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dst: Metadata destinations

Browse source 
Introduces a new dst_metadata which enables to carry per packet metadata
between forwarding and processing elements via the skb->dst pointer.

The structure is set up to be a union. Thus, each separate type of
metadata requires its own dst instance. If demand arises to carry
multiple types of metadata concurrently, metadata dst entries can be
made stackable.

The metadata dst entry is refcnt'ed as expected for now but a non
reference counted use is possible if the reference is forced before
queueing the skb.

In order to allow allocating dsts with variable length, the existing
dst_alloc() is split into a dst_alloc() and dst_init() function. The
existing dst_init() function to initialize the subsystem is being
renamed to dst_subsys_init() to make it clear what is what.

The check before ip_route_input() is changed to ignore metadata dsts
and drop the dst inside the routing function thus allowing to interpret
metadata in a later commit.

Signed-off-by: Thomas Graf <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
This commit is contained in:
Thomas Graf 2015-07-21 10:43:56 +02:00 • committed by David S. Miller
commit f38a9eb1f7
6 changed files with 112 additions and 17 deletions
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3
net/ipv4/ip_input.c
View file

@ -146,6 +146,7 @@
#include <net/xfrm.h>
#include <linux/mroute.h>
#include <linux/netlink.h>
#include <net/dst_metadata.h>
/*
* Process Router Attention IP option (RFC 2113)
@ -331,7 +332,7 @@ static int ip_rcv_finish(struct sock *sk, struct sk_buff *skb)
* Initialise the virtual path cache for the packet. It describes
* how the packet travels inside Linux networking.
*/
if (!skb_dst(skb)) {
if (!skb_valid_dst(skb)) {
int err = ip_route_input_noref(skb, iph->daddr, iph->saddr,
iph->tos, skb->dev);
if (unlikely(err)) {

2
net/ipv4/route.c
View file

@ -1690,6 +1690,8 @@ static int ip_route_input_slow(struct sk_buff *skb, __be32 daddr, __be32 saddr,
by fib_lookup.
*/
skb_dst_drop(skb);
if (ipv4_is_multicast(saddr) || ipv4_is_lbcast(saddr))
goto martian_source;