Date:   Thu, 14 Sep 2023 18:55:31 +0930
From:   Qu Wenruo <quwenruo.btrfs@....com>
To:     Johannes Thumshirn <johannes.thumshirn@....com>,
        Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>
Cc:     Christoph Hellwig <hch@....de>,
        Naohiro Aota <naohiro.aota@....com>, Qu Wenruo <wqu@...e.com>,
        Damien Le Moal <dlemoal@...nel.org>,
        linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 03/11] btrfs: add support for inserting raid stripe
 extents



On 2023/9/11 22:22, Johannes Thumshirn wrote:
> Add support for inserting stripe extents into the raid stripe tree on
> completion of every write that needs an extra logical-to-physical
> translation when using RAID.
>
> Inserting the stripe extents happens after the data I/O has completed,
> this is done to a) support zone-append and b) rule out the possibility of
> a RAID-write-hole.
>
> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@....com>
> ---
>   fs/btrfs/Makefile           |   2 +-
>   fs/btrfs/bio.c              |  23 ++++
>   fs/btrfs/extent-tree.c      |   1 +
>   fs/btrfs/inode.c            |   8 +-
>   fs/btrfs/ordered-data.c     |   1 +
>   fs/btrfs/ordered-data.h     |   2 +
>   fs/btrfs/raid-stripe-tree.c | 266 ++++++++++++++++++++++++++++++++++++++++++++
>   fs/btrfs/raid-stripe-tree.h |  34 ++++++
>   fs/btrfs/volumes.c          |   4 +-
>   fs/btrfs/volumes.h          |  15 ++-
>   10 files changed, 347 insertions(+), 9 deletions(-)
>
> diff --git a/fs/btrfs/Makefile b/fs/btrfs/Makefile
> index c57d80729d4f..525af975f61c 100644
> --- a/fs/btrfs/Makefile
> +++ b/fs/btrfs/Makefile
> @@ -33,7 +33,7 @@ btrfs-y += super.o ctree.o extent-tree.o print-tree.o root-tree.o dir-item.o \
>   	   uuid-tree.o props.o free-space-tree.o tree-checker.o space-info.o \
>   	   block-rsv.o delalloc-space.o block-group.o discard.o reflink.o \
>   	   subpage.o tree-mod-log.o extent-io-tree.o fs.o messages.o bio.o \
> -	   lru_cache.o
> +	   lru_cache.o raid-stripe-tree.o
>
>   btrfs-$(CONFIG_BTRFS_FS_POSIX_ACL) += acl.o
>   btrfs-$(CONFIG_BTRFS_FS_REF_VERIFY) += ref-verify.o
> diff --git a/fs/btrfs/bio.c b/fs/btrfs/bio.c
> index 31ff36990404..ddbe6f8d4ea2 100644
> --- a/fs/btrfs/bio.c
> +++ b/fs/btrfs/bio.c
> @@ -14,6 +14,7 @@
>   #include "rcu-string.h"
>   #include "zoned.h"
>   #include "file-item.h"
> +#include "raid-stripe-tree.h"
>
>   static struct bio_set btrfs_bioset;
>   static struct bio_set btrfs_clone_bioset;
> @@ -415,6 +416,9 @@ static void btrfs_orig_write_end_io(struct bio *bio)
>   	else
>   		bio->bi_status = BLK_STS_OK;
>
> +	if (bio_op(bio) == REQ_OP_ZONE_APPEND && !bio->bi_status)
> +		stripe->physical = bio->bi_iter.bi_sector << SECTOR_SHIFT;
> +
>   	btrfs_orig_bbio_end_io(bbio);
>   	btrfs_put_bioc(bioc);
>   }
> @@ -426,6 +430,8 @@ static void btrfs_clone_write_end_io(struct bio *bio)
>   	if (bio->bi_status) {
>   		atomic_inc(&stripe->bioc->error);
>   		btrfs_log_dev_io_error(bio, stripe->dev);
> +	} else if (bio_op(bio) == REQ_OP_ZONE_APPEND) {
