Subject: Re: [PATCH net-next 1/2] neigh: Factor out ___neigh_lookup_noref

From: Andy Gospodarek <[email-masked]>
Date: Wed, 4 Mar 2015 09:53:31 -0500

On Tue, Mar 03, 2015 at 05:10:44PM -0600, Eric W. Biederman wrote:
> 
> While looking at the mpls code I found myself writing yet another
> version of neigh_lookup_noref.  We currently have __ipv4_lookup_noref
> and __ipv6_lookup_noref.
> 
> So to make my work a little easier and to make it a smidge easier to
> verify/maintain the mpls code in the future I stopped and wrote
> ___neigh_lookup_noref.  Then I rewote __ipv4_lookup_noref and
> __ipv6_lookup_noref in terms of this new function.  I tested my new
> version by verifying that the same code is generated in
> ip_finish_output2 and ip6_finish_output2 where these functions are
> inlined.
> 
> To get to ___neigh_lookup_noref I added a new neighbour cache table
> function key_eq.  So that the static size of the key would be
> available.
> 
> I also added __neigh_lookup_noref for people who want to to lookup
> a neighbour table entry quickly but don't know which neibhgour table
> they are going to look up.

While I understand your intent here, you do really need to know which
neighbour table being used in order to do the look-up with your new
function, so this changelog isn't quite accurate.  I know Dave has
already accepted this patch, but it did not appear in the tree I just
updated, so hopefully there is time to fix this if you agree with me.

I realize patch 2/2 allows one to not specify a table as look-up is done
for you in neigh_xmit, but ___neigh_lookup_noref will clearly panic if
no valid table is passed.

Otherwise the patch-set looks good to me.

