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

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Message-ID: <56CDF58E.7090307@fb.com>
Date:	Wed, 24 Feb 2016 13:25:18 -0500
From:	Josef Bacik <jbacik@...com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	<kernel-team@...com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] trace-cmd: add trace_hash_find_reverse

On 02/23/2016 05:26 PM, Steven Rostedt wrote:
> 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"
>

Sorry I sent out the wrong version of this patch.  I don't actually need 
this anymore so you can just drop it.  Thanks,

Josef