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

[Qu Wenruo <wqu@suse.com>]

在 2025/5/30 20:49, David Sterba 写道:
> 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.

Unfortunately the sectorsize is still runtime determined, thus it can 
not be on-stack.

Thanks,
Qu>
>> +	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,