On Thu, Apr 04, 2019 at 02:45:29PM +0800, Qu Wenruo wrote:
> Current delayed ref interface has several problems:
> - Longer and longer parameter lists
> bytenr
> num_bytes
> parent
> ---------- so far so good
> ref_root
> owner
> offset
> ---------- I don't feel good now
>
> - Different interpretation for the same parameter
> Above @owner for data ref is inode number (u64),
> while for tree ref, it's level (int).
>
> They are even in different size range.
> For level we only need 0~8, while for ino it's
> BTRFS_FIRST_FREE_OBJECTID~BTRFS_LAST_FREE_OBJECTID.
>
> And @offset doesn't even makes sense for tree ref.
>
> Such parameter reuse may look clever as an hidden union, but it
> destroys code readability.
>
> To solve both problems, we introduce a new structure, btrfs_ref to solve
> them:
>
> - Structure instead of long parameter list
> This makes later expansion easier, and better documented.
>
> - Use btrfs_ref::type to distinguish data and tree ref
>
> - Use proper union to store data/tree ref specific structures.
>
> - Use separate functions to fill data/tree ref data, with a common generic
> function to fill common bytenr/num_bytes members.
>
> All parameters will find its place in btrfs_ref, and an extra member,
> @real_root, inspired by ref-verify code, is newly introduced for later
> qgroup code, to record which tree is triggered this extent modification.
>
> This patch doesn't touch any code, but provides the basis for incoming
> refactors.
>
> Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
> ---
> fs/btrfs/delayed-ref.h | 116 +++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 116 insertions(+)
>
> diff --git a/fs/btrfs/delayed-ref.h b/fs/btrfs/delayed-ref.h
> index 70606da440aa..8eb5b3576759 100644
> --- a/fs/btrfs/delayed-ref.h
> +++ b/fs/btrfs/delayed-ref.h
> @@ -176,6 +176,90 @@ struct btrfs_delayed_ref_root {
> u64 qgroup_to_skip;
> };
>
> +enum btrfs_ref_type {
> + BTRFS_REF_NOT_SET,
> + BTRFS_REF_DATA,
> + BTRFS_REF_METADATA,
> + BTRFS_REF_LAST,
> +};
> +
> +struct btrfs_data_ref {
> + /* For EXTENT_DATA_REF */
> +
> + /* Root who refers to this data extent */
> + u64 ref_root;
> +
> + /* Inode who refers to this data extent */
> + u64 ino;
> +
> + /*
> + * file_offset - extent_offset
> + *
> + * file_offset is the key.offset of the EXTENT_DATA key.
> + * extent_offset is btrfs_file_extent_offset() of the EXTENT_DATA data.
> + */
> + u64 offset;
> +};
> +
> +struct btrfs_tree_ref {
> + /*
> + * Level of this tree block
> + *
> + * Shared for skinny (TREE_BLOCK_REF) and normal tree ref.
> + */
> + int level;
> +
> + /*
> + * Root who refers to this tree block.
> + *
> + * For TREE_BLOCK_REF (skinny metadata, either inline or keyed)
> + */
> + u64 root;
> +
> + /* For non-skinny metadata, no special member needed */
> +};
> +
> +struct btrfs_ref {
The structure name sounds a bit generic, but I think we can keep it
short. There are no other btrfs-specific references that could be
confused, there are 'backrefs', 'delayed-refs' all refering to the
b-tree references.
> + enum btrfs_ref_type type;
> + int action;
> +
> + /*
> + * Only use parent pointers as backref (SHARED_BLOCK_REF or
> + * SHARED_DATA_REF) for this extent and its children.
> + * Set for reloc trees.
> + */
> + bool only_backreferences:1;
No bool bitfields please, wasn't this mentioned last time?