Acked-by: Andy Gospodarek <[email-masked]>

> 
> Signed-off-by: "Eric W. Biederman" <[email-masked]>
> ---
>  include/net/arp.h       | 19 ++++--------------
>  include/net/ndisc.h     | 19 +-----------------
>  include/net/neighbour.h | 52 +++++++++++++++++++++++++++++++++++++++++++++++++
>  net/core/neighbour.c    | 20 +++++--------------
>  net/decnet/dn_neigh.c   |  6 ++++++
>  net/ipv4/arp.c          |  9 ++++++++-
>  net/ipv6/ndisc.c        |  7 +++++++
>  7 files changed, 83 insertions(+), 49 deletions(-)
> 
> diff --git a/include/net/arp.h b/include/net/arp.h
> index 21ee1860abbc..5e0f891d476c 100644
> --- a/include/net/arp.h
> +++ b/include/net/arp.h
> @@ -9,28 +9,17 @@
>  
>  extern struct neigh_table arp_tbl;
>  
> -static inline u32 arp_hashfn(u32 key, const struct net_device *dev, u32 hash_rnd)
> +static inline u32 arp_hashfn(const void *pkey, const struct net_device *dev, u32 *hash_rnd)
>  {
> +	u32 key = *(const u32 *)pkey;
>  	u32 val = key ^ hash32_ptr(dev);
>  
> -	return val * hash_rnd;
> +	return val * hash_rnd[0];
>  }
>  
>  static inline struct neighbour *__ipv4_neigh_lookup_noref(struct net_device *dev, u32 key)
>  {
> -	struct neigh_hash_table *nht = rcu_dereference_bh(arp_tbl.nht);
> -	struct neighbour *n;
> -	u32 hash_val;
> -
> -	hash_val = arp_hashfn(key, dev, nht->hash_rnd[0]) >> (32 - nht->hash_shift);
> -	for (n = rcu_dereference_bh(nht->hash_buckets[hash_val]);
> -	     n != NULL;
> -	     n = rcu_dereference_bh(n->next)) {
> -		if (n->dev == dev && *(u32 *)n->primary_key == key)
> -			return n;
> -	}
> -
> -	return NULL;
> +	return ___neigh_lookup_noref(&arp_tbl, neigh_key_eq32, arp_hashfn, &key, dev);
>  }
>  
>  static inline struct neighbour *__ipv4_neigh_lookup(struct net_device *dev, u32 key)
> diff --git a/include/net/ndisc.h b/include/net/ndisc.h
> index 6bbda34d5e59..b3a7751251b4 100644
> --- a/include/net/ndisc.h
> +++ b/include/net/ndisc.h
> @@ -156,24 +156,7 @@ static inline u32 ndisc_hashfn(const void *pkey, const struct net_device *dev, _
>  
>  static inline struct neighbour *__ipv6_neigh_lookup_noref(struct net_device *dev, const void *pkey)
>  {
> -	struct neigh_hash_table *nht;
> -	const u32 *p32 = pkey;
> -	struct neighbour *n;
> -	u32 hash_val;
> -
> -	nht = rcu_dereference_bh(nd_tbl.nht);
> -	hash_val = ndisc_hashfn(pkey, dev, nht->hash_rnd) >> (32 - nht->hash_shift);
> -	for (n = rcu_dereference_bh(nht->hash_buckets[hash_val]);
> -	     n != NULL;
> -	     n = rcu_dereference_bh(n->next)) {
> -		u32 *n32 = (u32 *) n->primary_key;
> -		if (n->dev == dev &&
> -		    ((n32[0] ^ p32[0]) | (n32[1] ^ p32[1]) |
> -		     (n32[2] ^ p32[2]) | (n32[3] ^ p32[3])) == 0)
> -			return n;
> -	}
> -
> -	return NULL;
> +	return ___neigh_lookup_noref(&nd_tbl, neigh_key_eq128, ndisc_hashfn, pkey, dev);
>  }
>  
>  static inline struct neighbour *__ipv6_neigh_lookup(struct net_device *dev, const void *pkey)
> diff --git a/include/net/neighbour.h b/include/net/neighbour.h
> index 9f912e4d4232..14e3f017966b 100644
> --- a/include/net/neighbour.h
> +++ b/include/net/neighbour.h
> @@ -197,6 +197,7 @@ struct neigh_table {
>  	__u32			(*hash)(const void *pkey,
>  					const struct net_device *dev,
>  					__u32 *hash_rnd);
> +	bool			(*key_eq)(const struct neighbour *, const void *pkey);
>  	int			(*constructor)(struct neighbour *);
>  	int			(*pconstructor)(struct pneigh_entry *);
>  	void			(*pdestructor)(struct pneigh_entry *);
> @@ -247,6 +248,57 @@ static inline void *neighbour_priv(const struct neighbour *n)
>  #define NEIGH_UPDATE_F_ISROUTER			0x40000000
>  #define NEIGH_UPDATE_F_ADMIN			0x80000000
>  
> +
> +static inline bool neigh_key_eq16(const struct neighbour *n, const void *pkey)
> +{
> +	return *(const u16 *)n->primary_key == *(const u16 *)pkey;
> +}
> +
> +static inline bool neigh_key_eq32(const struct neighbour *n, const void *pkey)
> +{
> +	return *(const u32 *)n->primary_key == *(const u32 *)pkey;
> +}
> +
> +static inline bool neigh_key_eq128(const struct neighbour *n, const void *pkey)
> +{
> +	const u32 *n32 = (const u32 *)n->primary_key;
> +	const u32 *p32 = pkey;
> +
> +	return ((n32[0] ^ p32[0]) | (n32[1] ^ p32[1]) |
> +		(n32[2] ^ p32[2]) | (n32[3] ^ p32[3])) == 0;
> +}
> +
> +static inline struct neighbour *___neigh_lookup_noref(
> +	struct neigh_table *tbl,
> +	bool (*key_eq)(const struct neighbour *n, const void *pkey),
> +	__u32 (*hash)(const void *pkey,
> +		      const struct net_device *dev,
> +		      __u32 *hash_rnd),
> +	const void *pkey,
> +	struct net_device *dev)
> +{
> +	struct neigh_hash_table *nht = rcu_dereference_bh(tbl->nht);
> +	struct neighbour *n;
> +	u32 hash_val;
> +
> +	hash_val = hash(pkey, dev, nht->hash_rnd) >> (32 - nht->hash_shift);
> +	for (n = rcu_dereference_bh(nht->hash_buckets[hash_val]);
> +	     n != NULL;
> +	     n = rcu_dereference_bh(n->next)) {
> +		if (n->dev == dev && key_eq(n, pkey))
> +			return n;
> +	}
> +
> +	return NULL;
> +}
