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Commit 4de83b88 authored by Mahesh Bandewar's avatar Mahesh Bandewar Committed by David S. Miller
Browse files

loopback: create blackhole net device similar to loopack. 



Create a blackhole net device that can be used for "dead"
dst entries instead of loopback device. This blackhole device differs
from loopback in few aspects: (a) It's not per-ns. (b)  MTU on this
device is ETH_MIN_MTU (c) The xmit function is essentially kfree_skb().
and (d) since it's not registered it won't have ifindex.

Lower MTU effectively make the device not pass the MTU check during
the route check when a dst associated with the skb is dead.

Signed-off-by: default avatarMahesh Bandewar <maheshb@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 8909783c

drivers/net/loopback.c

+67 −9
Original line number Diff line number Diff line
@@ -55,6 +55,13 @@ 
#include <net/net_namespace.h>

#include <linux/u64_stats_sync.h>



/* blackhole_netdev - a device used for dsts that are marked expired!

 * This is global device (instead of per-net-ns) since it's not needed

 * to be per-ns and gets initialized at boot time.

 */

struct net_device *blackhole_netdev;

EXPORT_SYMBOL(blackhole_netdev);



/* The higher levels take care of making this non-reentrant (it's

 * called with bh's disabled).

 */
@@ -150,12 +157,14 @@ static const struct net_device_ops loopback_ops = { 
	.ndo_set_mac_address = eth_mac_addr,

};



/* The loopback device is special. There is only one instance

 * per network namespace.

 */

static void loopback_setup(struct net_device *dev)

static void gen_lo_setup(struct net_device *dev,

			 unsigned int mtu,

			 const struct ethtool_ops *eth_ops,

			 const struct header_ops *hdr_ops,

			 const struct net_device_ops *dev_ops,

			 void (*dev_destructor)(struct net_device *dev))

{

	dev->mtu		= 64 * 1024;

	dev->mtu		= mtu;

	dev->hard_header_len	= ETH_HLEN;	/* 14	*/

	dev->min_header_len	= ETH_HLEN;	/* 14	*/

	dev->addr_len		= ETH_ALEN;	/* 6	*/
@@ -174,11 +183,20 @@ static void loopback_setup(struct net_device *dev) 
		| NETIF_F_NETNS_LOCAL

		| NETIF_F_VLAN_CHALLENGED

		| NETIF_F_LOOPBACK;

	dev->ethtool_ops	= &loopback_ethtool_ops;

	dev->header_ops		= &eth_header_ops;

	dev->netdev_ops		= &loopback_ops;

	dev->ethtool_ops	= eth_ops;

	dev->header_ops		= hdr_ops;

	dev->netdev_ops		= dev_ops;

	dev->needs_free_netdev	= true;

	dev->priv_destructor	= loopback_dev_free;

	dev->priv_destructor	= dev_destructor;

}



/* The loopback device is special. There is only one instance

 * per network namespace.

 */

static void loopback_setup(struct net_device *dev)

{

	gen_lo_setup(dev, (64 * 1024), &loopback_ethtool_ops, &eth_header_ops,

		     &loopback_ops, loopback_dev_free);

}



/* Setup and register the loopback device. */
@@ -213,3 +231,43 @@ static __net_init int loopback_net_init(struct net *net) 
struct pernet_operations __net_initdata loopback_net_ops = {

	.init = loopback_net_init,

};



/* blackhole netdevice */

static netdev_tx_t blackhole_netdev_xmit(struct sk_buff *skb,

					 struct net_device *dev)

{

	kfree_skb(skb);

	net_warn_ratelimited("%s(): Dropping skb.\n", __func__);

	return NETDEV_TX_OK;

}



static const struct net_device_ops blackhole_netdev_ops = {

	.ndo_start_xmit = blackhole_netdev_xmit,

};



/* This is a dst-dummy device used specifically for invalidated

 * DSTs and unlike loopback, this is not per-ns.

 */

static void blackhole_netdev_setup(struct net_device *dev)

{

	gen_lo_setup(dev, ETH_MIN_MTU, NULL, NULL, &blackhole_netdev_ops, NULL);

}



/* Setup and register the blackhole_netdev. */

static int __init blackhole_netdev_init(void)

{

	blackhole_netdev = alloc_netdev(0, "blackhole_dev", NET_NAME_UNKNOWN,

					blackhole_netdev_setup);

	if (!blackhole_netdev)

		return -ENOMEM;



	dev_init_scheduler(blackhole_netdev);

	dev_activate(blackhole_netdev);



	blackhole_netdev->flags |= IFF_UP | IFF_RUNNING;

	dev_net_set(blackhole_netdev, &init_net);



	return 0;

}



device_initcall(blackhole_netdev_init);

include/linux/netdevice.h

+2 −0
Original line number Diff line number Diff line
@@ -4870,4 +4870,6 @@ do { \ 
#define PTYPE_HASH_SIZE	(16)

#define PTYPE_HASH_MASK	(PTYPE_HASH_SIZE - 1)



extern struct net_device *blackhole_netdev;



#endif	/* _LINUX_NETDEVICE_H */