Re: [PATCH v3 1/2] btrfs: Add support to do stack item key operation

[Qu Wenruo <quwenruo@cn.fujitsu.com>]

Hi David,

I'm sorry that I didn't get the point of your previous comment.

Maybe the parameter/function name don't follow BTRFS_STACK_GETSET_FUNC 
macro, but IMHO that's OK, as btrfs_item_key_to_cpu() is not an accessor 
following that macro definition.
It's called even before we get needed data structure, so I think the 
declaration should be OK.

BTW, I really hope the fix can be merged before v4.3, as such fix is 
quite small, while the bug itself impacts qgroup quite a lot.

Thanks,
Qu

Qu Wenruo wrote on 2015/10/07 09:08 +0800:
> Normal btrfs_item_key_to_cpu() will need extent buffer to do it, and
> there is not stack version to handle in memory leaf.
>
> Add btrfs_stack_item_key_to_cpu() function for such operation, which
> will provide the basis for later qgroup fix.
>
> Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
> ---
> v2:
>    Change the char* parameter to struct btrfs_header *, as a leaf always
>    has a header.
> v3:
>    Fix a bug caused in type change of stack_leaf.
> ---
>   fs/btrfs/ctree.h | 20 ++++++++++++++++++++
>   1 file changed, 20 insertions(+)
>
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index 938efe3..b824fe2 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -2683,6 +2683,17 @@ static inline void btrfs_item_key(struct extent_buffer *eb,
>   	read_eb_member(eb, item, struct btrfs_item, key, disk_key);
>   }
>
> +static inline void btrfs_stack_item_key(struct btrfs_header *stack_leaf,
> +					struct btrfs_disk_key *disk_key,
> +					int nr)
> +{
> +	unsigned long item_offset = btrfs_item_nr_offset(nr);
> +	struct btrfs_item *item;
> +
> +	item = (struct btrfs_item *)((char *)(stack_leaf) + item_offset);
> +	memcpy(disk_key, &item->key, sizeof(*disk_key));
> +}
> +
>   static inline void btrfs_set_item_key(struct extent_buffer *eb,
>   			       struct btrfs_disk_key *disk_key, int nr)
>   {
> @@ -2785,6 +2796,15 @@ static inline void btrfs_item_key_to_cpu(struct extent_buffer *eb,
>   	btrfs_disk_key_to_cpu(key, &disk_key);
>   }
>
> +static inline void btrfs_stack_item_key_to_cpu(struct btrfs_header *stack_leaf,
> +					       struct btrfs_key *key,
> +					       int nr)
> +{
> +	struct btrfs_disk_key disk_key;
> +	btrfs_stack_item_key(stack_leaf, &disk_key, nr);
> +	btrfs_disk_key_to_cpu(key, &disk_key);
> +}
> +
>   static inline void btrfs_dir_item_key_to_cpu(struct extent_buffer *eb,
>   				      struct btrfs_dir_item *item,
>   				      struct btrfs_key *key)
>