> +		stripe->physical = bio->bi_iter.bi_sector << SECTOR_SHIFT;
>   	}
>
>   	/* Pass on control to the original bio this one was cloned from */
> @@ -487,6 +493,7 @@ static void btrfs_submit_mirrored_bio(struct btrfs_io_context *bioc, int dev_nr)
>   	bio->bi_private = &bioc->stripes[dev_nr];
>   	bio->bi_iter.bi_sector = bioc->stripes[dev_nr].physical >> SECTOR_SHIFT;
>   	bioc->stripes[dev_nr].bioc = bioc;
> +	bioc->size = bio->bi_iter.bi_size;
>   	btrfs_submit_dev_bio(bioc->stripes[dev_nr].dev, bio);
>   }
>
> @@ -496,6 +503,8 @@ static void __btrfs_submit_bio(struct bio *bio, struct btrfs_io_context *bioc,
>   	if (!bioc) {
>   		/* Single mirror read/write fast path. */
>   		btrfs_bio(bio)->mirror_num = mirror_num;
> +		if (bio_op(bio) != REQ_OP_READ)
> +			btrfs_bio(bio)->orig_physical = smap->physical;
>   		bio->bi_iter.bi_sector = smap->physical >> SECTOR_SHIFT;
>   		if (bio_op(bio) != REQ_OP_READ)
>   			btrfs_bio(bio)->orig_physical = smap->physical;
> @@ -688,6 +697,20 @@ static bool btrfs_submit_chunk(struct btrfs_bio *bbio, int mirror_num)
>   			bio->bi_opf |= REQ_OP_ZONE_APPEND;
>   		}
>
> +		if (is_data_bbio(bbio) && bioc &&
> +		    btrfs_need_stripe_tree_update(bioc->fs_info,
> +						  bioc->map_type)) {
> +			/*
> +			 * No locking for the list update, as we only add to
> +			 * the list in the I/O submission path, and list
> +			 * iteration only happens in the completion path,
> +			 * which can't happen until after the last submission.
> +			 */
> +			btrfs_get_bioc(bioc);
> +			list_add_tail(&bioc->ordered_entry,
> +				      &bbio->ordered->bioc_list);
> +		}
> +
>   		/*
>   		 * Csum items for reloc roots have already been cloned at this
>   		 * point, so they are handled as part of the no-checksum case.
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 6f6838226fe7..2e11a699ab77 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -42,6 +42,7 @@
>   #include "file-item.h"
>   #include "orphan.h"
>   #include "tree-checker.h"
> +#include "raid-stripe-tree.h"
>
>   #undef SCRAMBLE_DELAYED_REFS
>
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index bafca05940d7..6f71630248da 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -71,6 +71,7 @@
>   #include "super.h"
>   #include "orphan.h"
>   #include "backref.h"
> +#include "raid-stripe-tree.h"
>
>   struct btrfs_iget_args {
>   	u64 ino;
> @@ -3091,6 +3092,10 @@ int btrfs_finish_one_ordered(struct btrfs_ordered_extent *ordered_extent)
>
>   	trans->block_rsv = &inode->block_rsv;
>
> +	ret = btrfs_insert_raid_extent(trans, ordered_extent);
> +	if (ret)
> +		goto out;
> +
>   	if (test_bit(BTRFS_ORDERED_COMPRESSED, &ordered_extent->flags))
>   		compress_type = ordered_extent->compress_type;
>   	if (test_bit(BTRFS_ORDERED_PREALLOC, &ordered_extent->flags)) {
> @@ -3224,7 +3229,8 @@ int btrfs_finish_one_ordered(struct btrfs_ordered_extent *ordered_extent)
>   int btrfs_finish_ordered_io(struct btrfs_ordered_extent *ordered)
>   {
>   	if (btrfs_is_zoned(btrfs_sb(ordered->inode->i_sb)) &&
