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

[bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r@public.gmane.org]

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

--- Comment #10 from Jason Vas Dias <jason.vas.dias-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> ---
Sorry, version of above comment #8 with typos fixed:

I think linux should provide a way of by-passing this generation of error
events
for writable FDs with no readers - blocking should be possible for writable
pipe
FDs for which the "wait for readers on write" (WFROW??) fcntl or ioctl has been
issued, which would only return success for writable pipe FDs with no readers
(readers == 0) ; for such pipes, for which SIGPIPE or write has set errno to
EPIPE only once, blocking writes would then succeed,  until a new reader has
connected, upon which a SIGIO / SIGPOLL or fcntl(fd, F_SETSIG, signum)
specified 
signal with that signal being caught, would be sent if the FD had such a
handler
registered for it with the siginfo si_band and si_fd fields correctly filled
in;
such a signal would also be sent and write() would return -1 ONCE for such FDs
when the last reader disconnects, as currently happens; but if O_NONBLOCK is
NOT
set in the FD's flags, then the next write would block, instead of returning -1
as currently happens, or at least a signal would be sent if registered and the 
O_ASYNC bit is set in the FD's flags .
This would essentially fix the problem of having to know the name of the 
pipe in order to re-open it and be able to wait for readers to connect ;
one could handle a write returning -1 with EPIPE or a SIGPIPE by simply
entering pause() with a SIGIO handler registered, which is NOT currently
the case.

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