Re: [PATCH 1/4] btrfs-progs: Introduce functions to repair unaligned/mismatch device size

[Nikolay Borisov <nborisov@suse.com>]

On 10.10.2017 10:51, Qu Wenruo wrote:
> This patch introduces functions to repair device size related problems,
> including:
> 1) Unaligned total_bytes of dev_item
>    v4.14-rc kernel introduced total_bytes alignment checker.
>    However older kernel device add/shrink doesn't align these members.
>    This will cause kernel warning every time dev_item get updated.
> 
>    Although it can be fixed by shrinking device on latest kernel or
>    use manually aligned size on older kernel, a fallback method in
>    btrfs-progs won't hurt.
> 
> 2) Mismatch super->total_bytes
>    There are some reports about unmountable fs, due to mismatched
>    super->total_bytes.
>    And normal kernel device shrink won't help since it only modify the
>    total_bytes by the size changed, not re-calculating it.
> 
>    The root cause is still under investigation, but at least to fix it
>    in btrfs-progs
> 
> Fix all of them by manually rounding down total_bytes of each device, and
> recalculate super->total_bytes using all existing devices.

Thanks for doing this, we needed it. One minor nit in the comments but
overall:

Reviewed-by: Nikolay Borisov <nborisov@suse.com>


> 
> Reported-by: Asif Youssuff <yoasif@gmail.com>
> Reported-by: Rich Rauenzahn <rrauenza@gmail.com>
> Signed-off-by: Qu Wenruo <quwenruo.btrfs@gmx.com>> ---
>  cmds-check.c | 191 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 191 insertions(+)
> 
> diff --git a/cmds-check.c b/cmds-check.c
> index 0c08618ed701..007781fa5d1b 100644
> --- a/cmds-check.c
> +++ b/cmds-check.c
> @@ -12885,6 +12885,197 @@ close_out:
>  	return ret;
>  }
>  
> +/*
> + * Return 0 if DEV_ITEM for @device is good
> + * Return >0 if DEV_ITEM for @device has unaligned value and fixed
> + * Return <0 if we failed to fix the unaligned value
> + */
> +static int reset_one_dev_size(struct btrfs_fs_info *fs_info,
> +			       struct btrfs_device *device)
> +{
> +	struct btrfs_trans_handle *trans;
> +	struct btrfs_key key;
> +	struct btrfs_path path;
> +	struct btrfs_root *chunk_root = fs_info->chunk_root;
> +	struct btrfs_dev_item *di;
> +	u64 old_bytes = device->total_bytes;
> +	int ret;
> +
> +	if (IS_ALIGNED(device->total_bytes, fs_info->sectorsize))
> +		return 0;
> +
> +	/* Align the in-memory total_bytes first, and use it later */
> +	device->total_bytes = round_down(device->total_bytes,
> +					 fs_info->sectorsize);
> +
> +	key.objectid = BTRFS_DEV_ITEMS_OBJECTID;
> +	key.type = BTRFS_DEV_ITEM_KEY;
> +	key.offset = device->devid;
> +
> +	trans = btrfs_start_transaction(chunk_root, 1);
> +	if (IS_ERR(trans)) {
> +		ret = PTR_ERR(trans);
> +		error("error starting transaction:  %d (%s)",
> +		      ret, strerror(-ret));
> +		return ret;
> +	}
> +
> +	btrfs_init_path(&path);
> +	ret = btrfs_search_slot(trans, chunk_root, &key, &path, 0, 1);
> +	if (ret > 0) {
> +		error("failed to find DEV_ITEM for devid %llu",
> +			device->devid);
> +		ret = -ENOENT;
> +		goto err;
> +	}
> +	if (ret < 0) {
> +		error("failed to search chunk root: %d (%s)",
> +			ret, strerror(-ret));
> +		goto err;
> +	}
> +	di = btrfs_item_ptr(path.nodes[0], path.slots[0],
> +			    struct btrfs_dev_item);
> +	btrfs_set_device_total_bytes(path.nodes[0], di, device->total_bytes);
> +	btrfs_mark_buffer_dirty(path.nodes[0]);
> +	ret = btrfs_commit_transaction(trans, chunk_root);
> +	if (ret < 0) {
> +		error("failed to commit current transaction: %d (%s)",
> +			ret, strerror(-ret));
> +		btrfs_release_path(&path);
> +		return ret;
> +	}
> +	btrfs_release_path(&path);
> +	printf("Fixed device size for devid %llu, old size: %llu new size: %llu\n",
> +		device->devid, old_bytes, device->total_bytes);
> +	return 1;
> +
> +err:
> +	/* We haven't modified anything, it's OK to commit current trans */
> +	btrfs_commit_transaction(trans, chunk_root);
> +	btrfs_release_path(&path);
> +	return ret;
> +}
> +
> +/*
> + * Return 0 if super block total bytes matches with device total_bytes
> + * Return >0 if super block has mismatch total_bytes and fixed
> + * Return <0 if we failed to fix the mismatch total_bytes
> + */
> +static int reset_super_total_bytes(struct btrfs_fs_info *fs_info)
> +{
> +	struct btrfs_trans_handle *trans;
> +	struct btrfs_device *device;
> +	struct list_head *dev_list = &fs_info->fs_devices->devices;
> +	u64 total_bytes = 0;
> +	u64 old_bytes = btrfs_super_total_bytes(fs_info->super_copy);
> +	int ret;
> +
> +	list_for_each_entry(device, dev_list, dev_list)
> +		total_bytes += device->total_bytes;
> +
> +	if (total_bytes == old_bytes)
> +		return 0;
> +
> +	/* Just in case */
> +	if (!IS_ALIGNED(total_bytes, fs_info->sectorsize)) {
> +		error("final total_bytes still not aligned to %u, please report a bug to btrfs mail list",
> +			fs_info->sectorsize);
> +		return -EUCLEAN;
> +	}
> +
> +	btrfs_set_super_total_bytes(fs_info->super_copy, total_bytes);
> +
> +	/* Commit transaction to update all super blocks */
> +	trans = btrfs_start_transaction(fs_info->tree_root, 1);
> +	if (IS_ERR(trans)) {
> +		ret = PTR_ERR(trans);
> +		error("error starting transaction:  %d (%s)",
> +		      ret, strerror(-ret));
> +		return ret;
> +	}
> +	ret = btrfs_commit_transaction(trans, fs_info->tree_root);
> +	if (ret < 0) {
> +		error("failed to commit current transaction: %d (%s)",
> +			ret, strerror(-ret));
> +		return ret;
> +	}
> +	printf("Fixed super total bytes, old size: %llu new size: %llu\n",
> +		old_bytes, total_bytes);
> +	return 1;
> +}
> +
> +/*
> + * Repair device size related problems, including:
> + * 1) Unaligned total_bytes of dev_item
> + *    v4.14-rc kernel introduced total_bytes alignment checker.
> + *    However older kernel device add/shrink doesn't restrictly align
> + *    these members.
> + *    This will cause kernel warning everytime dev_item get updated.
> + *
> + *    Although it can be fixed by shrinking device on latest kernel or
> + *    use manually aligned size on older kernel, a fallback method in
> + *    btrfs-progs won't hurt.
> + *
> + * 2) Mismatch super->total_bytes
> + *    Due to similar situation, super->total_bytes can be mismatch with
> + *    total size of all devices.
> + *    This will cause the filesystem unable to be mounted with v4.14-rc kernel.

