1 files changed, 192 insertions, 34 deletions

diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c
index a3ad2ce0011..3ebef871ee6 100644
--- a/fs/btrfs/file-item.c
+++ b/fs/btrfs/file-item.c
@@ -310,6 +310,179 @@ int btrfs_csum_one_bio(struct btrfs_root *root, struct inode *inode,
         return 0;
 }
 
+/*
+ * helper function for csum removal, this expects the
+ * key to describe the csum pointed to by the path, and it expects
+ * the csum to overlap the range [bytenr, len]
+ *
+ * The csum should not be entirely contained in the range and the
+ * range should not be entirely contained in the csum.
+ *
+ * This calls btrfs_truncate_item with the correct args based on the
+ * overlap, and fixes up the key as required.
+ */
+static noinline int truncate_one_csum(struct btrfs_trans_handle *trans,
+                                      struct btrfs_root *root,
+                                      struct btrfs_path *path,
+                                      struct btrfs_key *key,
+                                      u64 bytenr, u64 len)
+{
+        struct extent_buffer *leaf;
+        u16 csum_size =
+                btrfs_super_csum_size(&root->fs_info->super_copy);
+        u64 csum_end;
+        u64 end_byte = bytenr + len;
+        u32 blocksize_bits = root->fs_info->sb->s_blocksize_bits;
+        int ret;
+
+        leaf = path->nodes[0];
+        csum_end = btrfs_item_size_nr(leaf, path->slots[0]) / csum_size;
+        csum_end <<= root->fs_info->sb->s_blocksize_bits;
+        csum_end += key->offset;
+
+        if (key->offset < bytenr && csum_end <= end_byte) {
+                /*
+                 *         [ bytenr - len ]
+                 *         [   ]
+                 *   [csum     ]
+                 *   A simple truncate off the end of the item
+                 */
+                u32 new_size = (bytenr - key->offset) >> blocksize_bits;
+                new_size *= csum_size;
+                ret = btrfs_truncate_item(trans, root, path, new_size, 1);
+                BUG_ON(ret);
+        } else if (key->offset >= bytenr && csum_end > end_byte &&
+                   end_byte > key->offset) {
+                /*
+                 *         [ bytenr - len ]
+                 *                 [ ]
+                 *                 [csum     ]
+                 * we need to truncate from the beginning of the csum
+                 */
+                u32 new_size = (csum_end - end_byte) >> blocksize_bits;
+                new_size *= csum_size;
+
+                ret = btrfs_truncate_item(trans, root, path, new_size, 0);
+                BUG_ON(ret);
+
+                key->offset = end_byte;
+                ret = btrfs_set_item_key_safe(trans, root, path, key);
+                BUG_ON(ret);
+        } else {
+                BUG();
+        }
+        return 0;
+}
+
+/*
+ * deletes the csum items from the csum tree for a given
+ * range of bytes.
+ */
+int btrfs_del_csums(struct btrfs_trans_handle *trans,
+                    struct btrfs_root *root, u64 bytenr, u64 len)
+{
+        struct btrfs_path *path;
+        struct btrfs_key key;
+        u64 end_byte = bytenr + len;
+        u64 csum_end;
+        struct extent_buffer *leaf;
+        int ret;
+        u16 csum_size =
+                btrfs_super_csum_size(&root->fs_info->super_copy);
+        int blocksize_bits = root->fs_info->sb->s_blocksize_bits;
+
+        root = root->fs_info->csum_root;
+
+        path = btrfs_alloc_path();
+
+        while(1) {
+                key.objectid = BTRFS_EXTENT_CSUM_OBJECTID;
+                key.offset = end_byte - 1;
+                key.type = BTRFS_EXTENT_CSUM_KEY;
+
+                ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
+                if (ret > 0) {
+                        if (path->slots[0] == 0)
+                                goto out;
+                        path->slots[0]--;
+                }
+                leaf = path->nodes[0];
+                btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
+
+                if (key.objectid != BTRFS_EXTENT_CSUM_OBJECTID ||
+                    key.type != BTRFS_EXTENT_CSUM_KEY) {
+                        break;
+                }
+
+                if (key.offset >= end_byte)
+                        break;
+
+                csum_end = btrfs_item_size_nr(leaf, path->slots[0]) / csum_size;
+                csum_end <<= blocksize_bits;
+                csum_end += key.offset;
+
+                /* this csum ends before we start, we're done */
+                if (csum_end <= bytenr)
+                        break;
+
+                /* delete the entire item, it is inside our range */
+                if (key.offset >= bytenr && csum_end <= end_byte) {
+                        ret = btrfs_del_item(trans, root, path);
+                        BUG_ON(ret);
+                } else if (key.offset < bytenr && csum_end > end_byte) {
+                        unsigned long offset;
+                        unsigned long shift_len;
+                        unsigned long item_offset;
+                        /*
+                         *        [ bytenr - len ]
+                         *     [csum                ]
+                         *
+                         * Our bytes are in the middle of the csum,
+                         * we need to split this item and insert a new one.
