[PATCH] fib_trie: coding style: Use pointer after check

[PATCH] fib_trie: coding style: Use pointer after check

[Firo Yang]

As Alexander Duyck pointed out that:
struct tnode {
        ...
        struct key_vector kv[1];
}
The kv[1] member of struct tnode is an arry that refernced by
a null pointer will not crash the system, like this:
struct tnode *p = NULL;
struct key_vector *kv = p->kv;
As such p->kv doesn't actually dereference anything, it is simply a
means for getting the offset to the array from the pointer kv.

This patch make the code more regular to avoid making people feel
odd when they look at the code.

Signed-off-by: Firo Yang <firogm@gmail.com>
---
 net/ipv4/fib_trie.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index 01bce15..2af2d07 100644
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -325,13 +325,15 @@ static inline void empty_child_dec(struct key_vector *n)
 
 static struct key_vector *leaf_new(t_key key, struct fib_alias *fa)
 {
-	struct tnode *kv = kmem_cache_alloc(trie_leaf_kmem, GFP_KERNEL);
-	struct key_vector *l = kv->kv;
+	struct tnode *kv;
+	struct key_vector *l;
 
+	kv = kmem_cache_alloc(trie_leaf_kmem, GFP_KERNEL);
 	if (!kv)
 		return NULL;
 
 	/* initialize key vector */
+	l = kv->kv;
 	l->key = key;
 	l->pos = 0;
 	l->bits = 0;
@@ -346,24 +348,26 @@ static struct key_vector *leaf_new(t_key key, struct fib_alias *fa)
 
 static struct key_vector *tnode_new(t_key key, int pos, int bits)
 {
-	struct tnode *tnode = tnode_alloc(bits);
+	struct tnode *tnode;
 	unsigned int shift = pos + bits;
-	struct key_vector *tn = tnode->kv;
+	struct key_vector *tn;
 
 	/* verify bits and pos their msb bits clear and values are valid */
 	BUG_ON(!bits || (shift > KEYLENGTH));
 
-	pr_debug("AT %p s=%zu %zu\n", tnode, TNODE_SIZE(0),
-		 sizeof(struct key_vector *) << bits);
-
+	tnode = tnode_alloc(bits);
 	if (!tnode)
 		return NULL;
 
+	pr_debug("AT %p s=%zu %zu\n", tnode, TNODE_SIZE(0),
+		 sizeof(struct key_vector *) << bits);
+
 	if (bits = KEYLENGTH)
 		tnode->full_children = 1;
 	else
 		tnode->empty_children = 1ul << bits;
 
+	tn = tnode->kv;
 	tn->key = (shift < KEYLENGTH) ? (key >> shift) << shift : 0;
 	tn->pos = pos;
 	tn->bits = bits;
@@ -2054,11 +2058,12 @@ static struct key_vector *fib_trie_get_next(struct fib_trie_iter *iter)
 static struct key_vector *fib_trie_get_first(struct fib_trie_iter *iter,
 					     struct trie *t)
 {
-	struct key_vector *n, *pn = t->kv;
+	struct key_vector *n, *pn;
 
 	if (!t)
 		return NULL;
 
+	pn = t->kv;
 	n = rcu_dereference(pn->tnode[0]);
 	if (!n)
 		return NULL;
-- 
2.4.2

Re: [PATCH] fib_trie: coding style: Use pointer after check

[Alexander Duyck]

On 06/07/2015 07:47 AM, Firo Yang wrote:
> As Alexander Duyck pointed out that:
> struct tnode {
>          ...
>          struct key_vector kv[1];
> }
> The kv[1] member of struct tnode is an arry that refernced by
> a null pointer will not crash the system, like this:
> struct tnode *p = NULL;
> struct key_vector *kv = p->kv;
> As such p->kv doesn't actually dereference anything, it is simply a
> means for getting the offset to the array from the pointer kv.
>
> This patch make the code more regular to avoid making people feel
> odd when they look at the code.
>
> Signed-off-by: Firo Yang <firogm@gmail.com>

Overall this patch looks good.  Just a few minor items called out below. 
  With those corrected you would probably be good to submit to netdev.

