qcow2: Rewrite qcow2_alloc_bytes()

qcow2_alloc_bytes() is a function with insufficient error handling and
an unnecessary goto. This patch rewrites it.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/qcow2-refcount.c

@@ -759,54 +759,54 @@ int qcow2_alloc_clusters_at(BlockDriverState *bs, uint64_t offset,
 int64_t qcow2_alloc_bytes(BlockDriverState *bs, int size)
 {
     BDRVQcowState *s = bs->opaque;
-    int64_t offset, cluster_offset;
-    int free_in_cluster;
+    int64_t offset;
+    size_t free_in_cluster;
+    int ret;
 
     BLKDBG_EVENT(bs->file, BLKDBG_CLUSTER_ALLOC_BYTES);
     assert(size > 0 && size <= s->cluster_size);
-    if (s->free_byte_offset == 0) {
-        offset = qcow2_alloc_clusters(bs, s->cluster_size);
-        if (offset < 0) {
-            return offset;
+    assert(!s->free_byte_offset || offset_into_cluster(s, s->free_byte_offset));
+
+    offset = s->free_byte_offset;
+
+    if (offset) {
+        int refcount = qcow2_get_refcount(bs, offset >> s->cluster_bits);
+        if (refcount < 0) {
+            return refcount;
         }
-        s->free_byte_offset = offset;
-    }
- redo:
-    free_in_cluster = s->cluster_size -
-        offset_into_cluster(s, s->free_byte_offset);
-    if (size <= free_in_cluster) {
-        /* enough space in current cluster */
-        offset = s->free_byte_offset;
-        s->free_byte_offset += size;
-        free_in_cluster -= size;
-        if (free_in_cluster == 0)
-            s->free_byte_offset = 0;
-        if (offset_into_cluster(s, offset) != 0)
-            qcow2_update_cluster_refcount(bs, offset >> s->cluster_bits, 1,
-                                          QCOW2_DISCARD_NEVER);
-    } else {
-        offset = qcow2_alloc_clusters(bs, s->cluster_size);
-        if (offset < 0) {
-            return offset;
+
+        if (refcount == 0xffff) {
+            offset = 0;
         }
-        cluster_offset = start_of_cluster(s, s->free_byte_offset);
-        if ((cluster_offset + s->cluster_size) == offset) {
-            /* we are lucky: contiguous data */
-            offset = s->free_byte_offset;
-            qcow2_update_cluster_refcount(bs, offset >> s->cluster_bits, 1,
-                                          QCOW2_DISCARD_NEVER);
-            s->free_byte_offset += size;
-        } else {
-            s->free_byte_offset = offset;
-            goto redo;
+    }
+
+    free_in_cluster = s->cluster_size - offset_into_cluster(s, offset);
+    if (!offset || free_in_cluster < size) {
+        int64_t new_cluster = alloc_clusters_noref(bs, s->cluster_size);
+        if (new_cluster < 0) {
+            return new_cluster;
+        }
+
+        if (!offset || ROUND_UP(offset, s->cluster_size) != new_cluster) {
+            offset = new_cluster;
         }
     }
 
-    /* The cluster refcount was incremented, either by qcow2_alloc_clusters()
-     * or explicitly by qcow2_update_cluster_refcount().  Refcount blocks must
-     * be flushed before the caller's L2 table updates.
-     */
+    assert(offset);
+    ret = update_refcount(bs, offset, size, 1, QCOW2_DISCARD_NEVER);
+    if (ret < 0) {
+        return ret;
+    }
+
+    /* The cluster refcount was incremented; refcount blocks must be flushed
+     * before the caller's L2 table updates. */
     qcow2_cache_set_dependency(bs, s->l2_table_cache, s->refcount_block_cache);
+
+    s->free_byte_offset = offset + size;
+    if (!offset_into_cluster(s, s->free_byte_offset)) {
+        s->free_byte_offset = 0;
+    }
+
     return offset;
 }