net: add NETDEV_PRECHANGEMTU to notify before mtu change happens
Currently, if a device changes its mtu, first the change happens (invloving
all the side effects), and after that the NETDEV_CHANGEMTU is sent so that
other devices can catch up with the new mtu. However, if they return
NOTIFY_BAD, then the change is reverted and error returned.
This is a really long and costy operation (sometimes). To fix this, add
NETDEV_PRECHANGEMTU notification which is called prior to any change
actually happening, and if any callee returns NOTIFY_BAD - the change is
aborted. This way we're skipping all the playing with apply/revert the mtu.
CC: "David S. Miller" <davem@davemloft.net>
CC: Jiri Pirko <jiri@resnulli.us>
CC: Eric Dumazet <edumazet@google.com>
CC: Nicolas Dichtel <nicolas.dichtel@6wind.com>
CC: Cong Wang <amwang@redhat.com>
Signed-off-by: Veaceslav Falico <vfalico@redhat.com>
Acked-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 30f6513..d7668b88 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1718,7 +1718,7 @@
#define NETDEV_CHANGE 0x0004 /* Notify device state change */
#define NETDEV_REGISTER 0x0005
#define NETDEV_UNREGISTER 0x0006
-#define NETDEV_CHANGEMTU 0x0007
+#define NETDEV_CHANGEMTU 0x0007 /* notify after mtu change happened */
#define NETDEV_CHANGEADDR 0x0008
#define NETDEV_GOING_DOWN 0x0009
#define NETDEV_CHANGENAME 0x000A
@@ -1734,6 +1734,7 @@
#define NETDEV_JOIN 0x0014
#define NETDEV_CHANGEUPPER 0x0015
#define NETDEV_RESEND_IGMP 0x0016
+#define NETDEV_PRECHANGEMTU 0x0017 /* notify before mtu change happened */
int register_netdevice_notifier(struct notifier_block *nb);
int unregister_netdevice_notifier(struct notifier_block *nb);