1 files changed, 84 insertions, 0 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index c22784b989b7..0c7f478cf645 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -728,6 +728,90 @@ error:
         return ret;
 }
 
+/* helper to account the used device space in the range */
+int btrfs_account_dev_extents_size(struct btrfs_device *device, u64 start,
+                                   u64 end, u64 *length)
+{
+        struct btrfs_key key;
+        struct btrfs_root *root = device->dev_root;
+        struct btrfs_dev_extent *dev_extent;
+        struct btrfs_path *path;
+        u64 extent_end;
+        int ret;
+        int slot;
+        struct extent_buffer *l;
+
+        *length = 0;
+
+        if (start >= device->total_bytes)
+                return 0;
+
+        path = btrfs_alloc_path();
+        if (!path)
+                return -ENOMEM;
+        path->reada = 2;
+
+        key.objectid = device->devid;
+        key.offset = start;
+        key.type = BTRFS_DEV_EXTENT_KEY;
+
+        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+        if (ret < 0)
+                goto out;
+        if (ret > 0) {
+                ret = btrfs_previous_item(root, path, key.objectid, key.type);
+                if (ret < 0)
+                        goto out;
+        }
+
+        while (1) {
+                l = path->nodes[0];
+                slot = path->slots[0];
+                if (slot >= btrfs_header_nritems(l)) {
+                        ret = btrfs_next_leaf(root, path);
+                        if (ret == 0)
+                                continue;
+                        if (ret < 0)
+                                goto out;
+
+                        break;
+                }
+                btrfs_item_key_to_cpu(l, &key, slot);
+
+                if (key.objectid < device->devid)
+                        goto next;
+
+                if (key.objectid > device->devid)
+                        break;
+
+                if (btrfs_key_type(&key) != BTRFS_DEV_EXTENT_KEY)
+                        goto next;
+
+                dev_extent = btrfs_item_ptr(l, slot, struct btrfs_dev_extent);
+                extent_end = key.offset + btrfs_dev_extent_length(l,
+                                                                  dev_extent);
+                if (key.offset <= start && extent_end > end) {
+                        *length = end - start + 1;
+                        break;
+                } else if (key.offset <= start && extent_end > start)
+                        *length += extent_end - start;
+                else if (key.offset > start && extent_end <= end)
+                        *length += extent_end - key.offset;
+                else if (key.offset > start && key.offset <= end) {
+                        *length += end - key.offset + 1;
+                        break;
+                } else if (key.offset > end)
+                        break;
+
+next:
+                path->slots[0]++;
+        }
+        ret = 0;
+out:
+        btrfs_free_path(path);
+        return ret;
+}
+
 /*
  * find_free_dev_extent - find free space in the specified device
  * @trans:      transaction handler