[PATCH net-next 0/5] Per-net and on-demand link indices (and related) v3

[PATCH net-next 0/5] Per-net and on-demand link indices (and related) v3

[Pavel Emelyanov]

Hi!

This set tries to summarize the recent discussion of making ifindices friendly
to checkpoint-restore and consists of:

1. Prepare hash function to non-unique ifindices
2. Allow for specifying the desired ifindex on net link creation
3. Make ifindex generation per-net
4. Simplify loopback device ifindex access


Changes since v2:

* The pointer hash mix routine is rewritten
* Put ifindex on struct net in a better place
* Fixed compatibility on veth peer device ifindex configuration

Changes since v1:

* Fixed a stupid mistake with a pointer bits shift
* Turned the netdev_hash_mix routine into the generic ptr_hash_mix one
* Added a comment describing why loopback index is always 1 after the patch

Thanks,
Pavel

[PATCH 1/5] net: Dont use ifindices in hash fns

[Pavel Emelyanov]

Eric noticed, that when there will be devices with equal indices, some
hash functions that use them will become less effective as they could.
Fix this in advance by mixing the net_device address into the hash value
instead of the device index.

This is true for arp and ndisc hash fns. The netlabel, can and llc ones
are also ifindex-based, but that three are init_net-only, thus will not
be affected.

Many thanks to David and Eric for the hash32_ptr implementation!

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 include/linux/hash.h |   10 ++++++++++
 include/net/arp.h    |    3 ++-
 include/net/ndisc.h  |    3 ++-
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/include/linux/hash.h b/include/linux/hash.h
index b80506b..24df9e7 100644
--- a/include/linux/hash.h
+++ b/include/linux/hash.h
@@ -67,4 +67,14 @@ static inline unsigned long hash_ptr(const void *ptr, unsigned int bits)
 {
 	return hash_long((unsigned long)ptr, bits);
 }
+
+static inline u32 hash32_ptr(const void *ptr)
+{
+	unsigned long val = (unsigned long)ptr;
+
+#if BITS_PER_LONG == 64
+	val ^= (val >> 32);
+#endif
+	return (u32)val;
+}
 #endif /* _LINUX_HASH_H */
diff --git a/include/net/arp.h b/include/net/arp.h
index 7f7df93..b630dae 100644
--- a/include/net/arp.h
+++ b/include/net/arp.h
@@ -3,6 +3,7 @@
 #define _ARP_H
 
 #include <linux/if_arp.h>
+#include <linux/hash.h>
 #include <net/neighbour.h>
 
 
@@ -10,7 +11,7 @@ extern struct neigh_table arp_tbl;
 
 static inline u32 arp_hashfn(u32 key, const struct net_device *dev, u32 hash_rnd)
 {
-	u32 val = key ^ dev->ifindex;
+	u32 val = key ^ hash32_ptr(dev);
 
 	return val * hash_rnd;
 }
diff --git a/include/net/ndisc.h b/include/net/ndisc.h
index 96a3b5c..980d263 100644
--- a/include/net/ndisc.h
+++ b/include/net/ndisc.h
@@ -49,6 +49,7 @@ enum {
 #include <linux/types.h>
 #include <linux/if_arp.h>
 #include <linux/netdevice.h>
+#include <linux/hash.h>
 
 #include <net/neighbour.h>
 
@@ -134,7 +135,7 @@ static inline u32 ndisc_hashfn(const void *pkey, const struct net_device *dev, _
 {
 	const u32 *p32 = pkey;
 
-	return (((p32[0] ^ dev->ifindex) * hash_rnd[0]) +
+	return (((p32[0] ^ hash32_ptr(dev)) * hash_rnd[0]) +
 		(p32[1] * hash_rnd[1]) +
 		(p32[2] * hash_rnd[2]) +
 		(p32[3] * hash_rnd[3]));
-- 
1.7.6.5

[PATCH 2/5] net: Allow to create links with given ifindex

[Pavel Emelyanov]

Currently the RTM_NEWLINK results in -EOPNOTSUPP if the ifinfomsg->ifi_index
is not zero. I propose to allow requesting ifindices on link creation. This
is required by the checkpoint-restore to correctly restore a net namespace
(i.e. -- a container).

