kern/170203: [kern] piped dd' s don' t behave sanely when dealing with a fifo

[Bruce Evans]

On Sun, 29 Jul 2012, David Xu wrote:

>> I have just written two quick-and-dirty test cases:
>> 
>> http://people.freebsd.org/~davidxu/patch/fifopipe/fifo_selectread.c
>> http://people.freebsd.org/~davidxu/patch/fifopipe/fifo_selectwrite.c
>> 
>> without patch for kernel code,  a child process will print out "timeout".

> I have updated patch, the patch fixed lost-notification bug for select():
> http://people.freebsd.org/~davidxu/patch/fifopipe/kernel_pipe2.diff

So it was a bug in the new pipe code.

The test seemed to work under FreeBSD-~5.2 but was hard to configure.
It gave lots of abort traps.  One was for the big buffer.  This is too
big for -current too, and causes a mysterious abort trap with no core,
before exec.  truss, gdb and bde were confused.

Bruce