> -	    !test_bit(BTRFS_ORDERED_IOERR, &ordered->flags))
> +	    !test_bit(BTRFS_ORDERED_IOERR, &ordered->flags) &&
> +	    list_empty(&ordered->bioc_list))
>   		btrfs_finish_ordered_zoned(ordered);
>   	return btrfs_finish_one_ordered(ordered);
>   }
> diff --git a/fs/btrfs/ordered-data.c b/fs/btrfs/ordered-data.c
> index 345c449d588c..55c7d5543265 100644
> --- a/fs/btrfs/ordered-data.c
> +++ b/fs/btrfs/ordered-data.c
> @@ -191,6 +191,7 @@ static struct btrfs_ordered_extent *alloc_ordered_extent(
>   	INIT_LIST_HEAD(&entry->log_list);
>   	INIT_LIST_HEAD(&entry->root_extent_list);
>   	INIT_LIST_HEAD(&entry->work_list);
> +	INIT_LIST_HEAD(&entry->bioc_list);
>   	init_completion(&entry->completion);
>
>   	/*
> diff --git a/fs/btrfs/ordered-data.h b/fs/btrfs/ordered-data.h
> index 173bd5c5df26..1c51ac57e5df 100644
> --- a/fs/btrfs/ordered-data.h
> +++ b/fs/btrfs/ordered-data.h
> @@ -151,6 +151,8 @@ struct btrfs_ordered_extent {
>   	struct completion completion;
>   	struct btrfs_work flush_work;
>   	struct list_head work_list;
> +
> +	struct list_head bioc_list;
>   };
>
>   static inline void
> diff --git a/fs/btrfs/raid-stripe-tree.c b/fs/btrfs/raid-stripe-tree.c
> new file mode 100644
> index 000000000000..2415698a8fef
> --- /dev/null
> +++ b/fs/btrfs/raid-stripe-tree.c
> @@ -0,0 +1,266 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2023 Western Digital Corporation or its affiliates.
> + */
> +
> +#include <linux/btrfs_tree.h>
> +
> +#include "ctree.h"
> +#include "fs.h"
> +#include "accessors.h"
> +#include "transaction.h"
> +#include "disk-io.h"
> +#include "raid-stripe-tree.h"
> +#include "volumes.h"
> +#include "misc.h"
> +#include "print-tree.h"
> +
> +static u8 btrfs_bg_type_to_raid_encoding(u64 map_type)
> +{
> +	switch (map_type & BTRFS_BLOCK_GROUP_PROFILE_MASK) {
> +	case BTRFS_BLOCK_GROUP_DUP:
> +		return BTRFS_STRIPE_DUP;
> +	case BTRFS_BLOCK_GROUP_RAID0:
> +		return BTRFS_STRIPE_RAID0;
> +	case BTRFS_BLOCK_GROUP_RAID1:
> +		return BTRFS_STRIPE_RAID1;
> +	case BTRFS_BLOCK_GROUP_RAID1C3:
> +		return BTRFS_STRIPE_RAID1C3;
> +	case BTRFS_BLOCK_GROUP_RAID1C4:
> +		return BTRFS_STRIPE_RAID1C4;
> +	case BTRFS_BLOCK_GROUP_RAID5:
> +		return BTRFS_STRIPE_RAID5;
> +	case BTRFS_BLOCK_GROUP_RAID6:
> +		return BTRFS_STRIPE_RAID6;
> +	case BTRFS_BLOCK_GROUP_RAID10:
> +		return BTRFS_STRIPE_RAID10;
> +	default:
> +		ASSERT(0);
> +	}
> +}
> +
> +static int btrfs_insert_one_raid_extent(struct btrfs_trans_handle *trans,
> +				 int num_stripes,
> +				 struct btrfs_io_context *bioc)
> +{
> +	struct btrfs_fs_info *fs_info = trans->fs_info;
> +	struct btrfs_key stripe_key;
> +	struct btrfs_root *stripe_root = btrfs_stripe_tree_root(fs_info);
> +	u8 encoding = btrfs_bg_type_to_raid_encoding(bioc->map_type);
> +	struct btrfs_stripe_extent *stripe_extent;
> +	size_t item_size;
> +	int ret;
> +
> +	item_size = struct_size(stripe_extent, strides, num_stripes);

I guess David has already pointed out this can be done at initialization
and make it const.

