[RFC PATCH 14/23] qcow2: Add subcluster support to qcow2_get_cluster_offset()

[Alberto Garcia <berto@igalia.com>]

The logic of this function remains pretty much the same, except that
it uses count_contiguous_subclusters(), which combines the logic of
count_contiguous_clusters() / count_contiguous_clusters_unallocated()
and checks individual subclusters.

Signed-off-by: Alberto Garcia <berto@igalia.com>
---
 block/qcow2-cluster.c | 111 ++++++++++++++++++++----------------------
 1 file changed, 52 insertions(+), 59 deletions(-)

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 8df0f67316..71d4cc518a 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -372,66 +372,51 @@ fail:
 }
 
 /*
- * Checks how many clusters in a given L2 slice are contiguous in the image
- * file. As soon as one of the flags in the bitmask stop_flags changes compared
- * to the first cluster, the search is stopped and the cluster is not counted
- * as contiguous. (This allows it, for example, to stop at the first compressed
- * cluster which may require a different handling)
+ * Return the number of contiguous subclusters of the exact same type
+ * in a given L2 slice, starting from cluster @l2_index, subcluster
+ * @sc_index. At most @nb_clusters are checked. Allocated clusters are
+ * also required to be contiguous in the image file.
  */
-static int count_contiguous_clusters(BlockDriverState *bs, int nb_clusters,
-        int cluster_size, uint64_t *l2_slice, int l2_index, uint64_t stop_flags)
+static int count_contiguous_subclusters(BlockDriverState *bs, int nb_clusters,
+                                        unsigned sc_index, uint64_t *l2_slice,
+                                        int l2_index)
 {
     BDRVQcow2State *s = bs->opaque;
-    int i;
-    QCow2ClusterType first_cluster_type;
-    uint64_t mask = stop_flags | L2E_OFFSET_MASK | QCOW_OFLAG_COMPRESSED;
-    uint64_t first_entry = get_l2_entry(s, l2_slice, l2_index);
-    uint64_t offset = first_entry & mask;
-
-    first_cluster_type = qcow2_get_cluster_type(bs, first_entry);
-    if (first_cluster_type == QCOW2_CLUSTER_UNALLOCATED) {
-        return 0;
+    int i, j, count = 0;
+    uint64_t l2_entry = get_l2_entry(s, l2_slice, l2_index);
+    uint64_t l2_bitmap = get_l2_bitmap(s, l2_slice, l2_index);
+    uint64_t expected_offset = l2_entry & L2E_OFFSET_MASK;
+    bool check_offset = true;
+    QCow2ClusterType type =
+        qcow2_get_subcluster_type(bs, l2_entry, l2_bitmap, sc_index);
+
+    assert(type != QCOW2_CLUSTER_INVALID); /* The caller should check this */
+
+    if (type == QCOW2_CLUSTER_COMPRESSED) {
+        return 1; /* Compressed clusters are always counted one by one */
     }
 
-    /* must be allocated */
-    assert(first_cluster_type == QCOW2_CLUSTER_NORMAL ||
-           first_cluster_type == QCOW2_CLUSTER_ZERO_ALLOC);
-
-    for (i = 0; i < nb_clusters; i++) {
-        uint64_t l2_entry = get_l2_entry(s, l2_slice, l2_index + i) & mask;
-        if (offset + (uint64_t) i * cluster_size != l2_entry) {
-            break;
-        }
+    if (type == QCOW2_CLUSTER_UNALLOCATED || type == QCOW2_CLUSTER_ZERO_PLAIN) {
+        check_offset = false;
     }
 
-        return i;
-}
-
-/*
- * Checks how many consecutive unallocated clusters in a given L2
- * slice have the same cluster type.
- */
-static int count_contiguous_clusters_unallocated(BlockDriverState *bs,
-                                                 int nb_clusters,
-                                                 uint64_t *l2_slice,
-                                                 int l2_index,
-                                                 QCow2ClusterType wanted_type)
-{
-    BDRVQcow2State *s = bs->opaque;
-    int i;
-
-    assert(wanted_type == QCOW2_CLUSTER_ZERO_PLAIN ||
-           wanted_type == QCOW2_CLUSTER_UNALLOCATED);
     for (i = 0; i < nb_clusters; i++) {
-        uint64_t entry = get_l2_entry(s, l2_slice, l2_index + i);
-        QCow2ClusterType type = qcow2_get_cluster_type(bs, entry);
-
-        if (type != wanted_type) {
-            break;
+        l2_entry = get_l2_entry(s, l2_slice, l2_index + i);
+        l2_bitmap = get_l2_bitmap(s, l2_slice, l2_index + i);
+        if (check_offset && expected_offset != (l2_entry & L2E_OFFSET_MASK)) {
+            goto out;
+        }
+        for (j = (i == 0) ? sc_index : 0; j < s->subclusters_per_cluster; j++) {
+            if (qcow2_get_subcluster_type(bs, l2_entry, l2_bitmap, j) != type) {
+                goto out;
+            }
+            count++;
         }
+        expected_offset += s->cluster_size;
     }
 
