Re: [PATCH 5/8] btrfs-progs: Add btrfs_uuid_tree_remove

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

On 2021/9/13 下午9:17, Nikolay Borisov wrote:
> It will be used to clear received data on RW snapshots that were
> received.
>
> Signed-off-by: Nikolay Borisov <nborisov@suse.com>
> ---
>   kernel-shared/ctree.h     |  3 ++
>   kernel-shared/uuid-tree.c | 82 +++++++++++++++++++++++++++++++++++++++
>   2 files changed, 85 insertions(+)
>
> diff --git a/kernel-shared/ctree.h b/kernel-shared/ctree.h
> index 91a85796a678..158281a9fd67 100644
> --- a/kernel-shared/ctree.h
> +++ b/kernel-shared/ctree.h
> @@ -2860,6 +2860,9 @@ int btrfs_uuid_tree_add(struct btrfs_trans_handle *trans, u8 *uuid, u8 type,
>   			u64 subvol_id_cpu);
>
>   int btrfs_is_empty_uuid(u8 *uuid);
> +int btrfs_uuid_tree_remove(struct btrfs_trans_handle *trans, u8 *uuid, u8 type,
> +               u64 subid);
> +

I have checked the callers in the incoming check patches, they are all
starting a new trans on uuid tree, thus there is no need to start a
trans out of this function.

Let's just pass the subvolume root into the function, and start a new
trans in side the function.

So that we only need one parameter @root, everything else can be fetched
from @root, and we can also modify the root item and uuid tree just in
one go.

Thanks,
Qu
>
>   static inline int is_fstree(u64 rootid)
>   {
> diff --git a/kernel-shared/uuid-tree.c b/kernel-shared/uuid-tree.c
> index 51a7b5d9ff5d..0f0fbf667dda 100644
> --- a/kernel-shared/uuid-tree.c
> +++ b/kernel-shared/uuid-tree.c
> @@ -120,3 +120,85 @@ int btrfs_is_empty_uuid(u8 *uuid)
>   	}
>   	return 1;
>   }
> +
> +int btrfs_uuid_tree_remove(struct btrfs_trans_handle *trans, u8 *uuid, u8 type,
> +		u64 subid)
> +{
> +	struct btrfs_fs_info *fs_info = trans->fs_info;
> +	struct btrfs_root *uuid_root = fs_info->uuid_root;
> +	int ret;
> +	struct btrfs_path *path = NULL;
> +	struct btrfs_key key;
> +	struct extent_buffer *eb;
> +	int slot;
> +	unsigned long offset;
> +	u32 item_size;
> +	unsigned long move_dst;
> +	unsigned long move_src;
> +	unsigned long move_len;
> +
> +	if (!uuid_root) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	btrfs_uuid_to_key(uuid, &key);
> +	key.type = type;
> +
> +	path = btrfs_alloc_path();
> +	if (!path) {
> +		ret = -ENOMEM;
> +		goto out;
> +	}
> +
> +	ret = btrfs_search_slot(trans, uuid_root, &key, path, -1, 1);
> +	if (ret < 0) {
> +		warning("error %d while searching for uuid item!", ret);
> +		goto out;
> +	}
> +	if (ret > 0) {
> +		ret = -ENOENT;
> +		goto out;
> +	}
> +
> +
> +	eb = path->nodes[0];
> +	slot = path->slots[0];
> +	offset = btrfs_item_ptr_offset(eb, slot);
> +	item_size = btrfs_item_size_nr(eb, slot);
> +	if (!IS_ALIGNED(item_size, sizeof(u64))) {
> +		warning("uuid item with illegal size %lu!",	(unsigned long)item_size);
> +		ret = -ENOENT;
> +		goto out;
> +	}
> +	while (item_size) {
> +		__le64 read_subid;
> +
> +		read_extent_buffer(eb, &read_subid, offset, sizeof(read_subid));
> +		if (le64_to_cpu(read_subid) == subid)
> +			break;
> +		offset += sizeof(read_subid);
> +		item_size -= sizeof(read_subid);
> +	}
> +
> +	if (!item_size) {
> +		ret = -ENOENT;
> +		goto out;
> +	}
> +
> +	item_size = btrfs_item_size_nr(eb, slot);
> +	if (item_size == sizeof(subid)) {
> +		ret = btrfs_del_item(trans, uuid_root, path);
> +		goto out;
> +	}
> +
> +	move_dst = offset;
> +	move_src = offset + sizeof(subid);
> +	move_len = item_size - (move_src - btrfs_item_ptr_offset(eb, slot));
> +	memmove_extent_buffer(eb, move_dst, move_src, move_len);
> +	btrfs_truncate_item(path, item_size - sizeof(subid), 1);
> +
> +out:
> +	btrfs_free_path(path);
> +	return ret;
> +}
>