> +
> +	stripe_extent = kzalloc(item_size, GFP_NOFS);
> +	if (!stripe_extent) {
> +		btrfs_abort_transaction(trans, -ENOMEM);
> +		btrfs_end_transaction(trans);
> +		return -ENOMEM;
> +	}
> +
> +	btrfs_set_stack_stripe_extent_encoding(stripe_extent, encoding);
> +	for (int i = 0; i < num_stripes; i++) {
> +		u64 devid = bioc->stripes[i].dev->devid;
> +		u64 physical = bioc->stripes[i].physical;
> +		u64 length = bioc->stripes[i].length;
> +		struct btrfs_raid_stride *raid_stride =
> +						&stripe_extent->strides[i];
> +
> +		if (length == 0)
> +			length = bioc->size;
> +
> +		btrfs_set_stack_raid_stride_devid(raid_stride, devid);
> +		btrfs_set_stack_raid_stride_physical(raid_stride, physical);
> +		btrfs_set_stack_raid_stride_length(raid_stride, length);
> +	}
> +
> +	stripe_key.objectid = bioc->logical;
> +	stripe_key.type = BTRFS_RAID_STRIPE_KEY;
> +	stripe_key.offset = bioc->size;
> +
> +	ret = btrfs_insert_item(trans, stripe_root, &stripe_key, stripe_extent,
> +				item_size);

Have you tested in near-real-world on how continous the RST items could
be for RAID0/RAID10?

My concern here is, we may want to try our best to reduce the size of
RST, due to the 64K BTRFS_STRIPE_LEN.


> +	if (ret)
> +		btrfs_abort_transaction(trans, ret);
> +
> +	kfree(stripe_extent);
> +
> +	return ret;
> +}
> +
> +static int btrfs_insert_mirrored_raid_extents(struct btrfs_trans_handle *trans,
> +				      struct btrfs_ordered_extent *ordered,
> +				      u64 map_type)
> +{
> +	int num_stripes = btrfs_bg_type_to_factor(map_type);
> +	struct btrfs_io_context *bioc;
> +	int ret;
> +
> +	list_for_each_entry(bioc, &ordered->bioc_list, ordered_entry) {
> +		ret = btrfs_insert_one_raid_extent(trans, num_stripes, bioc);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +static int btrfs_insert_striped_mirrored_raid_extents(
> +				      struct btrfs_trans_handle *trans,
> +				      struct btrfs_ordered_extent *ordered,
> +				      u64 map_type)
> +{
> +	struct btrfs_io_context *bioc;
> +	struct btrfs_io_context *rbioc;
> +	const int nstripes = list_count_nodes(&ordered->bioc_list);
> +	const int index = btrfs_bg_flags_to_raid_index(map_type);
> +	const int substripes = btrfs_raid_array[index].sub_stripes;
> +	const int max_stripes = trans->fs_info->fs_devices->rw_devices / 2;
> +	int left = nstripes;
> +	int stripe = 0, j = 0;
> +	int i = 0;
> +	int ret = 0;
> +	u64 stripe_end;
> +	u64 prev_end;
> +
> +	if (nstripes == 1)
> +		return btrfs_insert_mirrored_raid_extents(trans, ordered, map_type);
> +
> +	rbioc = kzalloc(struct_size(rbioc, stripes, nstripes * substripes),
> +			GFP_KERNEL);
> +	if (!rbioc)
> +		return -ENOMEM;
> +
> +	rbioc->map_type = map_type;
> +	rbioc->logical = list_first_entry(&ordered->bioc_list, typeof(*rbioc),
> +					   ordered_entry)->logical;
> +
> +	stripe_end = rbioc->logical;
> +	prev_end = stripe_end;
> +	list_for_each_entry(bioc, &ordered->bioc_list, ordered_entry) {
> +
> +		rbioc->size += bioc->size;
> +		for (j = 0; j < substripes; j++) {
> +			stripe = i + j;
