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SubjectRe: [PATCH RFC 01/14] block, bfq: introduce the BFQ-v0 I/O scheduler as an extra scheduler
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> Il giorno 07 mar 2017, alle ore 18:22, Jens Axboe <axboe@kernel.dk> ha scritto:
>
>> +/**
>> + * bfq_entity_of - get an entity from a node.
>> + * @node: the node field of the entity.
>> + *
>> + * Convert a node pointer to the relative entity. This is used only
>> + * to simplify the logic of some functions and not as the generic
>> + * conversion mechanism because, e.g., in the tree walking functions,
>> + * the check for a %NULL value would be redundant.
>> + */
>> +static struct bfq_entity *bfq_entity_of(struct rb_node *node)
>> +{
>> + struct bfq_entity *entity = NULL;
>> +
>> + if (node)
>> + entity = rb_entry(node, struct bfq_entity, rb_node);
>> +
>> + return entity;
>> +}
>
> Get rid of pointless wrappers like this, just use rb_entry() in the
> caller. It's harmful to the readability of the code to have to lookup
> things like this, if it's a list_entry or rb_entry() in the caller you
> know exactly what is going on immediately.
>


Ok. Just a quick request for help about this. The code seems to become
quite ugly with a verbatim replacement of this function with its body
(and there are several occurrences of it), so there is probably something I'm
missing. For example, given the following loop:

for (; entity ; entity = bfq_entity_of(rb_first(active)))
bfq_reparent_leaf_entity(bfqd, entity);

the only non-cryptic, but heavier solution I see is:

for (; entity ; ) {
bfq_reparent_leaf_entity(bfqd, entity);
if (rb_first(active))
entity = rb_entry(rb_first(active), struct bfq_entity, rb_node);
else
entity = NULL;
}

Am I missing something? Or are these extra lines of code a reasonable
price to pay for increased transparency?

Thanks,
Paolo

> --
> Jens Axboe
>

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