Re: POLLRDONCE optimisation for epoll users (was: epoll and half closed TCP connections)

Jamie Lokier (
Mon, 14 Jul 2003 04:16:14 +0100

Davide Libenzi wrote:
> > > Where this will break by using a POLLRDHUP ?
> >
> > It will break if
> >
> > (a) fd isn't a socket
> > (b) fd isn't a TCP socket
> > (c) kernel version <= 2.5.75
> > (d) SO_RCVLOWAT < s
> > (e) there is urgent data with OOBINLINE (I think)

> Jamie, did you smoke that stuff again ? :)
> With Eric patch in the proper places it is just fine. You just make
> f_op->poll() to report the extra flag other that POLLIN. What's the problem ?

The problem in cases (a)-(e) is your loop will call read() just once
when it needs to call read() until it sees EAGAIN.

What's wrong is the behaviour of your program when the extra flag
_isn't_ set.

-- Jamie
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