A (perhaps silly) kqueue question

[Vlad GALU]

On 3/14/08, Vlad GALU <dudu at dudu.ro> wrote:
> On 3/8/08, Vlad GALU <dudu at dudu.ro> wrote:
>  > On 3/8/08, Robert Watson <rwatson at freebsd.org> wrote:
>  >  > On Fri, 7 Mar 2008, Vlad GALU wrote:
>  >  >
>  >  >
>  >  > > I see an unusual symptom with one of our in-house applications. The main I/O
>  >  >  > loop calls kevent(), which in turn returns two events with EV_EOF error set,
>  >  >  > always for the same descriptors (they're both socket descriptors). As the
>  >  >  > man page is not pretty clear about it and I don't have my UNP copy at hand,
>  >  >  > I would like to ask the list whether the error events are supposed to be
>  >  >  > one-shot or not.
>  >  >
>  >  >
>  >  > I wonder if it's returning one event for the read socket buffer, and one event
>  >  >  for the write socket buffer, since there are really two event sources for each
>  >  >  socket?  Not that this is desirable behavior, but it might explain it.  If you
>  >  >  shutdown() only read, do you get back one EOF kevent and one writable kevent?
>  >
>  >
>  >    I'll try that and see. The only issue being the low frequency this
>  >  symptom appears at. I'll get back to the list once I have more info.
>
>
>     Haven't gotten to the point of testing shutdown() behavior, but
>  here's a truss excerpt of the symptom:
>
>  -- cut here --
>  kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
>  0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
>  kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
>  0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
>  kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
>  0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
>  kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
>  0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
>  kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
>  0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
>  kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
>  0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
>  kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
>  0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
>  kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
>  0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
>  kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
>  0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
>  kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
>  0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
>  kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
>  0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
>  kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
>  0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
>  kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
>  0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
>  kevent(3,0x0,0,{0x7,EVFILT_WRITE,EV_EOF,54,0x832c,0x800d08080
>  0x7,EVFILT_READ,EV_EOF,54,0x2a,0x800d08080},1024,0x0) = 2 (0x2)
>  -- and here --
>
>    So two EOF are returrned for descriptor 7, and errno would be
>  ECONNRESET. The question is now, why isn't it oneshot?

    Ah one more thing. When EOF is caught, a handler which forcibly
removes the event is called, but it keeps poping up again and again.

>
>
>  >
>  >
>  >  >
>  >  >  Robert N M Watson
>  >  >  Computer Laboratory
>  >  >  University of Cambridge
>  >  >
>  >
>  >
>  >
>  > --
>  >  Mahnahmahnah!
>  >
>
>
>
> --
>  Mahnahmahnah!
>


-- 
Mahnahmahnah!