The commit which introduced the code preventing mounting can be traced
back to 4.7: 99e3ecfcb9f4 ("Btrfs: add more validation checks for
superblock"). I'd say remove the version information or fix it to point
to v4.7.

> + *
> + *    Add such fixer in btrfs-progs as a fallback method.
> + *
> + * Fix all of them by manually rounding down total_bytes of each device, and
> + * recalculate super->total_bytes using all existing devices.
> + */
> +static int reset_devs_size(struct btrfs_fs_info *fs_info)
> +{
> +	struct btrfs_device *device;
> +	struct list_head *dev_list = &fs_info->fs_devices->devices;
> +	bool have_bad_value = false;
> +	int ret;
> +
> +	/* Seed device is not support yet */
> +	if (fs_info->fs_devices->seed) {
> +		error("resetting device size with seed device is not supported yet");
> +		return -ENOTTY;
> +	}
> +
> +	/* All devices must be on-line before reparing */
> +	if (list_empty(dev_list)) {
> +		error("no device found");
> +		return -ENODEV;
> +	}
> +	list_for_each_entry(device, dev_list, dev_list) {
> +		if (device->fd == -1 || !device->writeable) {
> +			error("device with devid %llu is missing or not writeable",
> +			      device->devid);
> +			error("resetting device size needs all device(s) present and writeable");
> +			return -ENODEV;
> +		}
> +	}
> +
> +	/* Repair total_bytes of each device */
> +	list_for_each_entry(device, dev_list, dev_list) {
> +		ret = reset_one_dev_size(fs_info, device);
> +		if (ret < 0)
> +			return ret;
> +		if (ret > 0)
> +			have_bad_value = true;
> +	}
> +
> +	/* Repair super total_byte */
> +	ret = reset_super_total_bytes(fs_info);
> +	if (ret > 0)
> +		have_bad_value = true;
> +	if (have_bad_value) {
> +		printf("Fixed unaligned/mismatch total_bytes for superblock and device item\n");
> +		ret = 1;
> +	} else {
> +		printf("No device size related problem found\n");
> +		ret = 0;
> +	}
> +	return ret;
> +}
> +
>  const char * const cmd_check_usage[] = {
>  	"btrfs check [options] <device>",
>  	"Check structural integrity of a filesystem (unmounted).",
>