nbd/server: use bdrv_dirty_bitmap_next_dirty_area

Use bdrv_dirty_bitmap_next_dirty_area for bitmap_to_extents. Since
bdrv_dirty_bitmap_next_dirty_area is very accurate in its interface,
we'll never exceed requested region with last chunk. So, we don't need
dont_fragment, and bitmap_to_extents() interface becomes clean enough
to not require any comment.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 20200205112041.6003-10-vsementsov@virtuozzo.com
Signed-off-by: John Snow <jsnow@redhat.com>

nbd/server.c

@@ -2068,57 +2068,36 @@ static int nbd_co_send_block_status(NBDClient *client, uint64_t handle,
     return nbd_co_send_extents(client, handle, ea, last, context_id, errp);
 }
 
-/*
- * Populate @ea from a dirty bitmap. Unless @dont_fragment, the
- * final extent may exceed the original @length.
- */
+/* Populate @ea from a dirty bitmap. */
 static void bitmap_to_extents(BdrvDirtyBitmap *bitmap,
                               uint64_t offset, uint64_t length,
-                              NBDExtentArray *ea, bool dont_fragment)
+                              NBDExtentArray *es)
 {
-    uint64_t begin = offset, end = offset;
-    uint64_t overall_end = offset + length;
-    BdrvDirtyBitmapIter *it;
-    bool dirty;
+    int64_t start, dirty_start, dirty_count;
+    int64_t end = offset + length;
+    bool full = false;
 
     bdrv_dirty_bitmap_lock(bitmap);
 
-    it = bdrv_dirty_iter_new(bitmap);
-    dirty = bdrv_dirty_bitmap_get_locked(bitmap, offset);
-
-    while (begin < overall_end) {
-        bool next_dirty = !dirty;
-
-        if (dirty) {
-            end = bdrv_dirty_bitmap_next_zero(bitmap, begin, INT64_MAX);
-        } else {
-            bdrv_set_dirty_iter(it, begin);
-            end = bdrv_dirty_iter_next(it);
-        }
-        if (end == -1 || end - begin > UINT32_MAX) {
-            /* Cap to an aligned value < 4G beyond begin. */
-            end = MIN(bdrv_dirty_bitmap_size(bitmap),
-                      begin + UINT32_MAX + 1 -
-                      bdrv_dirty_bitmap_granularity(bitmap));
-            next_dirty = dirty;
-        }
-        if (dont_fragment && end > overall_end) {
-            end = overall_end;
-        }
-
-        if (nbd_extent_array_add(ea, end - begin,
-                                 dirty ? NBD_STATE_DIRTY : 0) < 0) {
+    for (start = offset;
+         bdrv_dirty_bitmap_next_dirty_area(bitmap, start, end, INT32_MAX,
+                                           &dirty_start, &dirty_count);
+         start = dirty_start + dirty_count)
+    {
+        if ((nbd_extent_array_add(es, dirty_start - start, 0) < 0) ||
+            (nbd_extent_array_add(es, dirty_count, NBD_STATE_DIRTY) < 0))
+        {
+            full = true;
             break;
         }
-        begin = end;
-        dirty = next_dirty;
     }
 
-    bdrv_dirty_iter_free(it);
+    if (!full) {
+        /* last non dirty extent */
+        nbd_extent_array_add(es, end - start, 0);
+    }
 
     bdrv_dirty_bitmap_unlock(bitmap);
-
-    assert(offset < end);
 }
 
 static int nbd_co_send_bitmap(NBDClient *client, uint64_t handle,
@@ -2129,7 +2108,7 @@ static int nbd_co_send_bitmap(NBDClient *client, uint64_t handle,
     unsigned int nb_extents = dont_fragment ? 1 : NBD_MAX_BLOCK_STATUS_EXTENTS;
     g_autoptr(NBDExtentArray) ea = nbd_extent_array_new(nb_extents);
 
-    bitmap_to_extents(bitmap, offset, length, ea, dont_fragment);
+    bitmap_to_extents(bitmap, offset, length, ea);
 
     return nbd_co_send_extents(client, handle, ea, last, context_id, errp);
 }