Re: [PATCH] /dev/epoll update ...

[Dan Kegel <dank@kegel.com>]

Davide Libenzi wrote:
> 1)      if (recv()/send() == FAIL)
> 2)              ioctl(EP_POLL);

A lot of people, including me, were under the mistaken impression
that /dev/epoll, like /dev/poll, provided an efficient way to
retrieve the current readiness state of fd's.  I understand from your post
that /dev/epoll's purpose is to retrieve state changes; in other
words, it's exactly like F_SETSIG/F_SETOWN/O_ASYNC except that
the readiness change indications are picked up via an ioctl
rather than via a signal.

A scorecard for the confused (Davide, correct me if I'm wrong):

* API's that allow you to retrieve the current readiness state of
  a set of fd's:  poll(), select(), /dev/poll, kqueue().
  Buzzwords describing this kind of interface: level-triggered, multishot.

* API's that allow you to retrieve *changes* to the readiness state of
  a set of fd's: F_SETSIG/F_SETOWN/O_ASYNC + sigtimedwait(), /dev/epoll, kqueue().
  Buzzwords describing this kind of interface: edge-triggered, single-shot.

(Note that kqueue is in both camps.)

Er, I guess that means I'll rip up the /dev/epoll support I based on my
/dev/poll code, and replace it with some based on my O_ASYNC code...

- Dan