On 2018年03月27日 15:06, Lu Fengqi wrote:
> The function will find the root_item specified by the subvol_id,
> clear the BTRFS_ROOT_SUBVOL_DEAD flag and set root_refs to one.

Sorry I didn't point it out in btrfs_link_subvol() patch, but at least
to me, refs should only be modified by btrfs_link_subvol(), just like
btrfs_unlink().

Thanks,
Qu

> 
> Signed-off-by: Lu Fengqi <lufq.fnst@cn.fujitsu.com>
> ---
>  ctree.h           |  1 +
>  undelete-subvol.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 56 insertions(+)
> 
> diff --git a/ctree.h b/ctree.h
> index 4bff0b821472..7c0b8150bc4e 100644
> --- a/ctree.h
> +++ b/ctree.h
> @@ -184,6 +184,7 @@ static int btrfs_csum_sizes[] = { 4 };
>  #define BTRFS_FT_MAX		9
>  
>  #define BTRFS_ROOT_SUBVOL_RDONLY	(1ULL << 0)
> +#define BTRFS_ROOT_SUBVOL_DEAD		(1ULL << 48)
>  
>  /*
>   * the key defines the order in the tree, and so it also defines (optimal)
> diff --git a/undelete-subvol.c b/undelete-subvol.c
> index 00fcc4895778..781057df2b84 100644
> --- a/undelete-subvol.c
> +++ b/undelete-subvol.c
> @@ -12,6 +12,9 @@
>   */
>  
>  #include "ctree.h"
> +#include "transaction.h"
> +#include "disk-io.h"
> +#include "messages.h"
>  
>  /*
>   * Determines whether the subvolume is intact, according to the drop_progress
> @@ -51,3 +54,55 @@ out:
>  	btrfs_release_path(&path);
>  	return ret;
>  }
> +
> +/*
> + * Clear BTRFS_ROOT_SUBVOL_DEAD flag and set the root_refs to one.
> + *
> + * @root	the root of root tree.
> + * @subvol_id	specify the root_item which will be modified.
> + *
> + * Return 0 if no error occurred.
> + */
> +static int recover_dead_root(struct btrfs_trans_handle *trans,
> +			     struct btrfs_root *root, u64 subvol_id)
> +{
> +	struct btrfs_key key;
> +	struct btrfs_path path;
> +	struct extent_buffer *leaf;
> +	struct btrfs_root_item root_item;
> +	u64 root_flags;
> +	u64 offset;
> +	int ret;
> +
> +	key.objectid = subvol_id;
> +	key.type = BTRFS_ROOT_ITEM_KEY;
> +	key.offset = 0;
> +
> +	btrfs_init_path(&path);
> +	ret = btrfs_search_slot(trans, root, &key, &path, 0, 0);
> +	if (ret) {
> +		error("couldn't find ROOT_ITEM for %llu failed: %d",
> +				subvol_id, ret);
> +		goto out;
> +	}
> +
> +	leaf = path.nodes[0];
> +
> +	offset = btrfs_item_ptr_offset(leaf, path.slots[0]);
> +	read_extent_buffer(leaf, &root_item, offset, sizeof(root_item));
> +
> +	/* Clear BTRFS_ROOT_SUBVOL_DEAD */
> +	root_flags = btrfs_root_flags(&root_item);
> +	btrfs_set_root_flags(&root_item,
> +			     root_flags & ~BTRFS_ROOT_SUBVOL_DEAD);
> +
> +	/* Increase the refs */
> +	btrfs_set_root_refs(&root_item, 1);
> +
> +	write_extent_buffer(leaf, &root_item, offset, sizeof(root_item));
> +	btrfs_mark_buffer_dirty(leaf);
> +
> +out:
> +	btrfs_release_path(&path);
> +	return ret;
> +}
>