Re: [PATCH v2 5/6] btrfs-progs: fix-data-checksum: update csum items to fix csum mismatch

[David Sterba <dsterba@suse.cz>]

On Thu, May 15, 2025 at 05:30:20PM +0930, Qu Wenruo wrote:
> +static int update_csum_item(struct btrfs_fs_info *fs_info, u64 logical,
> +			    unsigned int mirror)
> +{
> +	struct btrfs_trans_handle *trans;
> +	struct btrfs_root *csum_root = btrfs_csum_root(fs_info, logical);
> +	struct btrfs_path path = { 0 };
> +	struct btrfs_csum_item *citem;
> +	u64 read_len = fs_info->sectorsize;
> +	u8 csum[BTRFS_CSUM_SIZE] = { 0 };
> +	u8 *buf;
> +	int ret;
> +
> +	buf = malloc(fs_info->sectorsize);
> +	if (!buf)
> +		return -ENOMEM;

Not fixed, but the block buffers can be on stack as well if they're just
for the single function, the size is bounded.

> +	ret = read_data_from_disk(fs_info, buf, logical, &read_len, mirror);
> +	if (ret < 0) {
> +		errno = -ret;
> +		error("failed to read block at logical %llu mirror %u: %m",
> +			logical, mirror);
> +		goto out;
> +	}
> +	trans = btrfs_start_transaction(csum_root, 1);
> +	if (IS_ERR(trans)) {
> +		ret = PTR_ERR(trans);
> +		errno = -ret;
> +		error_msg(ERROR_MSG_START_TRANS, "%m");
> +		goto out;
> +	}
> +	citem = btrfs_lookup_csum(trans, csum_root, &path, logical,
> +				  BTRFS_EXTENT_CSUM_OBJECTID, fs_info->csum_type, 1);
> +	if (IS_ERR(citem)) {
> +		ret = PTR_ERR(citem);
> +		errno = -ret;
> +		error("failed to find csum item for logical %llu: $m", logical);
> +		btrfs_abort_transaction(trans, ret);
> +		goto out;
> +	}
> +	btrfs_csum_data(fs_info, fs_info->csum_type, buf, csum, fs_info->sectorsize);
> +	write_extent_buffer(path.nodes[0], csum, (unsigned long)citem, fs_info->csum_size);
> +	btrfs_release_path(&path);
> +	ret = btrfs_commit_transaction(trans, csum_root);
> +	if (ret < 0) {
> +		errno = -ret;
> +		error_msg(ERROR_MSG_COMMIT_TRANS, "%m");
> +	}
> +	printf("Csum item for logical %llu updated using data from mirror %u\n",
> +		logical, mirror);
> +out:
> +	free(buf);
> +	btrfs_release_path(&path);
> +	return ret;
>  }
>  
>  static void report_corrupted_blocks(struct btrfs_fs_info *fs_info,