qcow2: Move cluster gathering to a non-looping loop

This patch is mainly to separate the indentation change from the
semantic changes. All that really changes here is that everything moves
into a while loop, all 'goto done' become 'break' and at the end of the
loop a new 'break is inserted.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

block/qcow2-cluster.c

@@ -1147,79 +1147,85 @@ again:
     cluster_offset = 0;
     *host_offset = 0;
 
-    /*
-     * Now start gathering as many contiguous clusters as possible:
-     *
-     * 1. Check for overlaps with in-flight allocations
-     *
-     *      a) Overlap not in the first cluster -> shorten this request and let
-     *         the caller handle the rest in its next loop iteration.
-     *
-     *      b) Real overlaps of two requests. Yield and restart the search for
-     *         contiguous clusters (the situation could have changed while we
-     *         were sleeping)
-     *
-     *      c) TODO: Request starts in the same cluster as the in-flight
-     *         allocation ends. Shorten the COW of the in-fight allocation, set
-     *         cluster_offset to write to the same cluster and set up the right
-     *         synchronisation between the in-flight request and the new one.
-     */
-    cur_bytes = remaining;
-    ret = handle_dependencies(bs, start, &cur_bytes);
-    if (ret == -EAGAIN) {
-        goto again;
-    } else if (ret < 0) {
-        return ret;
-    } else {
-        /* handle_dependencies() may have decreased cur_bytes (shortened
-         * the allocations below) so that the next dependency is processed
-         * correctly during the next loop iteration. */
-    }
-
-    /*
-     * 2. Count contiguous COPIED clusters.
-     */
-    ret = handle_copied(bs, start, &cluster_offset, &cur_bytes, m);
-    if (ret < 0) {
-        return ret;
-    } else if (ret) {
-        if (!*host_offset) {
-            *host_offset = start_of_cluster(s, cluster_offset);
+    while (true) {
+        /*
+         * Now start gathering as many contiguous clusters as possible:
+         *
+         * 1. Check for overlaps with in-flight allocations
+         *
+         *      a) Overlap not in the first cluster -> shorten this request and
+         *         let the caller handle the rest in its next loop iteration.
+         *
+         *      b) Real overlaps of two requests. Yield and restart the search
+         *         for contiguous clusters (the situation could have changed
+         *         while we were sleeping)
+         *
+         *      c) TODO: Request starts in the same cluster as the in-flight
+         *         allocation ends. Shorten the COW of the in-fight allocation,
+         *         set cluster_offset to write to the same cluster and set up
+         *         the right synchronisation between the in-flight request and
+         *         the new one.
+         */
+        cur_bytes = remaining;
+        ret = handle_dependencies(bs, start, &cur_bytes);
+        if (ret == -EAGAIN) {
+            goto again;
+        } else if (ret < 0) {
+            return ret;
+        } else {
+            /* handle_dependencies() may have decreased cur_bytes (shortened
+             * the allocations below) so that the next dependency is processed
+             * correctly during the next loop iteration. */
         }
 
-        start           += cur_bytes;
-        remaining       -= cur_bytes;
-        cluster_offset  += cur_bytes;
+        /*
+         * 2. Count contiguous COPIED clusters.
+         */
+        ret = handle_copied(bs, start, &cluster_offset, &cur_bytes, m);
+        if (ret < 0) {
+            return ret;
+        } else if (ret) {
+            if (!*host_offset) {
+                *host_offset = start_of_cluster(s, cluster_offset);
+            }
 
-        cur_bytes = remaining;
-    } else if (cur_bytes == 0) {
-        goto done;
-    }
+            start           += cur_bytes;
+            remaining       -= cur_bytes;
+            cluster_offset  += cur_bytes;
 
-    /* If there is something left to allocate, do that now */
-    if (remaining == 0) {
-        goto done;
-    }
+            cur_bytes = remaining;
+        } else if (cur_bytes == 0) {
+            break;
+        }
 
-    /*
-     * 3. If the request still hasn't completed, allocate new clusters,
-     *    considering any cluster_offset of steps 1c or 2.
-     */
-    ret = handle_alloc(bs, start, &cluster_offset, &cur_bytes, m);
-    if (ret < 0) {
-        return ret;
-    } else if (ret) {
-        if (!*host_offset) {
-            *host_offset = start_of_cluster(s, cluster_offset);
+        /* If there is something left to allocate, do that now */
+        if (remaining == 0) {
+            break;
         }
 
-        start           += cur_bytes;
-        remaining       -= cur_bytes;
-        cluster_offset  += cur_bytes;
+        /*
+         * 3. If the request still hasn't completed, allocate new clusters,
+         *    considering any cluster_offset of steps 1c or 2.
+         */
+        ret = handle_alloc(bs, start, &cluster_offset, &cur_bytes, m);
+        if (ret < 0) {
+            return ret;
+        } else if (ret) {
+            if (!*host_offset) {
+                *host_offset = start_of_cluster(s, cluster_offset);
+            }
+
+            start           += cur_bytes;
+            remaining       -= cur_bytes;
+            cluster_offset  += cur_bytes;
+
+            break;
+        } else {
+            assert(cur_bytes == 0);
+            break;
+        }
     }
 
-    /* Some cleanup work */
-done:
     *num = (n_end - n_start) - (remaining >> BDRV_SECTOR_BITS);
     assert(*num > 0);
     assert(*host_offset != 0);