netdev - ip_no_pmtu_disc and UDP

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Date:	Fri, 23 Oct 2015 09:45:47 -0700
From:	Vincent Li <vincent.mc.li@...il.com>
To:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: ip_no_pmtu_disc and UDP

Hi,

It looks ip_no_pmtu_disc setting does not affect UDP IP packet DF bit
setting, is that intended behavior? echo 0, 1, 2, 3 respectively to
ip_no_pmtu_disc, UDP IP packet always have DF bit cleared, unless use
IP_PMTUDISC_DO on IP_MTU_DISCOVER as ip man page says.

in inet_create, seems to prove that.

       if (net->ipv4.sysctl_ip_no_pmtu_disc)
                inet->pmtudisc = IP_PMTUDISC_DONT;
        else
                inet->pmtudisc = IP_PMTUDISC_WANT;

so I am wondering why UDP is excluded by ip_no_pmtu_disc, why in
inet_create, not assign each individual ip_no_pmtu_disc setting to
inet->pmtudisc but only check true and assign IP_PMTUDISC_DONT or
IP_PMTUDISC_WANT only.

Thanks

Vincent
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