btrfs-progs: corrupt-block: Refactor tree block corruption code

As progs' transaction/CoW logic evolved over the years the metadata block
corruption code failed to do so. It's currently impossible to corrupt
the generation because the CoW logic will not only set it to the value
of the currently running transaction (__btrfs_cow_block) but the
current code will ASSERT due to the following check in __btrfs_cow_block:

   WARN_ON(!(buf->flags & EXTENT_BAD_TRANSID) &&
                   btrfs_header_generation(buf) > trans->transid);

Fix this by making the generation corruption code directly write
the modified block, outside of the transaction mechanism. At the same
time move the old code into BTRFS_METADATA_BLOCK_SHIFT_ITEMS handling
case, essentially leaving it unchanged.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

btrfs-corrupt-block.c

@@ -747,15 +747,8 @@ static void shift_items(struct btrfs_root *root, struct extent_buffer *eb)
 static int corrupt_metadata_block(struct btrfs_fs_info *fs_info, u64 block,
 				  char *field)
 {
-	struct btrfs_trans_handle *trans;
-	struct btrfs_root *root;
-	struct btrfs_path *path;
 	struct extent_buffer *eb;
-	struct btrfs_key key, root_key;
 	enum btrfs_metadata_block_field corrupt_field;
-	u64 root_objectid;
-	u64 orig, bogus;
-	u8 level;
 	int ret;
 
 	corrupt_field = convert_metadata_block_field(field);
@@ -769,63 +762,78 @@ static int corrupt_metadata_block(struct btrfs_fs_info *fs_info, u64 block,
 		fprintf(stderr, "Couldn't read in tree block %s\n", field);
 		return -EINVAL;
 	}
-	root_objectid = btrfs_header_owner(eb);
-	level = btrfs_header_level(eb);
-	if (level)
-		btrfs_node_key_to_cpu(eb, &key, 0);
-	else
-		btrfs_item_key_to_cpu(eb, &key, 0);
-	free_extent_buffer(eb);
-
-	root_key.objectid = root_objectid;
-	root_key.type = BTRFS_ROOT_ITEM_KEY;
-	root_key.offset = (u64)-1;
-
-	root = btrfs_read_fs_root(fs_info, &root_key);
-	if (IS_ERR(root)) {
-		fprintf(stderr, "Couldn't find owner root %llu\n",
-			key.objectid);
-		return PTR_ERR(root);
-	}
-
-	path = btrfs_alloc_path();
-	if (!path)
-		return -ENOMEM;
-
-	trans = btrfs_start_transaction(root, 1);
-	if (IS_ERR(trans)) {
-		btrfs_free_path(path);
-		fprintf(stderr, "Couldn't start transaction %ld\n",
-			PTR_ERR(trans));
-		return PTR_ERR(trans);
-	}
-
-	path->lowest_level = level;
-	ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
-	if (ret < 0) {
-		fprintf(stderr, "Error searching to node %d\n", ret);
-		goto out;
-	}
-	eb = path->nodes[level];
 
 	ret = 0;
 	switch (corrupt_field) {
 	case BTRFS_METADATA_BLOCK_GENERATION:
-		orig = btrfs_header_generation(eb);
-		bogus = generate_u64(orig);
+		{
+		u64 orig = btrfs_header_generation(eb);
+		u64 bogus = generate_u64(orig);
+
 		btrfs_set_header_generation(eb, bogus);
+		write_and_map_eb(fs_info, eb);
+		free_extent_buffer(eb);
 		break;
+		}
 	case BTRFS_METADATA_BLOCK_SHIFT_ITEMS:
+		{
+		struct btrfs_trans_handle *trans;
+		struct btrfs_root *root;
+		struct btrfs_path *path;
+		struct btrfs_key key, root_key;
+		u64 root_objectid;
+		u8 level;
+
+		root_objectid = btrfs_header_owner(eb);
+		level = btrfs_header_level(eb);
+		if (level)
+			btrfs_node_key_to_cpu(eb, &key, 0);
+		else
+			btrfs_item_key_to_cpu(eb, &key, 0);
+		free_extent_buffer(eb);
+
+		root_key.objectid = root_objectid;
+		root_key.type = BTRFS_ROOT_ITEM_KEY;
+		root_key.offset = (u64)-1;
+
+		root = btrfs_read_fs_root(fs_info, &root_key);
+		if (IS_ERR(root)) {
+			fprintf(stderr, "Couldn't find owner root %llu\n",
+				key.objectid);
+			return PTR_ERR(root);
+		}
+
+		path = btrfs_alloc_path();
+		if (!path)
+			return -ENOMEM;
+
+		trans = btrfs_start_transaction(root, 1);
+		if (IS_ERR(trans)) {
+			btrfs_free_path(path);
+			fprintf(stderr, "Couldn't start transaction %ld\n",
+				PTR_ERR(trans));
+			return PTR_ERR(trans);
+		}
+
+		path->lowest_level = level;
+		ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
+		if (ret < 0) {
+			fprintf(stderr, "Error searching to node %d\n", ret);
+			btrfs_free_path(path);
+			btrfs_abort_transaction(trans, ret);
+			return ret;
+		}
+		eb = path->nodes[level];
 		shift_items(root, path->nodes[level]);
+		btrfs_mark_buffer_dirty(path->nodes[level]);
+		btrfs_commit_transaction(trans, root);
 		break;
+		}
 	default:
 		ret = -EINVAL;
 		break;
 	}
-	btrfs_mark_buffer_dirty(path->nodes[level]);
-out:
-	btrfs_commit_transaction(trans, root);
-	btrfs_free_path(path);
+
 	return ret;
 }