> +
> +static inline struct neighbour *__neigh_lookup_noref(struct neigh_table *tbl,
> +						     const void *pkey,
> +						     struct net_device *dev)
> +{
> +	return ___neigh_lookup_noref(tbl, tbl->key_eq, tbl->hash, pkey, dev);
> +}
> +
>  void neigh_table_init(int index, struct neigh_table *tbl);
>  int neigh_table_clear(int index, struct neigh_table *tbl);
>  struct neighbour *neigh_lookup(struct neigh_table *tbl, const void *pkey,
> diff --git a/net/core/neighbour.c b/net/core/neighbour.c
> index 0f48ea3affed..fe3c6eac5805 100644
> --- a/net/core/neighbour.c
> +++ b/net/core/neighbour.c
> @@ -397,25 +397,15 @@ struct neighbour *neigh_lookup(struct neigh_table *tbl, const void *pkey,
>  			       struct net_device *dev)
>  {
>  	struct neighbour *n;
> -	int key_len = tbl->key_len;
> -	u32 hash_val;
> -	struct neigh_hash_table *nht;
>  
>  	NEIGH_CACHE_STAT_INC(tbl, lookups);
>  
>  	rcu_read_lock_bh();
> -	nht = rcu_dereference_bh(tbl->nht);
> -	hash_val = tbl->hash(pkey, dev, nht->hash_rnd) >> (32 - nht->hash_shift);
> -
> -	for (n = rcu_dereference_bh(nht->hash_buckets[hash_val]);
> -	     n != NULL;
> -	     n = rcu_dereference_bh(n->next)) {
> -		if (dev == n->dev && !memcmp(n->primary_key, pkey, key_len)) {
> -			if (!atomic_inc_not_zero(&n->refcnt))
> -				n = NULL;
> -			NEIGH_CACHE_STAT_INC(tbl, hits);
> -			break;
> -		}
> +	n = __neigh_lookup_noref(tbl, pkey, dev);
> +	if (n) {
> +		if (!atomic_inc_not_zero(&n->refcnt))
> +			n = NULL;
> +		NEIGH_CACHE_STAT_INC(tbl, hits);
>  	}
>  
>  	rcu_read_unlock_bh();
> diff --git a/net/decnet/dn_neigh.c b/net/decnet/dn_neigh.c
> index f123c6c6748c..ee7d1cef0027 100644
> --- a/net/decnet/dn_neigh.c
> +++ b/net/decnet/dn_neigh.c
> @@ -93,12 +93,18 @@ static u32 dn_neigh_hash(const void *pkey,
>  	return jhash_2words(*(__u16 *)pkey, 0, hash_rnd[0]);
>  }
>  
> +static bool dn_key_eq(const struct neighbour *neigh, const void *pkey)
> +{
> +	return neigh_key_eq16(neigh, pkey);
> +}
> +
>  struct neigh_table dn_neigh_table = {
>  	.family =			PF_DECnet,
>  	.entry_size =			NEIGH_ENTRY_SIZE(sizeof(struct dn_neigh)),
>  	.key_len =			sizeof(__le16),
>  	.protocol =			cpu_to_be16(ETH_P_DNA_RT),
>  	.hash =				dn_neigh_hash,
> +	.key_eq =			dn_key_eq,
>  	.constructor =			dn_neigh_construct,
>  	.id =				"dn_neigh_cache",
>  	.parms ={
> diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
> index 6b8aad6a0d7d..5f5c674e130a 100644
> --- a/net/ipv4/arp.c
> +++ b/net/ipv4/arp.c
> @@ -122,6 +122,7 @@
>   *	Interface to generic neighbour cache.
>   */
>  static u32 arp_hash(const void *pkey, const struct net_device *dev, __u32 *hash_rnd);
> +static bool arp_key_eq(const struct neighbour *n, const void *pkey);
>  static int arp_constructor(struct neighbour *neigh);
>  static void arp_solicit(struct neighbour *neigh, struct sk_buff *skb);
>  static void arp_error_report(struct neighbour *neigh, struct sk_buff *skb);
> @@ -154,6 +155,7 @@ struct neigh_table arp_tbl = {
>  	.key_len	= 4,
>  	.protocol	= cpu_to_be16(ETH_P_IP),
>  	.hash		= arp_hash,
> +	.key_eq		= arp_key_eq,
>  	.constructor	= arp_constructor,
>  	.proxy_redo	= parp_redo,
>  	.id		= "arp_cache",
> @@ -209,7 +211,12 @@ static u32 arp_hash(const void *pkey,
>  		    const struct net_device *dev,
>  		    __u32 *hash_rnd)
>  {
> -	return arp_hashfn(*(u32 *)pkey, dev, *hash_rnd);
> +	return arp_hashfn(pkey, dev, hash_rnd);
> +}
> +
> +static bool arp_key_eq(const struct neighbour *neigh, const void *pkey)
> +{
> +	return neigh_key_eq32(neigh, pkey);
>  }
>  
>  static int arp_constructor(struct neighbour *neigh)
> diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
> index e363bbc2420d..247ad7c298f7 100644
> --- a/net/ipv6/ndisc.c
> +++ b/net/ipv6/ndisc.c
> @@ -84,6 +84,7 @@ do {								\
>  static u32 ndisc_hash(const void *pkey,
>  		      const struct net_device *dev,
>  		      __u32 *hash_rnd);
> +static bool ndisc_key_eq(const struct neighbour *neigh, const void *pkey);
>  static int ndisc_constructor(struct neighbour *neigh);
>  static void ndisc_solicit(struct neighbour *neigh, struct sk_buff *skb);
>  static void ndisc_error_report(struct neighbour *neigh, struct sk_buff *skb);
> @@ -119,6 +120,7 @@ struct neigh_table nd_tbl = {
>  	.key_len =	sizeof(struct in6_addr),
>  	.protocol =	cpu_to_be16(ETH_P_IPV6),
>  	.hash =		ndisc_hash,
> +	.key_eq =	ndisc_key_eq,
>  	.constructor =	ndisc_constructor,
>  	.pconstructor =	pndisc_constructor,
>  	.pdestructor =	pndisc_destructor,
> @@ -295,6 +297,11 @@ static u32 ndisc_hash(const void *pkey,
>  	return ndisc_hashfn(pkey, dev, hash_rnd);
>  }
>  
> +static bool ndisc_key_eq(const struct neighbour *n, const void *pkey)
> +{
> +	return neigh_key_eq128(n, pkey);
> +}
> +
>  static int ndisc_constructor(struct neighbour *neigh)
>  {
>  	struct in6_addr *addr = (struct in6_addr *)&neigh->primary_key;
> -- 
> 2.2.1
> 
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