On 6.12.18 г. 8:58 ч., Qu Wenruo wrote:
> Current delayed ref interface has several problems:
> - Longer and longer parameter lists
> bytenr
> num_bytes
> parent
> ref_root
> owner
> offset
> for_reloc << Only qgroup code cares.
>
> - Different interpretation for the same parameter
> Above @owner for data ref is ino owning this extent,
> while for tree ref, it's level. 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 | 109 +++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 109 insertions(+)
>
> diff --git a/fs/btrfs/delayed-ref.h b/fs/btrfs/delayed-ref.h
> index d8fa12d3f2cc..e36d6b05d85e 100644
> --- a/fs/btrfs/delayed-ref.h
> +++ b/fs/btrfs/delayed-ref.h
> @@ -176,6 +176,81 @@ struct btrfs_delayed_ref_root {
> u64 qgroup_to_skip;
> };
>
> +enum btrfs_ref_type {
> + BTRFS_REF_NOT_SET = 0,
No need for explicit initialisation when your enums start from 0.
> + BTRFS_REF_DATA,
> + BTRFS_REF_METADATA,
> + BTRFS_REF_LAST,
> +};
> +
> +struct btrfs_data_ref {
> + /*
> + * For EXTENT_DATA_REF
> + *
> + * @ref_root: current owner of the extent.
> + * may differ from btrfs_ref::real_root.
Here 'owner' is a bit ambiguous. Isn't this the root of the owner
> + * @ino: inode number of the owner.
And the owner is really the owning inode?
> + * @offset: *CALCULATED* offset. Not EXTENT_DATA key offset.
What does calculated mean here?
> + *
> + */
Ugh, this is ugly, why not have a single /* */ line above each member
and document them like that?
> + u64 ref_root;
> + u64 ino;
> + u64 offset;
> +};
> +
> +struct btrfs_tree_ref {
> + /* Common for all sub types and skinny combination */
> + int level;
Like you've done here. Mention that this is the level in the tree that
this reference is located at.
> +
> + /*
> + * For TREE_BLOCK_REF (skinny metadata, either inline or keyed)
> + *
> + * root here may differ from btrfs_ref::real_root.
> + */
Make it refer to the documentation of the generic btrfs_ref structure
because if someone reads this comment and doesn't read the one in
btrfs_ref then it's not clear under what conditions they might differ.
> + u64 root;
> +
> + /* For non-skinny metadata, no special member needed */
> +};
> +
> +struct btrfs_ref {
> + enum btrfs_ref_type type;
> + int action;
> +
> + /*
> + * Use full backref(SHARED_BLOCK_REF or SHARED_DATA_REF) for this
> + * extent and its children.
> + * Set for reloc trees.
> + */
> + unsigned int use_fullback:1;
'fullback' is too terse, use_backreferences or something conveying more
information? Also please use explicit bool type:
bool xxxx:1
> +
> + /*
> + * Whether this extent should go through qgroup record.
> + * Normally false, but for certain case like delayed subtree scan,
> + * this can hugely reduce qgroup overhead.
> + */
> + unsigned int skip_qgroup:1;
again, explicit bool type please.
> +
> + /*
> + * Who owns this reference modification, optional.
> + *
> + * One example:
> + * When creating reloc tree for source fs, it will increase tree block
> + * ref for children tree blocks.
> + * In that case, btrfs_ref::real_root = reloc tree,
> + * while btrfs_ref::tree_ref::root = fs tree.
> + */
> + u64 real_root;
> + u64 bytenr;
> + u64 len;
> +
> + /* Common @parent for SHARED_DATA_REF/SHARED_BLOCK_REF */
OK, it's common but what does it really contain? Either document it or
rename it to parent_block or something.
> + u64 parent;
> + union {
> + struct btrfs_data_ref data_ref;
> + struct btrfs_tree_ref tree_ref;
> + };
> +};
> +
> extern struct kmem_cache *btrfs_delayed_ref_head_cachep;
> extern struct kmem_cache *btrfs_delayed_tree_ref_cachep;
> extern struct kmem_cache *btrfs_delayed_data_ref_cachep;
> @@ -184,6 +259,40 @@ extern struct kmem_cache *btrfs_delayed_extent_op_cachep;
> int __init btrfs_delayed_ref_init(void);
> void __cold btrfs_delayed_ref_exit(void);
>
> +static inline void btrfs_init_generic_ref(struct btrfs_ref *generic_ref,
> + int action, u64 bytenr, u64 len, u64 real_root,
> + u64 parent)
> +{
> + generic_ref->action = action;
IMO it makes sense in this series to have a patch which converts the
action defines to an enum and subsequently modify functions/structs to
actually be of enum type.
> + generic_ref->bytenr = bytenr;
> + generic_ref->len = len;
> + generic_ref->real_root = real_root;
> + generic_ref->parent = parent;
> +}
> +
> +static inline void btrfs_init_tree_ref(struct btrfs_ref *generic_ref,
> + int level, u64 root)
> +{
> + /* If @real_root not set, use @root as fallback */
> + if (!generic_ref->real_root)
> + generic_ref->real_root = root;
> + generic_ref->tree_ref.level = level;
> + generic_ref->tree_ref.root = root;
> + generic_ref->type = BTRFS_REF_METADATA;
> +}
> +
> +static inline void btrfs_init_data_ref(struct btrfs_ref *generic_ref,
> + u64 ref_root, u64 ino, u64 offset)
> +{
> + /* If @real_root not set, use @root as fallback */
> + if (!generic_ref->real_root)
> + generic_ref->real_root = ref_root;
> + generic_ref->data_ref.ref_root = ref_root;
> + generic_ref->data_ref.ino = ino;
> + generic_ref->data_ref.offset = offset;
> + generic_ref->type = BTRFS_REF_DATA;
> +}
> +
> static inline struct btrfs_delayed_extent_op *
> btrfs_alloc_delayed_extent_op(void)
> {
>