> ---
>   net/ipv4/fib_trie.c | 21 +++++++++++++--------
>   1 file changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
> index 01bce15..2af2d07 100644
> --- a/net/ipv4/fib_trie.c
> +++ b/net/ipv4/fib_trie.c
> @@ -325,13 +325,15 @@ static inline void empty_child_dec(struct key_vector *n)
>
>   static struct key_vector *leaf_new(t_key key, struct fib_alias *fa)
>   {
> -	struct tnode *kv = kmem_cache_alloc(trie_leaf_kmem, GFP_KERNEL);
> -	struct key_vector *l = kv->kv;
> +	struct tnode *kv;
> +	struct key_vector *l;
>

Dave Miller usually prefers it if variables are ordered from longest to 
shortest.  So you should probably have l defined first, and then kv.

> +	kv = kmem_cache_alloc(trie_leaf_kmem, GFP_KERNEL);
>   	if (!kv)
>   		return NULL;
>
>   	/* initialize key vector */
> +	l = kv->kv;
>   	l->key = key;
>   	l->pos = 0;
>   	l->bits = 0;
> @@ -346,24 +348,26 @@ static struct key_vector *leaf_new(t_key key, struct fib_alias *fa)
>
>   static struct key_vector *tnode_new(t_key key, int pos, int bits)
>   {
> -	struct tnode *tnode = tnode_alloc(bits);
> +	struct tnode *tnode;
>   	unsigned int shift = pos + bits;
> -	struct key_vector *tn = tnode->kv;
> +	struct key_vector *tn;
>

Same here.  Since tnode is the shorter variable declaration it should be 
declared at the end of the list instead of the start.

>   	/* verify bits and pos their msb bits clear and values are valid */
>   	BUG_ON(!bits || (shift > KEYLENGTH));
>
> -	pr_debug("AT %p s=%zu %zu\n", tnode, TNODE_SIZE(0),
> -		 sizeof(struct key_vector *) << bits);
> -
> +	tnode = tnode_alloc(bits);
>   	if (!tnode)
>   		return NULL;
>
> +	pr_debug("AT %p s=%zu %zu\n", tnode, TNODE_SIZE(0),
> +		 sizeof(struct key_vector *) << bits);
> +
>   	if (bits = KEYLENGTH)
>   		tnode->full_children = 1;
>   	else
>   		tnode->empty_children = 1ul << bits;
>
> +	tn = tnode->kv;
>   	tn->key = (shift < KEYLENGTH) ? (key >> shift) << shift : 0;
>   	tn->pos = pos;
>   	tn->bits = bits;
> @@ -2054,11 +2058,12 @@ static struct key_vector *fib_trie_get_next(struct fib_trie_iter *iter)
>   static struct key_vector *fib_trie_get_first(struct fib_trie_iter *iter,
>   					     struct trie *t)
>   {
> -	struct key_vector *n, *pn = t->kv;
> +	struct key_vector *n, *pn;
>
>   	if (!t)
>   		return NULL;
>
> +	pn = t->kv;
>   	n = rcu_dereference(pn->tnode[0]);
>   	if (!n)
>   		return NULL;
>

Re: [PATCH] fib_trie: coding style: Use pointer after check

[Firo Yang]

On Sun, Jun 07, 2015 at 09:50:32AM -0700, Alexander Duyck wrote:
>On 06/07/2015 07:47 AM, Firo Yang wrote:
>>As Alexander Duyck pointed out that:
>>struct tnode {
>>         ...
>>         struct key_vector kv[1];
>>}
>>The kv[1] member of struct tnode is an arry that refernced by
>>a null pointer will not crash the system, like this:
>>struct tnode *p = NULL;
>>struct key_vector *kv = p->kv;
>>As such p->kv doesn't actually dereference anything, it is simply a
>>means for getting the offset to the array from the pointer kv.
>>
>>This patch make the code more regular to avoid making people feel
>>odd when they look at the code.
>>
>>Signed-off-by: Firo Yang <firogm@gmail.com>
>
>Overall this patch looks good.  Just a few minor items called out below.
>With those corrected you would probably be good to submit to netdev.

