net: add NETDEV_PRECHANGEMTU to notify before mtu change happens (1d486bfb) · Commits · 戴 / test

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>

include/linux/netdevice.h

+2 −1

Original line number	Diff line number	Diff line
		@@ -1718,7 +1718,7 @@ struct pcpu_sw_netstats {
		#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 @@ struct pcpu_sw_netstats {
		#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);

net/core/dev.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -5392,6 +5392,11 @@ int dev_set_mtu(struct net_device *dev, int new_mtu)
		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);

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