[NET]: dev_mcast: add multicast list synchronization helpers

The method drivers currently use to synchronize multicast lists is not
very pretty:

- walk the multicast list
- search each entry on a copy of the previous list
- if new add to lower device
- walk the copy of the previous list
- search each entry on the current list
- if removed delete from lower device
- copy entire list

This patch adds a new field to struct dev_addr_list to store the
synchronization state and adds two helper functions for synchronization
and cleanup.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 78 insertions, 0 deletions

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index f193aba30384..e5af458ab04b 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -190,6 +190,7 @@ struct dev_addr_list
         struct dev_addr_list    *next;
         u8                      da_addr[MAX_ADDR_LEN];
         u8                      da_addrlen;
+        u8                      da_synced;
         int                     da_users;
         int                     da_gusers;
 };
@@ -1103,6 +1104,8 @@ extern int		dev_unicast_delete(struct net_device *dev, void *addr, int alen);
 extern int              dev_unicast_add(struct net_device *dev, void *addr, int alen);
 extern int              dev_mc_delete(struct net_device *dev, void *addr, int alen, int all);
 extern int              dev_mc_add(struct net_device *dev, void *addr, int alen, int newonly);
+extern int              dev_mc_sync(struct net_device *to, struct net_device *from);
+extern void             dev_mc_unsync(struct net_device *to, struct net_device *from);
 extern void             dev_mc_discard(struct net_device *dev);
 extern int              __dev_addr_delete(struct dev_addr_list **list, int *count, void *addr, int alen, int all);
 extern int              __dev_addr_add(struct dev_addr_list **list, int *count, void *addr, int alen, int newonly);
diff --git a/net/core/dev_mcast.c b/net/core/dev_mcast.c
index aa38100601fb..235a2a8a0d05 100644
--- a/net/core/dev_mcast.c
+++ b/net/core/dev_mcast.c
@@ -102,6 +102,81 @@ int dev_mc_add(struct net_device *dev, void *addr, int alen, int glbl)
         return err;
 }
 
+/**
+ *      dev_mc_sync     - Synchronize device's multicast list to another device
+ *      @to: destination device
+ *      @from: source device
+ *
+ *      Add newly added addresses to the destination device and release
+ *      addresses that have no users left. The source device must be
+ *      locked by netif_tx_lock_bh.
+ *
+ *      This function is intended to be called from the dev->set_multicast_list
+ *      function of layered software devices.
+ */
+int dev_mc_sync(struct net_device *to, struct net_device *from)
+{
+        struct dev_addr_list *da;
+        int err = 0;
+
+        netif_tx_lock_bh(to);
+        for (da = from->mc_list; da != NULL; da = da->next) {
+                if (!da->da_synced) {
+                        err = __dev_addr_add(&to->mc_list, &to->mc_count,
+                                             da->da_addr, da->da_addrlen, 0);
+                        if (err < 0)
+                                break;
+                        da->da_synced = 1;
+                        da->da_users++;
+                } else if (da->da_users == 1) {
+                        __dev_addr_delete(&to->mc_list, &to->mc_count,
+                                          da->da_addr, da->da_addrlen, 0);
+                        __dev_addr_delete(&from->mc_list, &from->mc_count,
+                                          da->da_addr, da->da_addrlen, 0);
+                }
+        }
+        if (!err)
+                __dev_set_rx_mode(to);
+        netif_tx_unlock_bh(to);
+
+        return err;
+}
+EXPORT_SYMBOL(dev_mc_sync);
+
+
+/**
+ *      dev_mc_unsync   - Remove synchronized addresses from the destination
+ *                        device
+ *      @to: destination device
+ *      @from: source device
+ *
+ *      Remove all addresses that were added to the destination device by
+ *      dev_mc_sync(). This function is intended to be called from the
+ *      dev->stop function of layered software devices.
+ */
+void dev_mc_unsync(struct net_device *to, struct net_device *from)
+{
+        struct dev_addr_list *da;
+
+        netif_tx_lock_bh(from);
+        netif_tx_lock_bh(to);
+
+        for (da = from->mc_list; da != NULL; da = da->next) {
+                if (!da->da_synced)
+                        continue;
+                __dev_addr_delete(&to->mc_list, &to->mc_count,
+                                  da->da_addr, da->da_addrlen, 0);
+                da->da_synced = 0;
+                __dev_addr_delete(&from->mc_list, &from->mc_count,
+                                  da->da_addr, da->da_addrlen, 0);
+        }
+        __dev_set_rx_mode(to);
+
+        netif_tx_unlock_bh(to);
+        netif_tx_unlock_bh(from);
+}
+EXPORT_SYMBOL(dev_mc_unsync);
+
 /*
  *      Discard multicast list when a device is downed
  */