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Acked-by: Eric Dumazet <edumazet@google.com>
---
 net/core/dev.c       |    7 ++++++-
 net/core/rtnetlink.c |   12 +++++++-----
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index f91abf8..3ca300d 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5579,7 +5579,12 @@ int register_netdevice(struct net_device *dev)
 		}
 	}
 
-	dev->ifindex = dev_new_index(net);
+	ret = -EBUSY;
+	if (!dev->ifindex)
+		dev->ifindex = dev_new_index(net);
+	else if (__dev_get_by_index(net, dev->ifindex))
+		goto err_uninit;
+
 	if (dev->iflink == -1)
 		dev->iflink = dev->ifindex;
 
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 2c5a0a0..1aa1456 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1812,8 +1812,6 @@ replay:
 			return -ENODEV;
 		}
 
-		if (ifm->ifi_index)
-			return -EOPNOTSUPP;
 		if (tb[IFLA_MAP] || tb[IFLA_MASTER] || tb[IFLA_PROTINFO])
 			return -EOPNOTSUPP;
 
@@ -1839,10 +1837,14 @@ replay:
 			return PTR_ERR(dest_net);
 
 		dev = rtnl_create_link(net, dest_net, ifname, ops, tb);
-
-		if (IS_ERR(dev))
+		if (IS_ERR(dev)) {
 			err = PTR_ERR(dev);
-		else if (ops->newlink)
+			goto out;
+		}
+
+		dev->ifindex = ifm->ifi_index;
+
+		if (ops->newlink)
 			err = ops->newlink(net, dev, tb, data);
 		else
 			err = register_netdevice(dev);
-- 
1.7.6.5

[PATCH 3/5] veth: Allow to create peer link with given ifindex

[Pavel Emelyanov]

The ifinfomsg is in there (thanks kaber@ for foreseeing this long time ago),
so take the given ifidex and register netdev with it.

Ben noticed, that this code path previously ignored ifmp->ifi_index and
userland could be passing in garbage. Thus it may now fail occasionally
because the value clashes with an existing interface.

To address this it's assumed that if the caller specifies the ifindex for
the veth master device, then it's aware of this possibility and should
explicitly specify (or set to 0 for auto-assignment) the peer's ifindex as
well. With this the compatibility with old tools not setting ifindex is
preserved.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
---
 drivers/net/veth.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index 5852361..e522ff7 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -348,6 +348,9 @@ static int veth_newlink(struct net *src_net, struct net_device *dev,
 	if (tbp[IFLA_ADDRESS] == NULL)
 		eth_hw_addr_random(peer);
 
+	if (ifmp && (dev->ifindex != 0))
+		peer->ifindex = ifmp->ifi_index;
+
 	err = register_netdevice(peer);
 	put_net(net);
 	net = NULL;
-- 
1.7.6.5

[PATCH 4/5] net: Make ifindex generation per-net namespace

[Pavel Emelyanov]

Strictly speaking this is only _really_ required for checkpoint-restore to
make loopback device always have the same index.

This change appears to be safe wrt "ifindex should be unique per-system"
concept, as all the ifindex usage is either already made per net namespace
of is explicitly limited with init_net only.

There are two cool side effects of this. The first one -- ifindices of
devices in container are always small, regardless of how many containers
we've started (and re-started) so far. The second one is -- we can speed
up the loopback ifidex access as shown in the next patch.

v2: Place ifindex right after dev_base_seq : avoid two holes and use the
    same cache line, dirtied in list_netdevice()/unlist_netdevice()

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Acked-by: Eric Dumazet <edumazet@google.com>
---
 include/net/net_namespace.h |    1 +
 net/core/dev.c              |    4 ++--
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index ae1cd6c..6dc3db3 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -66,6 +66,7 @@ struct net {
 	struct hlist_head 	*dev_name_head;
 	struct hlist_head	*dev_index_head;
 	unsigned int		dev_base_seq;	/* protected by rtnl_mutex */
+	int			ifindex;
 
 	/* core fib_rules */
 	struct list_head	rules_ops;
diff --git a/net/core/dev.c b/net/core/dev.c
index 3ca300d..1f06df8 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5221,12 +5221,12 @@ int dev_ioctl(struct net *net, unsigned int cmd, void __user *arg)
  */
 static int dev_new_index(struct net *net)
 {
-	static int ifindex;
+	int ifindex = net->ifindex;
 	for (;;) {
 		if (++ifindex <= 0)
 			ifindex = 1;
 		if (!__dev_get_by_index(net, ifindex))
-			return ifindex;
+			return net->ifindex = ifindex;
 	}
 }
 
