Re: [PATCH v4 1/7] btrfs: replace stripe extents

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

在 2024/7/6 00:43, Johannes Thumshirn 写道:
> From: Johannes Thumshirn <johannes.thumshirn@wdc.com>
>
> If we can't insert a stripe extent in the RAID stripe tree, because
> the key that points to the specific position in the stripe tree is
> already existing, we have to remove the item and then replace it by a
> new item.
>
> This can happen for example on device replace operations.

In that case, can we just modify the targeted dev stripe?

Or do we have other call sites that can lead to such conflicts?

As I'm not that confident if such replace behavior would mask some real
problems.

Thanks,
Qu

>
> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> ---
>   fs/btrfs/raid-stripe-tree.c | 36 ++++++++++++++++++++++++++++++++++++
>   1 file changed, 36 insertions(+)
>
> diff --git a/fs/btrfs/raid-stripe-tree.c b/fs/btrfs/raid-stripe-tree.c
> index e6f7a234b8f6..3b32e96c33fc 100644
> --- a/fs/btrfs/raid-stripe-tree.c
> +++ b/fs/btrfs/raid-stripe-tree.c
> @@ -73,6 +73,39 @@ int btrfs_delete_raid_extent(struct btrfs_trans_handle *trans, u64 start, u64 le
>   	return ret;
>   }
>
> +static int replace_raid_extent_item(struct btrfs_trans_handle *trans,
> +				    struct btrfs_key *key,
> +				    struct btrfs_stripe_extent *stripe_extent,
> +				    const size_t item_size)
> +{
> +	struct btrfs_fs_info *fs_info = trans->fs_info;
> +	struct btrfs_root *stripe_root = fs_info->stripe_root;
> +	struct btrfs_path *path;
> +	int ret;
> +
> +	path = btrfs_alloc_path();
> +	if (!path)
> +		return -ENOMEM;
> +
> +	ret = btrfs_search_slot(trans, stripe_root, key, path, -1, 1);
> +	if (ret)
> +		goto err;
> +
> +	ret = btrfs_del_item(trans, stripe_root, path);
> +	if (ret) {
> +		ret = (ret == 1) ? -ENOENT : ret;
> +		goto err;
> +	}
> +
> +	btrfs_free_path(path);
> +
> +	return btrfs_insert_item(trans, stripe_root, key, stripe_extent,
> +				 item_size);
> + err:
> +	btrfs_free_path(path);
> +	return ret;
> +}
> +
>   static int btrfs_insert_one_raid_extent(struct btrfs_trans_handle *trans,
>   					struct btrfs_io_context *bioc)
>   {
> @@ -112,6 +145,9 @@ static int btrfs_insert_one_raid_extent(struct btrfs_trans_handle *trans,
>
>   	ret = btrfs_insert_item(trans, stripe_root, &stripe_key, stripe_extent,
>   				item_size);
> +	if (ret == -EEXIST)
> +		ret = replace_raid_extent_item(trans, &stripe_key,
> +					       stripe_extent, item_size);
>   	if (ret)
>   		btrfs_abort_transaction(trans, ret);
>
>