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>