Re: [PATCH] Btrfs-progs: fsck: add an option to check data csums

[Konstantinos Skarlatos <k.skarlatos@gmail.com>]

On 8/5/2014 4:26 πμ, Wang Shilong wrote:
> This patch adds an option '--check-data-csum' to verify data csums.
> fsck won't check data csums unless users specify this option explictly.
Can this option be added to btrfs restore as well? i think it would be a 
good thing if users can tell restore to only recover non-corrupt files.
>
> Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
> ---
>   Documentation/btrfs-check.txt |   2 +
>   cmds-check.c                  | 122 ++++++++++++++++++++++++++++++++++++++++--
>   2 files changed, 120 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/btrfs-check.txt b/Documentation/btrfs-check.txt
> index 485a49c..bc10755 100644
> --- a/Documentation/btrfs-check.txt
> +++ b/Documentation/btrfs-check.txt
> @@ -30,6 +30,8 @@ try to repair the filesystem.
>   create a new CRC tree.
>   --init-extent-tree::
>   create a new extent tree.
> +--check-data-csum::
> +check data csums.
>   
>   EXIT STATUS
>   -----------
> diff --git a/cmds-check.c b/cmds-check.c
> index 103efc5..b53d49c 100644
> --- a/cmds-check.c
> +++ b/cmds-check.c
> @@ -53,6 +53,7 @@ static LIST_HEAD(delete_items);
>   static int repair = 0;
>   static int no_holes = 0;
>   static int init_extent_tree = 0;
> +static int check_data_csum = 0;
>   
>   struct extent_backref {
>   	struct list_head list;
> @@ -3634,6 +3635,106 @@ static int check_space_cache(struct btrfs_root *root)
>   	return error ? -EINVAL : 0;
>   }
>   
> +static int read_extent_data(struct btrfs_root *root, char *data,
> +			u64 logical, u64 len, int mirror)
> +{
> +	u64 offset = 0;
> +	struct btrfs_multi_bio *multi = NULL;
> +	struct btrfs_fs_info *info = root->fs_info;
> +	struct btrfs_device *device;
> +	int ret = 0;
> +	u64 read_len;
> +	unsigned long bytes_left = len;
> +
> +	while (bytes_left) {
> +		read_len = bytes_left;
> +		device = NULL;
> +		ret = btrfs_map_block(&info->mapping_tree, READ,
> +				logical + offset, &read_len, &multi,
> +				mirror, NULL);
> +		if (ret) {
> +			fprintf(stderr, "Couldn't map the block %llu\n",
> +					logical + offset);
> +			goto error;
> +		}
> +		device = multi->stripes[0].dev;
> +
> +		if (device->fd == 0)
> +			goto error;
> +
> +		if (read_len > root->sectorsize)
> +			read_len = root->sectorsize;
> +		if (read_len > bytes_left)
> +			read_len = bytes_left;
> +
> +		ret = pread64(device->fd, data + offset, read_len,
> +			      multi->stripes[0].physical);
> +		if (ret != read_len)
> +			goto error;
> +		offset += read_len;
> +		bytes_left -= read_len;
> +		kfree(multi);
> +		multi = NULL;
> +	}
> +	return 0;
> +error:
> +	kfree(multi);
> +	return -EIO;
> +}
> +
> +static int check_extent_csums(struct btrfs_root *root, u64 bytenr,
> +			u64 num_bytes, unsigned long leaf_offset,
> +			struct extent_buffer *eb) {
> +
> +	u64 offset = 0;
> +	u16 csum_size = btrfs_super_csum_size(root->fs_info->super_copy);
> +	char *data;
> +	u32 crc;
> +	unsigned long tmp;
> +	char result[csum_size];
> +	char out[csum_size];
> +	int ret = 0;
> +	__s64 cmp;
> +	int mirror;