+                         *
+                         * But we can't drop the path because the
+                         * csum could change, get removed, extended etc.
+                         *
+                         * The trick here is the max size of a csum item leaves
+                         * enough room in the tree block for a single
+                         * item header.  So, we split the item in place,
+                         * adding a new header pointing to the existing
+                         * bytes.  Then we loop around again and we have
+                         * a nicely formed csum item that we can neatly
+                         * truncate.
+                         */
+                        offset = (bytenr - key.offset) >> blocksize_bits;
+                        offset *= csum_size;
+
+                        shift_len = (len >> blocksize_bits) * csum_size;
+
+                        item_offset = btrfs_item_ptr_offset(leaf,
+                                                            path->slots[0]);
+
+                        memset_extent_buffer(leaf, 0, item_offset + offset,
+                                             shift_len);
+                        key.offset = bytenr;
+
+                        /*
+                         * btrfs_split_item returns -EAGAIN when the
+                         * item changed size or key
+                         */
+                        ret = btrfs_split_item(trans, root, path, &key, offset);
+                        BUG_ON(ret && ret != -EAGAIN);
+
+                        key.offset = end_byte - 1;
+                } else {
+                        ret = truncate_one_csum(trans, root, path,
+                                                &key, bytenr, len);
+                        BUG_ON(ret);
+                }
+                btrfs_release_path(root, path);
+        }
+out:
+        btrfs_free_path(path);
+        return 0;
+}
+
 int btrfs_csum_file_blocks(struct btrfs_trans_handle *trans,
                            struct btrfs_root *root,
                            struct btrfs_ordered_sum *sums)
@@ -396,28 +569,40 @@ again:
                                 csum_size, 1);
         if (ret < 0)
                 goto fail_unlock;
-        if (ret == 0) {
-                BUG();
-        }
-        if (path->slots[0] == 0) {
-                goto insert;
+
+        if (ret > 0) {
+                if (path->slots[0] == 0)
+                        goto insert;
+                path->slots[0]--;
         }
-        path->slots[0]--;
+
         leaf = path->nodes[0];
         btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
         csum_offset = (bytenr - found_key.offset) >>
                         root->fs_info->sb->s_blocksize_bits;
+
         if (btrfs_key_type(&found_key) != BTRFS_EXTENT_CSUM_KEY ||
             found_key.objectid != BTRFS_EXTENT_CSUM_OBJECTID ||
             csum_offset >= MAX_CSUM_ITEMS(root, csum_size)) {
                 goto insert;
         }
+
         if (csum_offset >= btrfs_item_size_nr(leaf, path->slots[0]) /
             csum_size) {
                 u32 diff = (csum_offset + 1) * csum_size;
+
+                /*
+                 * is the item big enough already?  we dropped our lock
+                 * before and need to recheck
+                 */
+                if (diff < btrfs_item_size_nr(leaf, path->slots[0]))
+                        goto csum;
+
                 diff = diff - btrfs_item_size_nr(leaf, path->slots[0]);
-                if (diff != csum_size)
+                if (diff != csum_size) {
                         goto insert;
+                }
+
                 ret = btrfs_extend_item(trans, root, path, diff);
                 BUG_ON(ret);
                 goto csum;
@@ -518,30 +703,3 @@ out:
 fail_unlock:
         goto out;
 }
-
-int btrfs_csum_truncate(struct btrfs_trans_handle *trans,
-                        struct btrfs_root *root, struct btrfs_path *path,
-                        u64 isize)
-{
-        struct btrfs_key key;
-        struct extent_buffer *leaf = path->nodes[0];
-        int slot = path->slots[0];
-        int ret;
-        u32 new_item_size;
-        u64 new_item_span;
-        u64 blocks;
-
-        btrfs_item_key_to_cpu(leaf, &key, slot);
-        if (isize <= key.offset)
-                return 0;
-        new_item_span = isize - key.offset;
-        blocks = (new_item_span + root->sectorsize - 1) >>
-                root->fs_info->sb->s_blocksize_bits;
-        new_item_size = blocks *
-                btrfs_super_csum_size(&root->fs_info->super_copy);
-        if (new_item_size >= btrfs_item_size_nr(leaf, slot))
-                return 0;
-        ret = btrfs_truncate_item(trans, root, path, new_item_size, 1);
-        BUG_ON(ret);
-        return ret;
-}