> +			rbioc->stripes[stripe].dev = bioc->stripes[j].dev;
> +			rbioc->stripes[stripe].physical = bioc->stripes[j].physical;
> +			rbioc->stripes[stripe].length = bioc->size;
> +		}
> +
> +		stripe_end += rbioc->size;
> +		if (i >= nstripes ||
> +		    (stripe_end - prev_end >= max_stripes * BTRFS_STRIPE_LEN)) {
> +			ret = btrfs_insert_one_raid_extent(trans,
> +							   nstripes * substripes,
> +							   rbioc);
> +			if (ret)
> +				goto out;
> +
> +			left -= nstripes;
> +			i = 0;
> +			rbioc->logical += rbioc->size;
> +			rbioc->size = 0;
> +		} else {
> +			i += substripes;
> +			prev_end = stripe_end;
> +		}
> +	}
> +
> +	if (left) {
> +		bioc = list_prev_entry(bioc, ordered_entry);
> +		ret = btrfs_insert_one_raid_extent(trans, substripes, bioc);
> +	}
> +
> +out:
> +	kfree(rbioc);
> +	return ret;
> +}
> +
> +static int btrfs_insert_striped_raid_extents(struct btrfs_trans_handle *trans,
> +				     struct btrfs_ordered_extent *ordered,
> +				     u64 map_type)
> +{
> +	struct btrfs_io_context *bioc;
> +	struct btrfs_io_context *rbioc;
> +	const int nstripes = list_count_nodes(&ordered->bioc_list);
> +	int i = 0;
> +	int ret = 0;
> +
> +	rbioc = kzalloc(struct_size(rbioc, stripes, nstripes), GFP_KERNEL);
> +	if (!rbioc)
> +		return -ENOMEM;
> +	rbioc->map_type = map_type;
> +	rbioc->logical = list_first_entry(&ordered->bioc_list, typeof(*rbioc),
> +					   ordered_entry)->logical;
> +
> +	list_for_each_entry(bioc, &ordered->bioc_list, ordered_entry) {
> +		rbioc->size += bioc->size;
> +		rbioc->stripes[i].dev = bioc->stripes[0].dev;
> +		rbioc->stripes[i].physical = bioc->stripes[0].physical;
> +		rbioc->stripes[i].length = bioc->size;
> +
> +		if (i == nstripes - 1) {
> +			ret = btrfs_insert_one_raid_extent(trans, nstripes, rbioc);
> +			if (ret)
> +				goto out;
> +
> +			i = 0;
> +			rbioc->logical += rbioc->size;
> +			rbioc->size = 0;
> +		} else {
> +			i++;
> +		}
> +	}
> +
> +	if (i && i < nstripes - 1)
> +		ret = btrfs_insert_one_raid_extent(trans, i, rbioc);
> +
> +out:
> +	kfree(rbioc);
> +	return ret;
> +}
> +
> +int btrfs_insert_raid_extent(struct btrfs_trans_handle *trans,
> +			     struct btrfs_ordered_extent *ordered_extent)
> +{
> +	struct btrfs_io_context *bioc;
> +	u64 map_type;
> +	int ret;
> +
> +	if (!trans->fs_info->stripe_root)
> +		return 0;
> +
> +	map_type = list_first_entry(&ordered_extent->bioc_list, typeof(*bioc),
> +				    ordered_entry)->map_type;
> +
> +	switch (map_type & BTRFS_BLOCK_GROUP_PROFILE_MASK) {
> +	case BTRFS_BLOCK_GROUP_DUP:
> +	case BTRFS_BLOCK_GROUP_RAID1:
> +	case BTRFS_BLOCK_GROUP_RAID1C3:
> +	case BTRFS_BLOCK_GROUP_RAID1C4:
> +		ret = btrfs_insert_mirrored_raid_extents(trans, ordered_extent,
> +							 map_type);
> +		break;
> +	case BTRFS_BLOCK_GROUP_RAID0:
> +		ret = btrfs_insert_striped_raid_extents(trans, ordered_extent,
> +							map_type);
> +		break;
> +	case BTRFS_BLOCK_GROUP_RAID10:
> +		ret = btrfs_insert_striped_mirrored_raid_extents(trans, ordered_extent, map_type);
> +		break;
> +	default:
> +		ret = -EINVAL;

Maybe we want to be a little more noisy?

