On 2020-05-08 16:32, Bart Van Assche wrote:
> On 2020-05-04 19:09, Ming Lei wrote:
>> @@ -310,19 +313,30 @@ static void bt_tags_for_each(struct blk_mq_tags *tags, struct sbitmap_queue *bt,
>> /**
>> * blk_mq_all_tag_busy_iter - iterate over all started requests in a tag map
>> * @tags: Tag map to iterate over.
>> - * @fn: Pointer to the function that will be called for each started
>> - * request. @fn will be called as follows: @fn(rq, @priv,
>> - * reserved) where rq is a pointer to a request. 'reserved'
>> - * indicates whether or not @rq is a reserved request. Return
>> - * true to continue iterating tags, false to stop.
>> + * @fn: Pointer to the function that will be called for each request
>> + * when .busy_rq_fn(rq) returns true. @fn will be called as
>> + * follows: @fn(rq, @priv, reserved) where rq is a pointer to a
>> + * request. 'reserved' indicates whether or not @rq is a reserved
>> + * request. Return true to continue iterating tags, false to stop.
>> + * @busy_rq_fn: Pointer to the function that will be called for each request,
>> + * @busy_rq_fn's type is same with @fn. Only when @busy_rq_fn(rq,
>> + * @priv, reserved) returns true, @fn will be called on this rq.
>> * @priv: Will be passed as second argument to @fn.
>> */
>> -static void blk_mq_all_tag_busy_iter(struct blk_mq_tags *tags,
>> - busy_tag_iter_fn *fn, void *priv)
>> +void blk_mq_all_tag_busy_iter(struct blk_mq_tags *tags,
>> + busy_tag_iter_fn *fn, busy_rq_iter_fn *busy_rq_fn,
>> + void *priv)
>> {
>
> The name 'busy_rq_fn' is not ideal because it is named after one
> specific use case, namely checking whether or not a request is busy (has
> already been started). How about using the name 'pred_fn' ('pred' from
> predicate because it controls whether the other function is called)?
> Since only the context that passes 'fn' can know what data structure
> 'priv' points to and since 'busy_rq_fn' is passed from another context,
> can 'busy_rq_fn' even know what data 'priv' points at? Has it been
> considered not to pass the 'priv' argument to 'busy_rq_fn'?
Thinking further about this, another possible approach is not to modify
blk_mq_all_tag_busy_iter() at all and to introduce a new function that
iterates over all requests instead of only over busy requests. I think
that approach will result in easier to read code than patch 5/11 because
each of these request iteration functions will only accept a single
callback function pointer. Additionally, that approach will make the
following function superfluous (from patch 7/11):
+static bool blk_mq_inflight_rq(struct request *rq, void *data,
+ bool reserved)
+{
+ return rq->tag >= 0;
+}
Thanks,
Bart.