Thanks Alex for your kind advices.
I will correct them.
>
>>---
>>  net/ipv4/fib_trie.c | 21 +++++++++++++--------
>>  1 file changed, 13 insertions(+), 8 deletions(-)
>>
>>diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
>>index 01bce15..2af2d07 100644
>>--- a/net/ipv4/fib_trie.c
>>+++ b/net/ipv4/fib_trie.c
>>@@ -325,13 +325,15 @@ static inline void empty_child_dec(struct key_vector *n)
>>
>>  static struct key_vector *leaf_new(t_key key, struct fib_alias *fa)
>>  {
>>-	struct tnode *kv = kmem_cache_alloc(trie_leaf_kmem, GFP_KERNEL);
>>-	struct key_vector *l = kv->kv;
>>+	struct tnode *kv;
>>+	struct key_vector *l;
>>
>
>Dave Miller usually prefers it if variables are ordered from longest to
>shortest.  So you should probably have l defined first, and then kv.
>
>>+	kv = kmem_cache_alloc(trie_leaf_kmem, GFP_KERNEL);
>>  	if (!kv)
>>  		return NULL;
>>
>>  	/* initialize key vector */
>>+	l = kv->kv;
>>  	l->key = key;
>>  	l->pos = 0;
>>  	l->bits = 0;
>>@@ -346,24 +348,26 @@ static struct key_vector *leaf_new(t_key key, struct fib_alias *fa)
>>
>>  static struct key_vector *tnode_new(t_key key, int pos, int bits)
>>  {
>>-	struct tnode *tnode = tnode_alloc(bits);
>>+	struct tnode *tnode;
>>  	unsigned int shift = pos + bits;
>>-	struct key_vector *tn = tnode->kv;
>>+	struct key_vector *tn;
>>
>
>Same here.  Since tnode is the shorter variable declaration it should be
>declared at the end of the list instead of the start.
>
>>  	/* verify bits and pos their msb bits clear and values are valid */
>>  	BUG_ON(!bits || (shift > KEYLENGTH));
>>
>>-	pr_debug("AT %p s=%zu %zu\n", tnode, TNODE_SIZE(0),
>>-		 sizeof(struct key_vector *) << bits);
>>-
>>+	tnode = tnode_alloc(bits);
>>  	if (!tnode)
>>  		return NULL;
>>
>>+	pr_debug("AT %p s=%zu %zu\n", tnode, TNODE_SIZE(0),
>>+		 sizeof(struct key_vector *) << bits);
>>+
>>  	if (bits = KEYLENGTH)
>>  		tnode->full_children = 1;
>>  	else
>>  		tnode->empty_children = 1ul << bits;
>>
>>+	tn = tnode->kv;
>>  	tn->key = (shift < KEYLENGTH) ? (key >> shift) << shift : 0;
>>  	tn->pos = pos;
>>  	tn->bits = bits;
>>@@ -2054,11 +2058,12 @@ static struct key_vector *fib_trie_get_next(struct fib_trie_iter *iter)
>>  static struct key_vector *fib_trie_get_first(struct fib_trie_iter *iter,
>>  					     struct trie *t)
>>  {
>>-	struct key_vector *n, *pn = t->kv;
>>+	struct key_vector *n, *pn;
>>
>>  	if (!t)
>>  		return NULL;
>>
>>+	pn = t->kv;
>>  	n = rcu_dereference(pn->tnode[0]);
>>  	if (!n)
>>  		return NULL;
>>
>

-- 

[PATCH] fib_trie: coding style: Use pointer after check

[Firo Yang]

As Alexander Duyck pointed out that:
struct tnode {
        ...
        struct key_vector kv[1];
}
The kv[1] member of struct tnode is an arry that refernced by
a null pointer will not crash the system, like this:
struct tnode *p = NULL;
struct key_vector *kv = p->kv;
As such p->kv doesn't actually dereference anything, it is simply a
means for getting the offset to the array from the pointer p.