-- 
1.7.6.5

[PATCH 5/5] net: Loopback ifindex is constant now

[Pavel Emelyanov]

As pointed out, there are places, that access net->loopback_dev->ifindex
and after ifindex generation is made per-net this value becomes constant
equals 1. So go ahead and introduce the LOOPBACK_IFINDEX constant and use
it where appropriate.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Acked-by: Eric Dumazet <edumazet@google.com>
---
 drivers/net/loopback.c            |    1 +
 include/net/net_namespace.h       |    7 +++++++
 net/decnet/dn_route.c             |    6 +++---
 net/ipv4/fib_frontend.c           |    2 +-
 net/ipv4/ipmr.c                   |    2 +-
 net/ipv4/netfilter/ipt_rpfilter.c |    2 +-
 net/ipv4/route.c                  |    6 +++---
 net/ipv6/route.c                  |    2 +-
 8 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/drivers/net/loopback.c b/drivers/net/loopback.c
index e2a06fd..4a075ba 100644
--- a/drivers/net/loopback.c
+++ b/drivers/net/loopback.c
@@ -197,6 +197,7 @@ static __net_init int loopback_net_init(struct net *net)
 	if (err)
 		goto out_free_netdev;
 
+	BUG_ON(dev->ifindex != LOOPBACK_IFINDEX);
 	net->loopback_dev = dev;
 	return 0;
 
diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index 6dc3db3..97e4419 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -105,6 +105,13 @@ struct net {
 	struct sock		*diag_nlsk;
 };
 
+/*
+ * ifindex generation is per-net namespace, and loopback is
+ * always the 1st device in ns (see net_dev_init), thus any
+ * loopback device should get ifindex 1
+ */
+
+#define LOOPBACK_IFINDEX	1
 
 #include <linux/seq_file_net.h>
 
diff --git a/net/decnet/dn_route.c b/net/decnet/dn_route.c
index 85a3604..c855e8d 100644
--- a/net/decnet/dn_route.c
+++ b/net/decnet/dn_route.c
@@ -961,7 +961,7 @@ static int dn_route_output_slow(struct dst_entry **pprt, const struct flowidn *o
 		.saddr = oldflp->saddr,
 		.flowidn_scope = RT_SCOPE_UNIVERSE,
 		.flowidn_mark = oldflp->flowidn_mark,
-		.flowidn_iif = init_net.loopback_dev->ifindex,
+		.flowidn_iif = LOOPBACK_IFINDEX,
 		.flowidn_oif = oldflp->flowidn_oif,
 	};
 	struct dn_route *rt = NULL;
@@ -979,7 +979,7 @@ static int dn_route_output_slow(struct dst_entry **pprt, const struct flowidn *o
 		       "dn_route_output_slow: dst=%04x src=%04x mark=%d"
 		       " iif=%d oif=%d\n", le16_to_cpu(oldflp->daddr),
 		       le16_to_cpu(oldflp->saddr),
-		       oldflp->flowidn_mark, init_net.loopback_dev->ifindex,
+		       oldflp->flowidn_mark, LOOPBACK_IFINDEX,
 		       oldflp->flowidn_oif);
 