Thanks,
Qu

> +		break;
> +	}
> +
> +	while (!list_empty(&ordered_extent->bioc_list)) {
> +		bioc = list_first_entry(&ordered_extent->bioc_list,
> +					typeof(*bioc), ordered_entry);
> +		list_del(&bioc->ordered_entry);
> +		btrfs_put_bioc(bioc);
> +	}
> +
> +	return ret;
> +}
> diff --git a/fs/btrfs/raid-stripe-tree.h b/fs/btrfs/raid-stripe-tree.h
> new file mode 100644
> index 000000000000..f36e4c2d46b0
> --- /dev/null
> +++ b/fs/btrfs/raid-stripe-tree.h
> @@ -0,0 +1,34 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (C) 2023 Western Digital Corporation or its affiliates.
> + */
> +
> +#ifndef BTRFS_RAID_STRIPE_TREE_H
> +#define BTRFS_RAID_STRIPE_TREE_H
> +
> +#include "disk-io.h"
> +
> +struct btrfs_io_context;
> +struct btrfs_io_stripe;
> +
> +int btrfs_insert_raid_extent(struct btrfs_trans_handle *trans,
> +			     struct btrfs_ordered_extent *ordered_extent);
> +
> +static inline bool btrfs_need_stripe_tree_update(struct btrfs_fs_info *fs_info,
> +						 u64 map_type)
> +{
> +	u64 type = map_type & BTRFS_BLOCK_GROUP_TYPE_MASK;
> +	u64 profile = map_type & BTRFS_BLOCK_GROUP_PROFILE_MASK;
> +
> +	if (!btrfs_stripe_tree_root(fs_info))
> +		return false;
> +
> +	if (type != BTRFS_BLOCK_GROUP_DATA)
> +		return false;
> +
> +	if (profile & BTRFS_BLOCK_GROUP_RAID1_MASK)
> +		return true;
> +
> +	return false;
> +}
> +#endif
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 871a55d36e32..0c0fd4eb4848 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -5881,6 +5881,7 @@ static int find_live_mirror(struct btrfs_fs_info *fs_info,
>   }
>
>   static struct btrfs_io_context *alloc_btrfs_io_context(struct btrfs_fs_info *fs_info,
> +						       u64 logical,
>   						       u16 total_stripes)
>   {
>   	struct btrfs_io_context *bioc;
> @@ -5900,6 +5901,7 @@ static struct btrfs_io_context *alloc_btrfs_io_context(struct btrfs_fs_info *fs_
>   	bioc->fs_info = fs_info;
>   	bioc->replace_stripe_src = -1;
>   	bioc->full_stripe_logical = (u64)-1;
> +	bioc->logical = logical;
>
>   	return bioc;
>   }
> @@ -6434,7 +6436,7 @@ int btrfs_map_block(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
>   		goto out;
>   	}
>
> -	bioc = alloc_btrfs_io_context(fs_info, num_alloc_stripes);
> +	bioc = alloc_btrfs_io_context(fs_info, logical, num_alloc_stripes);
>   	if (!bioc) {
>   		ret = -ENOMEM;
>   		goto out;
> diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
> index 576bfcb5b764..8604bfbbf510 100644
> --- a/fs/btrfs/volumes.h
> +++ b/fs/btrfs/volumes.h
> @@ -390,12 +390,11 @@ struct btrfs_fs_devices {
>
>   struct btrfs_io_stripe {
>   	struct btrfs_device *dev;
> -	union {
> -		/* Block mapping */
> -		u64 physical;
> -		/* For the endio handler */
> -		struct btrfs_io_context *bioc;
> -	};
> +	/* Block mapping */
> +	u64 physical;
> +	u64 length;
> +	/* For the endio handler */
> +	struct btrfs_io_context *bioc;
>   };
>
>   struct btrfs_discard_stripe {
> @@ -428,6 +427,10 @@ struct btrfs_io_context {
>   	atomic_t error;
>   	u16 max_errors;
>
> +	u64 logical;
> +	u64 size;
> +	struct list_head ordered_entry;
> +
>   	/*
>   	 * The total number of stripes, including the extra duplicated
>   	 * stripe for replace.
>

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