1 files changed, 57 insertions, 0 deletions

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 6b76fd967153..43d4779abdd1 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -1249,6 +1249,63 @@ static int split_leaf(struct btrfs_trans_handle *trans, struct btrfs_root
         return ret;
 }
 
+int btrfs_truncate_item(struct btrfs_trans_handle *trans,
+                        struct btrfs_root *root,
+                        struct btrfs_path *path,
+                        u32 new_size)
+{
+        int ret = 0;
+        int slot;
+        int slot_orig;
+        struct btrfs_leaf *leaf;
+        struct buffer_head *leaf_buf;
+        u32 nritems;
+        unsigned int data_end;
+        unsigned int old_data_start;
+        unsigned int old_size;
+        unsigned int size_diff;
+        int i;
+
+        slot_orig = path->slots[0];
+        leaf_buf = path->nodes[0];
+        leaf = btrfs_buffer_leaf(leaf_buf);
+
+        nritems = btrfs_header_nritems(&leaf->header);
+        data_end = leaf_data_end(root, leaf);
+
+        slot = path->slots[0];
+        old_data_start = btrfs_item_offset(leaf->items + slot);
+        old_size = btrfs_item_size(leaf->items + slot);
+        BUG_ON(old_size <= new_size);
+        size_diff = old_size - new_size;
+
+        BUG_ON(slot < 0);
+        BUG_ON(slot >= nritems);
+
+        /*
+         * item0..itemN ... dataN.offset..dataN.size .. data0.size
+         */
+        /* first correct the data pointers */
+        for (i = slot; i < nritems; i++) {
+                u32 ioff = btrfs_item_offset(leaf->items + i);
+                btrfs_set_item_offset(leaf->items + i,
+                                      ioff + size_diff);
+        }
+        /* shift the data */
+printk("truncate item, new_size %u old_size %u, diff %u, bufp %p, dst, %p, num %u, old_data_start %u, data_end %u\n", new_size, old_size, size_diff, leaf, btrfs_leaf_data(leaf) + data_end + size_diff, old_data_start-data_end, old_data_start, data_end);
+        btrfs_memmove(root, leaf, btrfs_leaf_data(leaf) +
+                      data_end + size_diff, btrfs_leaf_data(leaf) +
+                      data_end, old_data_start + new_size - data_end);
+        btrfs_set_item_size(leaf->items + slot, new_size);
+        btrfs_mark_buffer_dirty(leaf_buf);
+
+        ret = 0;
+        if (btrfs_leaf_free_space(root, leaf) < 0)
+                BUG();
+        check_leaf(root, path, 0);
+        return ret;
+}
+
 int btrfs_extend_item(struct btrfs_trans_handle *trans, struct btrfs_root
                       *root, struct btrfs_path *path, u32 data_size)
 {