net/sched: cls_api: Expose tc block to the datapath

The datapath can now find the block of the port in which the packet arrived
at.

In the next patch we show a possible usage of this patch in a new
version of mirred that multicasts to all ports except for the port in
which the packet arrived on.
Co-developed-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Co-developed-by: Pedro Tammela <pctammela@mojatatu.com>
Signed-off-by: Pedro Tammela <pctammela@mojatatu.com>
Signed-off-by: Victor Nogueira <victor@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sch_generic.h

@@ -484,6 +484,8 @@ struct tcf_block {
 	struct mutex proto_destroy_lock; /* Lock for proto_destroy hashtable. */
 };
 
+struct tcf_block *tcf_block_lookup(struct net *net, u32 block_index);
+
 static inline bool lockdep_tcf_chain_is_locked(struct tcf_chain *chain)
 {
 	return lockdep_is_held(&chain->filter_chain_lock);

net/sched/cls_api.c

@@ -1011,12 +1011,13 @@ static struct tcf_block *tcf_block_create(struct net *net, struct Qdisc *q,
 	return block;
 }
 
-static struct tcf_block *tcf_block_lookup(struct net *net, u32 block_index)
+struct tcf_block *tcf_block_lookup(struct net *net, u32 block_index)
 {
 	struct tcf_net *tn = net_generic(net, tcf_net_id);
 
 	return idr_find(&tn->idr, block_index);
 }
+EXPORT_SYMBOL(tcf_block_lookup);
 
 static struct tcf_block *tcf_block_refcnt_get(struct net *net, u32 block_index)
 {