This patch make the code more regular to avoid making people feel
odd when they look at the code.

Signed-off-by: Firo Yang <firogm@gmail.com>
---
 net/ipv4/fib_trie.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index 01bce15..3c699c4 100644
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -325,13 +325,15 @@ static inline void empty_child_dec(struct key_vector *n)
 
 static struct key_vector *leaf_new(t_key key, struct fib_alias *fa)
 {
-	struct tnode *kv = kmem_cache_alloc(trie_leaf_kmem, GFP_KERNEL);
-	struct key_vector *l = kv->kv;
+	struct key_vector *l;
+	struct tnode *kv;
 
+	kv = kmem_cache_alloc(trie_leaf_kmem, GFP_KERNEL);
 	if (!kv)
 		return NULL;
 
 	/* initialize key vector */
+	l = kv->kv;
 	l->key = key;
 	l->pos = 0;
 	l->bits = 0;
@@ -346,24 +348,26 @@ static struct key_vector *leaf_new(t_key key, struct fib_alias *fa)
 
 static struct key_vector *tnode_new(t_key key, int pos, int bits)
 {
-	struct tnode *tnode = tnode_alloc(bits);
 	unsigned int shift = pos + bits;
-	struct key_vector *tn = tnode->kv;
+	struct key_vector *tn;
+	struct tnode *tnode;
 
 	/* verify bits and pos their msb bits clear and values are valid */
 	BUG_ON(!bits || (shift > KEYLENGTH));
 
-	pr_debug("AT %p s=%zu %zu\n", tnode, TNODE_SIZE(0),
-		 sizeof(struct key_vector *) << bits);
-
+	tnode = tnode_alloc(bits);
 	if (!tnode)
 		return NULL;
 
+	pr_debug("AT %p s=%zu %zu\n", tnode, TNODE_SIZE(0),
+		 sizeof(struct key_vector *) << bits);
+
 	if (bits = KEYLENGTH)
 		tnode->full_children = 1;
 	else
 		tnode->empty_children = 1ul << bits;
 
+	tn = tnode->kv;
 	tn->key = (shift < KEYLENGTH) ? (key >> shift) << shift : 0;
 	tn->pos = pos;
 	tn->bits = bits;
@@ -2054,11 +2058,12 @@ static struct key_vector *fib_trie_get_next(struct fib_trie_iter *iter)
 static struct key_vector *fib_trie_get_first(struct fib_trie_iter *iter,
 					     struct trie *t)
 {
-	struct key_vector *n, *pn = t->kv;
+	struct key_vector *n, *pn;
 
 	if (!t)
 		return NULL;
 
+	pn = t->kv;
 	n = rcu_dereference(pn->tnode[0]);
 	if (!n)
 		return NULL;
-- 
2.4.2

[PATCH] fib_trie: coding style: Use pointer after check

[Firo Yang]

As Alexander Duyck pointed out that:
struct tnode {
        ...
        struct key_vector kv[1];
}
The kv[1] member of struct tnode is an arry that refernced by
a null pointer will not crash the system, like this:
struct tnode *p = NULL;
struct key_vector *kv = p->kv;
As such p->kv doesn't actually dereference anything, it is simply a
means for getting the offset to the array from the pointer p.

This patch make the code more regular to avoid making people feel
odd when they look at the code.

