net: flow_offload: add flow_block_cb_is_busy() and use it

This patch adds a function to check if flow block callback is already in
use.  Call this new function from flow_block_cb_setup_simple() and from
drivers.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 0 deletions

diff --git a/net/dsa/slave.c b/net/dsa/slave.c
index 90c32fd680db..9bcb598fc840 100644
--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c
@@ -961,6 +961,9 @@ static int dsa_slave_setup_tc_block(struct net_device *dev,
 
         switch (f->command) {
         case FLOW_BLOCK_BIND:
+                if (flow_block_cb_is_busy(cb, dev, &dsa_slave_block_cb_list))
+                        return -EBUSY;
+
                 block_cb = flow_block_cb_alloc(f->net, cb, dev, dev, NULL);
                 if (IS_ERR(block_cb))
                         return PTR_ERR(block_cb);