net.inet.udp.log_in_vain strange syslog reports

[Eric van Gyzen]

On 02/15/2017 08:56, Mark Martinec wrote:
> In a similar vein, I noticed also the following in our logs,
> with net.inet.tcp.log_in_vain=1.
>
> Looks like messages got concatenated somehow:
>
> Jan 25 01:37:53 mildred kernel: TCP: [2607:ff10:c5:509a::10]:26459 to
> [2001:1470:ff80::80:16]:4911 tcpflags 0x2<SYN>; tcp_input: Connection attempt to
> closed TCP: [2607:ff10:c5:509a::10]:14898 to [2001:1470:ff80::80:16]:5222
> tcpflags 0x2<SYN>; tcp_input: Connection attempt to closed port

The length of the truncated "TCP:...closed" message is just under 128, which is 
the PRINTF_BUFR_SIZE as defined in sys/amd64/conf/GENERIC.  You could try 
increasing this value and rebuilding your kernel to see if that fixes the 
truncation.  Don't increase it very much, since it's used to declare a buffer on 
the stack, and stack space is quite limited.  For this case, 180 should be enough.

Eric