 	/* If we have an output interface, verify its a DECnet device */
@@ -1042,7 +1042,7 @@ source_ok:
 			if (!fld.daddr)
 				goto out;
 		}
-		fld.flowidn_oif = init_net.loopback_dev->ifindex;
+		fld.flowidn_oif = LOOPBACK_IFINDEX;
 		res.type = RTN_LOCAL;
 		goto make_route;
 	}
diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index c43ae3f..7f073a3 100644
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -218,7 +218,7 @@ __be32 fib_compute_spec_dst(struct sk_buff *skb)
 	scope = RT_SCOPE_UNIVERSE;
 	if (!ipv4_is_zeronet(ip_hdr(skb)->saddr)) {
 		fl4.flowi4_oif = 0;
-		fl4.flowi4_iif = net->loopback_dev->ifindex;
+		fl4.flowi4_iif = LOOPBACK_IFINDEX;
 		fl4.daddr = ip_hdr(skb)->saddr;
 		fl4.saddr = 0;
 		fl4.flowi4_tos = RT_TOS(ip_hdr(skb)->tos);
diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 8eec8f4..3a57570 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -1798,7 +1798,7 @@ static struct mr_table *ipmr_rt_fib_lookup(struct net *net, struct sk_buff *skb)
 		.flowi4_oif = (rt_is_output_route(rt) ?
 			       skb->dev->ifindex : 0),
 		.flowi4_iif = (rt_is_output_route(rt) ?
-			       net->loopback_dev->ifindex :
+			       LOOPBACK_IFINDEX :
 			       skb->dev->ifindex),
 		.flowi4_mark = skb->mark,
 	};
diff --git a/net/ipv4/netfilter/ipt_rpfilter.c b/net/ipv4/netfilter/ipt_rpfilter.c
index 31371be..c301300 100644
--- a/net/ipv4/netfilter/ipt_rpfilter.c
+++ b/net/ipv4/netfilter/ipt_rpfilter.c
@@ -85,7 +85,7 @@ static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
 			return ipv4_is_local_multicast(iph->daddr) ^ invert;
 		flow.flowi4_iif = 0;
 	} else {
-		flow.flowi4_iif = dev_net(par->in)->loopback_dev->ifindex;
+		flow.flowi4_iif = LOOPBACK_IFINDEX;
 	}
 
 	flow.daddr = iph->saddr;
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 21ad369..c581373 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1619,7 +1619,7 @@ static int ip_route_input_slow(struct sk_buff *skb, __be32 daddr, __be32 saddr,
 
 	if (res.type == RTN_LOCAL) {
 		err = fib_validate_source(skb, saddr, daddr, tos,
-					  net->loopback_dev->ifindex,
+					  LOOPBACK_IFINDEX,
 					  dev, in_dev, &itag);
 		if (err < 0)
 			goto martian_source_keep_err;
@@ -1895,7 +1895,7 @@ struct rtable *__ip_route_output_key(struct net *net, struct flowi4 *fl4)
 
 	orig_oif = fl4->flowi4_oif;
 
-	fl4->flowi4_iif = net->loopback_dev->ifindex;
+	fl4->flowi4_iif = LOOPBACK_IFINDEX;
 	fl4->flowi4_tos = tos & IPTOS_RT_MASK;
 	fl4->flowi4_scope = ((tos & RTO_ONLINK) ?
 			 RT_SCOPE_LINK : RT_SCOPE_UNIVERSE);
@@ -1984,7 +1984,7 @@ struct rtable *__ip_route_output_key(struct net *net, struct flowi4 *fl4)
 		if (!fl4->daddr)
 			fl4->daddr = fl4->saddr = htonl(INADDR_LOOPBACK);
 		dev_out = net->loopback_dev;
-		fl4->flowi4_oif = net->loopback_dev->ifindex;
+		fl4->flowi4_oif = LOOPBACK_IFINDEX;
 		res.type = RTN_LOCAL;
 		flags |= RTCF_LOCAL;
 		goto make_route;
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 8e80fd2..0ddf2d1 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -965,7 +965,7 @@ struct dst_entry * ip6_route_output(struct net *net, const struct sock *sk,
 {
 	int flags = 0;
 
-	fl6->flowi6_iif = net->loopback_dev->ifindex;
+	fl6->flowi6_iif = LOOPBACK_IFINDEX;
 
 	if ((sk && sk->sk_bound_dev_if) || rt6_need_strict(&fl6->daddr))
 		flags |= RT6_LOOKUP_F_IFACE;
-- 
1.7.6.5

Re: [PATCH net-next 0/5] Per-net and on-demand link indices (and related) v3

[David Miller]

From: Pavel Emelyanov <xemul@parallels.com>
Date: Thu, 09 Aug 2012 11:52:00 +0400

> This set tries to summarize the recent discussion of making ifindices friendly
> to checkpoint-restore and consists of:
> 
> 1. Prepare hash function to non-unique ifindices
> 2. Allow for specifying the desired ifindex on net link creation
> 3. Make ifindex generation per-net
> 4. Simplify loopback device ifindex access

Looks good, all applied to net-next, thanks.