[Bug 95331] fcntl.2 + sigaction.2 + signal.7 need further information about use of a SA_SIGINFO signal handler that uses si->si_fd

https://bugzilla.kernel.org/show_bug.cgi?id=95331

--- Comment #1 from Jason Vas Dias <jason.vas.dias-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> ---

To test (under kernel 3.13, Linux x86_64 8-core)

   $ gcc -g -pthread -o t_sigio_rdwr  t_sigio_rdwr.c
   $ mkfifo -m 0600 /tmp/f.in /tmp/f.out
   $ strace -f bash -c './t_sigio_rdwr </tmp/f.in >/tmp/f.out' &
   ...
   $ echo 'hello' >/tmp/f.in && read res </tmp/f.out && echo "RES: $res"
   RES: hello
   ...
   $ echo 'hel2o' >/tmp/f.in 
   ...
   $ read res </tmp/f.out && echo "RES: $res"
   ^C
   ^- now you have to press <CTRL+C>, at which time the t_sigio_rdwr
      process does get a SIGIO with si->si_fd == 1, but it is now too late -
      the reader has disconnected.

Can anyone answer the question:
  For output (O_WRONLY|O_ASYNC) file descriptors, WHEN is the F_SETOWN signal 
  or SIGIO meant to be sent ? Is it upon connection of a new reader FD to the
  read end of the the pipe, or when a reader FD is closed, or both ? 
  IMHO, it must be possible to trigger the first case (sent on connection of
new 
  reader) but I can't see how to do it - the process only gets a SIGIO when a
  reader disconnects.

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