Signed-off-by: Firo Yang <firogm@gmail.com>
---
 net/ipv4/fib_trie.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index 01bce15..3c699c4 100644
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -325,13 +325,15 @@ static inline void empty_child_dec(struct key_vector *n)
 
 static struct key_vector *leaf_new(t_key key, struct fib_alias *fa)
 {
-	struct tnode *kv = kmem_cache_alloc(trie_leaf_kmem, GFP_KERNEL);
-	struct key_vector *l = kv->kv;
+	struct key_vector *l;
+	struct tnode *kv;
 
+	kv = kmem_cache_alloc(trie_leaf_kmem, GFP_KERNEL);
 	if (!kv)
 		return NULL;
 
 	/* initialize key vector */
+	l = kv->kv;
 	l->key = key;
 	l->pos = 0;
 	l->bits = 0;
@@ -346,24 +348,26 @@ static struct key_vector *leaf_new(t_key key, struct fib_alias *fa)
 
 static struct key_vector *tnode_new(t_key key, int pos, int bits)
 {
-	struct tnode *tnode = tnode_alloc(bits);
 	unsigned int shift = pos + bits;
-	struct key_vector *tn = tnode->kv;
+	struct key_vector *tn;
+	struct tnode *tnode;
 
 	/* verify bits and pos their msb bits clear and values are valid */
 	BUG_ON(!bits || (shift > KEYLENGTH));
 
-	pr_debug("AT %p s=%zu %zu\n", tnode, TNODE_SIZE(0),
-		 sizeof(struct key_vector *) << bits);
-
+	tnode = tnode_alloc(bits);
 	if (!tnode)
 		return NULL;
 
+	pr_debug("AT %p s=%zu %zu\n", tnode, TNODE_SIZE(0),
+		 sizeof(struct key_vector *) << bits);
+
 	if (bits == KEYLENGTH)
 		tnode->full_children = 1;
 	else
 		tnode->empty_children = 1ul << bits;
 
+	tn = tnode->kv;
 	tn->key = (shift < KEYLENGTH) ? (key >> shift) << shift : 0;
 	tn->pos = pos;
 	tn->bits = bits;
@@ -2054,11 +2058,12 @@ static struct key_vector *fib_trie_get_next(struct fib_trie_iter *iter)
 static struct key_vector *fib_trie_get_first(struct fib_trie_iter *iter,
 					     struct trie *t)
 {
-	struct key_vector *n, *pn = t->kv;
+	struct key_vector *n, *pn;
 
 	if (!t)
 		return NULL;
 
+	pn = t->kv;
 	n = rcu_dereference(pn->tnode[0]);
 	if (!n)
 		return NULL;
-- 
2.4.2

Re: [PATCH] fib_trie: coding style: Use pointer after check

[David Miller]

From: Firo Yang <firogm@gmail.com>
Date: Mon,  8 Jun 2015 11:54:51 +0800

> As Alexander Duyck pointed out that:
> struct tnode {
>         ...
>         struct key_vector kv[1];
> }
> The kv[1] member of struct tnode is an arry that refernced by
> a null pointer will not crash the system, like this:
> struct tnode *p = NULL;
> struct key_vector *kv = p->kv;
> As such p->kv doesn't actually dereference anything, it is simply a
> means for getting the offset to the array from the pointer p.
> 
> This patch make the code more regular to avoid making people feel
> odd when they look at the code.
> 
> Signed-off-by: Firo Yang <firogm@gmail.com>

Applied.

Re: [PATCH] fib_trie: coding style: Use pointer after check

[David Miller]

From: Firo Yang <firogm@gmail.com>
Date: Mon,  8 Jun 2015 11:54:51 +0800

> As Alexander Duyck pointed out that:
> struct tnode {
>         ...
>         struct key_vector kv[1];
> }
> The kv[1] member of struct tnode is an arry that refernced by
> a null pointer will not crash the system, like this:
> struct tnode *p = NULL;
> struct key_vector *kv = p->kv;
> As such p->kv doesn't actually dereference anything, it is simply a
> means for getting the offset to the array from the pointer p.
> 
> This patch make the code more regular to avoid making people feel
> odd when they look at the code.
> 
> Signed-off-by: Firo Yang <firogm@gmail.com>

Applied.