Btrfs: early work to file_write in big extents

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 54 insertions, 0 deletions

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index e2fc6f0d0243..6b76fd967153 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -1249,6 +1249,60 @@ static int split_leaf(struct btrfs_trans_handle *trans, struct btrfs_root
         return ret;
 }
 
+int btrfs_extend_item(struct btrfs_trans_handle *trans, struct btrfs_root
+                      *root, struct btrfs_path *path, u32 data_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;
+        unsigned int old_size;
+        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);
+
+        if (btrfs_leaf_free_space(root, leaf) < data_size)
+                BUG();
+        slot = path->slots[0];
+        old_data = btrfs_item_end(leaf->items + slot);
+
+        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 - data_size);
+        }
+        /* shift the data */
+        btrfs_memmove(root, leaf, btrfs_leaf_data(leaf) +
+                      data_end - data_size, btrfs_leaf_data(leaf) +
+                      data_end, old_data - data_end);
+        data_end = old_data;
+        old_size = btrfs_item_size(leaf->items + slot);
+        btrfs_set_item_size(leaf->items + slot, old_size + data_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;
+}
+
 /*
  * Given a key and some data, insert an item into the tree.
  * This does all the path init required, making room in the tree if needed.