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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: David Ahern <dsahern@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
David Ahern 2018-05-21 09:08:13 -07:00 committed by Daniel Borkmann
parent fd0bfa8d6e
commit 50d889b178
2 changed files with 33 additions and 0 deletions
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2
include/net/ip_fib.h
View File

@ -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 */

31
net/ipv4/route.c
View File

@ -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)
{