linux-kernel - Re: [PATCH] trace-cmd: add trace_hash_find

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Message-ID: <20160223172607.5d377d2a@gandalf.local.home>
Date:	Tue, 23 Feb 2016 17:26:07 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Josef Bacik <jbacik@...com>
Cc:	<kernel-team@...com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] trace-cmd: add trace_hash_find_reverse

On Tue, 15 Dec 2015 11:13:24 -0500
Josef Bacik <jbacik@...com> wrote:

> Sometimes we want to FIFO identical entries in the hash table, so add
> trace_hash_find_reverse, which will cycle through the hash list in reverse.
> This is helpful in our case where we are monitoring block request issues to
> match with their corresponding completes, if we issue multiple times to the same
> block we want to be able to match them with the correct completes (more or less
> anyway).  Thanks,
> 
> Signed-off-by: Josef Bacik <jbacik@...com>
> ---
>  list.h       |  5 +++++
>  trace-hash.c | 22 ++++++++++++++++++++++
>  2 files changed, 27 insertions(+)
> 
> diff --git a/list.h b/list.h
> index 9817871..93c64f5 100644
> --- a/list.h
> +++ b/list.h
> @@ -79,4 +79,9 @@ static inline int list_empty(struct list_head *list)
>  	     &(p)->field != list;					\
>  	     p = n, n = container_of((p)->field.next, typeof(*p), field))
>  
> +#define list_for_each_entry_reverse(p, list, field)			\
> +	for (p = container_of((list)->prev, typeof(*p), field);		\
> +	     &p->field != list;						\
> +	     p = container_of((p)->field.prev, typeof(*p), field))
> +
>  #endif /* __LIST_H */
> diff --git a/trace-hash.c b/trace-hash.c
> index 5ffe61c..0dc4f73 100644
> --- a/trace-hash.c
> +++ b/trace-hash.c
> @@ -94,3 +94,25 @@ trace_hash_find(struct trace_hash *hash, unsigned long long key,
>  
>  	return NULL;
>  }
> +
> +struct trace_hash_item *
> +trace_hash_find_reverse(struct trace_hash *hash, unsigned long long key,
> +			trace_hash_func match, void *data)
> +{
> +	struct trace_hash_item *item;
> +	struct list_head *bucket;
> +	int bucket_nr = hash->power ? key & hash->power :
> +		key % hash->nr_buckets;
> +
> +	bucket = hash->buckets + bucket_nr;
> +	list_for_each_entry_reverse(item, bucket, list) {

Strange, this doesn't compile.

 "struct trace_hash_item has no member named list"

-- Steve

> +		if (item->key == key) {
> +			if (!match)
> +				return item;
> +			if (match(item, data))
> +				return item;
> +		}
> +	}
> +
> +	return NULL;
> +}