linux-kernel - Re: [RFC v3 1/7] hashtable: introduce a small and naive hashtable

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Message-ID: <502073E9.8050205@cn.fujitsu.com>
Date:	Tue, 07 Aug 2012 09:48:25 +0800
From:	Li Wei <lw@...fujitsu.com>
To:	Sasha Levin <levinsasha928@...il.com>
CC:	torvalds@...ux-foundation.org, tj@...nel.org,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, paul.gortmaker@...driver.com,
	davem@...emloft.net, rostedt@...dmis.org, mingo@...e.hu,
	ebiederm@...ssion.com, aarcange@...hat.com, ericvh@...il.com,
	netdev@...r.kernel.org, josh@...htriplett.org,
	eric.dumazet@...il.com, mathieu.desnoyers@...icios.com
Subject: Re: [RFC v3 1/7] hashtable: introduce a small and naive hashtable

On 08/07/2012 08:45 AM, Sasha Levin wrote:
> This hashtable implementation is using hlist buckets to provide a simple
> hashtable to prevent it from getting reimplemented all over the kernel.
> 
> Signed-off-by: Sasha Levin <levinsasha928@...il.com>
> ---
>  include/linux/hashtable.h |   82 +++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 82 insertions(+), 0 deletions(-)
>  create mode 100644 include/linux/hashtable.h
> 
> diff --git a/include/linux/hashtable.h b/include/linux/hashtable.h
> new file mode 100644
> index 0000000..394652b
> --- /dev/null
> +++ b/include/linux/hashtable.h
> @@ -0,0 +1,82 @@
> +/*
> + * Hash table implementation
> + * (C) 2012  Sasha Levin <levinsasha928@...il.com>
> + */
> +
> +#ifndef _LINUX_HASHTABLE_H
> +#define _LINUX_HASHTABLE_H
> +
> +#include <linux/list.h>
> +#include <linux/types.h>
> +#include <linux/kernel.h>
> +#include <linux/hash.h>
> +
> +#define DEFINE_HASHTABLE(name, bits)					\
> +	struct hlist_head name[HASH_SIZE(bits)];
> +
> +#define HASH_SIZE(bits) (1 << (bits))
> +
> +/* Use hash_32 when possible to allow for fast 32bit hashing in 64bit kernels. */
> +#define hash_min(val, bits) ((sizeof(val)==4)?hash_32((val), (bits)):hash_long((val), (bits)))
> +
> +/**
> + * hash_init - initialize a hash table
> + * @hashtable: hashtable to be initialized
> + * @bits: bit count of hashing function
> + *
> + * Initializes a hash table with 2**bits buckets.
> + */
> +static inline void hash_init(struct hlist_head *hashtable, int bits)
> +{
> +	int i;
> +
> +	for (i = 0; i < HASH_SIZE(bits); i++)
> +		INIT_HLIST_HEAD(hashtable + i);
> +}
> +
> +/**
> + * hash_add - add an object to a hashtable
> + * @hashtable: hashtable to add to
> + * @bits: bit count used for hashing
> + * @node: the &struct hlist_node of the object to be added
> + * @key: the key of the object to be added
> + */
> +#define hash_add(hashtable, bits, node, key)				\
> +	hlist_add_head(node, &hashtable[hash_min(key, bits)]);
> +
> +/**
> + * hash_del - remove an object from a hashtable
> + * @node: &struct hlist_node of the object to remove
> + */
> +static inline void hash_del(struct hlist_node *node)
> +{
> +	hlist_del_init(node);
> +}
> +
> +/**
> + * hash_for_each - iterate over a hashtable
> + * @name: hashtable to iterate
> + * @bits: bit count of hashing function of the hashtable
> + * @bkt: integer to use as bucket loop cursor
> + * @node: the &struct list_head to use as a loop cursor for each bucket
> + * @obj: the type * to use as a loop cursor for each bucket
> + * @member: the name of the hlist_node within the struct
> + */
> +#define hash_for_each(name, bits, bkt, node, obj, member)		\
> +	for (bkt = 0; bkt < HASH_SIZE(bits); bkt++)			\
> +		hlist_for_each_entry(obj, node, &name[i], member)

Where is the 'i' coming from? maybe &name[bkt]?

> +
> +/**
> + * hash_for_each_possible - iterate over all possible objects for a giver key
> + * @name: hashtable to iterate
> + * @obj: the type * to use as a loop cursor for each bucke
> + * @bits: bit count of hashing function of the hashtable
> + * @node: the &struct list_head to use as a loop cursor for each bucket
> + * @member: the name of the hlist_node within the struct
> + * @key: the key of the objects to iterate over
> + */
> +#define hash_for_each_possible(name, obj, bits, node, member, key)	\
> +	hlist_for_each_entry(obj, node,					\
> +		&name[hash_min(key, bits)], member)
> +
> +#endif
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