RE: [PATCH/RFC] POLLHUP tinkering ...

[David Schwartz]

> From: Davide Libenzi <davidel@xxxxxxxxxxxxxxx>
> Date: Sun, 8 Jan 2006 16:02:10 -0800 (PST)

> > But if and hangup happened with some data (data + FIN), they won't
> > receive any more events for the Linux poll subsystem (and epoll,
> > when using the event triggered interface), so they are forced to
> > issue an extra read() after the loop to detect the EOF
> > condition. Besides from the extra read() overhead, the code does not
> > come exactly pretty.

> The extra last read is always necessary, it's an error synchronization
> barrier.  Did you know that?

	If there is an error, an error event must be returned. An edge-triggered
interface must report every event that occurs with an indication of that
type.

> If a partial read or write hits an error, the successful amount of
> bytes read or written before the error occurred is returned.  Then any
> subsequent read or write will report the error immediately.

	If the connection closes and the edge-triggered interface does not give a
HUP indication, then it is broken.

	A HUP is not a read event and signalling a read is not sufficient.

	DS


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/