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Commit 50d889b1 authored by David Ahern's avatar David Ahern Committed by Daniel Borkmann
Browse files

net/ipv4: Add helper to return path MTU based on fib result 



Determine path MTU from a FIB lookup result. Logic is a distillation of
ip_dst_mtu_maybe_forward.

Signed-off-by: default avatarDavid Ahern <dsahern@gmail.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent fd0bfa8d

include/net/ip_fib.h

+2 −0
Original line number Diff line number Diff line
@@ -449,4 +449,6 @@ static inline void fib_proc_exit(struct net *net) 
}

#endif



u32 ip_mtu_from_fib_result(struct fib_result *res, __be32 daddr);



#endif  /* _NET_FIB_H */

net/ipv4/route.c

+31 −0
Original line number Diff line number Diff line
@@ -1352,6 +1352,37 @@ static struct fib_nh_exception *find_exception(struct fib_nh *nh, __be32 daddr) 
	return NULL;

}



/* MTU selection:

 * 1. mtu on route is locked - use it

 * 2. mtu from nexthop exception

 * 3. mtu from egress device

 */



u32 ip_mtu_from_fib_result(struct fib_result *res, __be32 daddr)

{

	struct fib_info *fi = res->fi;

	struct fib_nh *nh = &fi->fib_nh[res->nh_sel];

	struct net_device *dev = nh->nh_dev;

	u32 mtu = 0;



	if (dev_net(dev)->ipv4.sysctl_ip_fwd_use_pmtu ||

	    fi->fib_metrics->metrics[RTAX_LOCK - 1] & (1 << RTAX_MTU))

		mtu = fi->fib_mtu;



	if (likely(!mtu)) {

		struct fib_nh_exception *fnhe;



		fnhe = find_exception(nh, daddr);

		if (fnhe && !time_after_eq(jiffies, fnhe->fnhe_expires))

			mtu = fnhe->fnhe_pmtu;

	}



	if (likely(!mtu))

		mtu = min(READ_ONCE(dev->mtu), IP_MAX_MTU);



	return mtu - lwtunnel_headroom(nh->nh_lwtstate, mtu);

}



static bool rt_bind_exception(struct rtable *rt, struct fib_nh_exception *fnhe,

			      __be32 daddr, const bool do_cache)

{