[Bug 224615] [PATCH] kevent: EVFILT_READ returns EV_EOF on named pipe when it should not

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=224615

            Bug ID: 224615
           Summary: [PATCH] kevent: EVFILT_READ returns EV_EOF on named
                    pipe when it should not
           Product: Base System
           Version: CURRENT
          Hardware: Any
                OS: Any
            Status: New
          Keywords: patch
          Severity: Affects Only Me
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: jan.kokemueller at gmail.com
          Keywords: patch

Created attachment 189130
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=189130&action=edit
patch for filt_piperead

When connecting as a new reader to a named pipe after all previous writers have
disconnected, EVFILT_READ currently returns EV_EOF.

poll(2) was fixed a while ago so that it won't return POLLHUP in this case (at
least since r238936). The attached patch brings the logic in EVFILT_READ in
sync with poll(2) again.

I wonder why the other side of the pipe is also checked in EVFILT_READ.
Wouldn't it be enough to just check for EOF on the readers side? This would be
consistent with sockets for example (where just SBS_CANTRCVMORE leads to
EV_EOF).

I've also attached a small patch to the pipepoll.c regression test that can be
used to reproduce the issue.

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