BdrvCheckResult *res,
             uint64_t data_offset = l2_entry & L2E_OFFSET_MASK;
             QCow2ClusterType cluster_type = qcow2_get_cluster_type(l2_entry);
 
-            if ((cluster_type == QCOW2_CLUSTER_NORMAL) ||
-                ((cluster_type == QCOW2_CLUSTER_ZERO) && (data_offset != 0))) {
+            if (cluster_type == QCOW2_CLUSTER_NORMAL ||
+                cluster_type == QCOW2_CLUSTER_ZERO_ALLOC) {
                 ret = qcow2_get_refcount(bs,
                                          data_offset >> s->cluster_bits,
                                          &refcount);