[PATCH] rcu: avoid passing an argument to the callback function

From: Dipankar Sarma <dipankar@in.ibm.com>

This patch changes the call_rcu() API and avoids passing an argument to the
callback function as suggested by Rusty.  Instead, it is assumed that the
user has embedded the rcu head into a structure that is useful in the
callback and the rcu_head pointer is passed to the callback.  The callback
can use container_of() to get the pointer to its structure and work with
it.  Together with the rcu-singly-link patch, it reduces the rcu_head size
by 50%.  Considering that we use these in things like struct dentry and
struct dst_entry, this is good savings in space.

An example :

struct my_struct {
	struct rcu_head rcu;
	int x;
	int y;
};

void my_rcu_callback(struct rcu_head *head)
{
	struct my_struct *p = container_of(head, struct my_struct, rcu);
	free(p);
}

void my_delete(struct my_struct *p)
{
	...
	call_rcu(&p->rcu, my_rcu_callback);
	...
}

Signed-Off-By: Dipankar Sarma <dipankar@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/security/selinux/netif.c b/security/selinux/netif.c
index 4cbf8f259d93be..d23bd7e6345e5d 100644
--- a/security/selinux/netif.c
+++ b/security/selinux/netif.c
@@ -134,9 +134,9 @@ out:
 	return netif;
 }
 
-static void sel_netif_free(void *p)
+static void sel_netif_free(struct rcu_head *p)
 {
-	struct sel_netif *netif = p;
+	struct sel_netif *netif = container_of(p, struct sel_netif, rcu_head);
 	
 	DEBUGP("%s: %s\n", __FUNCTION__, netif->nsec.dev->name);
 	kfree(netif);
@@ -151,7 +151,7 @@ static void sel_netif_destroy(struct sel_netif *netif)
 	sel_netif_total--;
 	spin_unlock_bh(&sel_netif_lock);
 
-	call_rcu(&netif->rcu_head, sel_netif_free, netif);
+	call_rcu(&netif->rcu_head, sel_netif_free);
 }
 
 void sel_netif_put(struct sel_netif *netif)