> +	int num_copies = btrfs_num_copies(&root->fs_info->mapping_tree,
> +				bytenr, num_bytes);
> +
> +	BUG_ON(num_bytes % root->sectorsize);
> +	data = malloc(root->sectorsize);
> +	if (!data)
> +		return -ENOMEM;
> +
> +	while (offset < num_bytes) {
> +		mirror = 0;
> +again:
> +		ret = read_extent_data(root, data, bytenr + offset,
> +				root->sectorsize, mirror);
> +		if (ret)
> +			goto out;
> +
> +		crc = ~(u32)0;
> +		crc = btrfs_csum_data(NULL, (char *)data, crc,
> +				      root->sectorsize);
> +		btrfs_csum_final(crc, result);
> +
> +		tmp = leaf_offset + offset / root->sectorsize * csum_size;
> +		read_extent_buffer(eb, out, tmp, csum_size);
> +		cmp = memcmp(out, result, csum_size);
> +		if (cmp) {
> +			fprintf(stderr, "mirror: %d range bytenr: %llu, len: %d checksum mismatch\n",
> +				mirror, bytenr + offset, root->sectorsize);
> +			if (mirror < num_copies - 1) {
> +				mirror += 1;
> +				goto again;
> +			}
> +		}
> +		offset += root->sectorsize;
> +	}
> +out:
> +	free(data);
> +	return ret;
> +}
> +
>   static int check_extent_exists(struct btrfs_root *root, u64 bytenr,
>   			       u64 num_bytes)
>   {
> @@ -3771,6 +3872,8 @@ static int check_csums(struct btrfs_root *root)
>   	u16 csum_size = btrfs_super_csum_size(root->fs_info->super_copy);
>   	int errors = 0;
>   	int ret;
> +	u64 data_len;
> +	unsigned long leaf_offset;
>   
>   	root = root->fs_info->csum_root;
>   
> @@ -3812,6 +3915,16 @@ static int check_csums(struct btrfs_root *root)
>   			continue;
>   		}
>   
> +		data_len = (btrfs_item_size_nr(leaf, path->slots[0]) /
> +			      csum_size) * root->sectorsize;
> +		if (!check_data_csum)
> +			goto skip_csum_check;
> +		leaf_offset = btrfs_item_ptr_offset(leaf, path->slots[0]);
> +		ret = check_extent_csums(root, key.offset, data_len,
> +					 leaf_offset, leaf);
> +		if (ret)
> +			break;
> +skip_csum_check:
>   		if (!num_bytes) {
>   			offset = key.offset;
>   		} else if (key.offset != offset + num_bytes) {
> @@ -3825,9 +3938,7 @@ static int check_csums(struct btrfs_root *root)
>   			offset = key.offset;
>   			num_bytes = 0;
>   		}
> -
> -		num_bytes += (btrfs_item_size_nr(leaf, path->slots[0]) /
> -			      csum_size) * root->sectorsize;
> +		num_bytes += data_len;
>   		path->slots[0]++;
>   	}
>   
> @@ -6665,6 +6776,7 @@ static struct option long_options[] = {
>   	{ "repair", 0, NULL, 0 },
>   	{ "init-csum-tree", 0, NULL, 0 },
>   	{ "init-extent-tree", 0, NULL, 0 },
> +	{ "check-data-csum", 0, NULL, 0 },
>   	{ "backup", 0, NULL, 0 },
>   	{ NULL, 0, NULL, 0}
>   };
> @@ -6678,6 +6790,7 @@ const char * const cmd_check_usage[] = {
>   	"--repair                    try to repair the filesystem",
>   	"--init-csum-tree            create a new CRC tree",
>   	"--init-extent-tree          create a new extent tree",
> +	"--check-data-csum           check data csums",
>   	NULL
>   };
>   
> @@ -6736,8 +6849,9 @@ int cmd_check(int argc, char **argv)
>   			ctree_flags |= (OPEN_CTREE_WRITES |
>   					OPEN_CTREE_NO_BLOCK_GROUPS);
>   			repair = 1;
> +		} else if (option_index == 4) {
> +			check_data_csum = 1;
>   		}
> -
>   	}
>   	argc = argc - optind;
>