-    return i;
+out:
+    return count;
 }
 
 static int coroutine_fn do_perform_cow_read(BlockDriverState *bs,
@@ -514,8 +499,8 @@ int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset,
                              unsigned int *bytes, uint64_t *cluster_offset)
 {
     BDRVQcow2State *s = bs->opaque;
-    unsigned int l2_index;
-    uint64_t l1_index, l2_offset, *l2_slice;
+    unsigned int l2_index, sc_index;
+    uint64_t l1_index, l2_offset, *l2_slice, l2_bitmap;
     int c;
     unsigned int offset_in_cluster;
     uint64_t bytes_available, bytes_needed, nb_clusters;
@@ -569,7 +554,9 @@ int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset,
     /* find the cluster offset for the given disk offset */
 
     l2_index = offset_to_l2_slice_index(s, offset);
+    sc_index = offset_to_sc_index(s, offset);
     *cluster_offset = get_l2_entry(s, l2_slice, l2_index);
+    l2_bitmap = get_l2_bitmap(s, l2_slice, l2_index);
 
     nb_clusters = size_to_clusters(s, bytes_needed);
     /* bytes_needed <= *bytes + offset_in_cluster, both of which are unsigned
@@ -577,7 +564,7 @@ int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset,
      * true */
     assert(nb_clusters <= INT_MAX);
 
-    type = qcow2_get_cluster_type(bs, *cluster_offset);
+    type = qcow2_get_subcluster_type(bs, *cluster_offset, l2_bitmap, sc_index);
     if (s->qcow_version < 3 && (type == QCOW2_CLUSTER_ZERO_PLAIN ||
                                 type == QCOW2_CLUSTER_ZERO_ALLOC)) {
         qcow2_signal_corruption(bs, true, -1, -1, "Zero cluster entry found"
@@ -587,6 +574,13 @@ int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset,
         goto fail;
     }
     switch (type) {
+    case QCOW2_CLUSTER_INVALID:
+        qcow2_signal_corruption(bs, true, -1, -1, "Invalid cluster entry found "
+                                " (L2 offset: %#" PRIx64 ", L2 index: %#x)",
+                                l2_offset, l2_index);
+        ret = -EIO;
+        goto fail;
+        break;
     case QCOW2_CLUSTER_COMPRESSED:
         if (has_data_file(bs)) {
             qcow2_signal_corruption(bs, true, -1, -1, "Compressed cluster "
@@ -602,16 +596,15 @@ int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset,
         break;
     case QCOW2_CLUSTER_ZERO_PLAIN:
     case QCOW2_CLUSTER_UNALLOCATED:
-        /* how many empty clusters ? */
-        c = count_contiguous_clusters_unallocated(bs, nb_clusters,
-                                                  l2_slice, l2_index, type);
+        c = count_contiguous_subclusters(bs, nb_clusters, sc_index,
+                                         l2_slice, l2_index);
         *cluster_offset = 0;
         break;
     case QCOW2_CLUSTER_ZERO_ALLOC:
     case QCOW2_CLUSTER_NORMAL:
-        /* how many allocated clusters ? */
-        c = count_contiguous_clusters(bs, nb_clusters, s->cluster_size,
-                                      l2_slice, l2_index, QCOW_OFLAG_ZERO);
+    case QCOW2_CLUSTER_UNALLOCATED_SUBCLUSTER:
+        c = count_contiguous_subclusters(bs, nb_clusters, sc_index,
+                                         l2_slice, l2_index);
         *cluster_offset &= L2E_OFFSET_MASK;
         if (offset_into_cluster(s, *cluster_offset)) {
             qcow2_signal_corruption(bs, true, -1, -1,
@@ -640,7 +633,7 @@ int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset,
 
     qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
 
-    bytes_available = (int64_t)c * s->cluster_size;
+    bytes_available = ((int64_t)c + sc_index) * s->subcluster_size;
 
 out:
     if (bytes_available > bytes_needed) {
-- 
2.20.1