[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

Jason Vas Dias [off-list ref] changed:

           What    |Removed                     |Added
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 Attachment #171961|0                           |1
        is obsolete|                            |

--- Comment #4 from Jason Vas Dias <jason.vas.dias-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> ---

Created attachment 171971
  --> https://bugzilla.kernel.org/attachment.cgi?id=171971&action=edit
better version

Now, if you run:

  $ ./t_sigio_rdwr_gsf </tmp/f.in >/tmp/f.out &
  $ echo 'hello' >/tmp/f.in && read res </tmp/f.out && echo "RES: $res"
  RES: hello
  $ ps -ef | grep t_sigio 
    # ie. get the pid of the t_sigio_rdwr_gsf process in $TS_PID
  $ echo hel2o >/tmp/f.in
  $ kill -IO $TS_PID; read res </tmp/f.out && echo 'RES: '"$res"
  RES: hel2o

But if you do not do 'kill -IO $TS_PID;' and just do ' read res </tmp/f.out ',
after sending the second 'hel2o' line, the reader will hang, because the
t_sigio_rdwr process gets NO SIGNALs at all after the SIGPIPE attempting to 
write, until the reader disconnects.  I think this might be a kernel bug
in the way it is generating siginfo events for output pipes - or is it 
a documentation bug ? Because even the short one line description of SIGIO
states : 'I/O now possible' - yet for writable pipe FDs, linux is generating
SIGIO only when output becomes IMpossible on the FD - why is this ?

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