Nonblocking test
setup a c program to fill up the pipe of /dev/pts/$any num
```
$ cc -o nonblocking nonblocking.c
$ ./nonblocking
$ make
$ ktrace ./wall-test msg
$ kdump -f ktrace.out
```
normal test
$ make
$ ktrace ./wall-test msg
$ kdump -f ktrace.out
Set up enotcapable to get coredump
$ sysctl kern.trap_enotcap=1
$ sysctl kern.corefile= /tmp/coredumps/%N.core
$ gdb executable corefile