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/net/core/dev.c b/net/core/dev.c
index b2c1869..f87bedd 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5392,6 +5392,11 @@
if (!netif_device_present(dev))
return -ENODEV;
+ err = call_netdevice_notifiers(NETDEV_PRECHANGEMTU, dev);
+ err = notifier_to_errno(err);
+ if (err)
+ return err;
+
orig_mtu = dev->mtu;
err = __dev_set_mtu(dev, new_mtu);