linux-kernel - Re: unexpected extra pollout events from epoll

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Date:	Sun, 26 Oct 2008 17:58:49 -0700 (PDT)
From:	Paul P <ppak_98@...oo.com>
To:	linux-kernel@...r.kernel.org
Subject: Re: unexpected extra pollout events from epoll

> You do that by writing data until it's finished, or you
> get EAGAIN. If you
> get EAGAIN, you listen for EPOLLOUT.
> Reading is same, but you'd wait for EPOLLIN.

I've got a few questions about this approach.  The most logical 
way to do this seems to be:

1) Leave the epoll_wait with the EPOLLIN|EPOLLOUT event flags and
 use epoll_ctl to switch the interest mask for each fd between EPOLLIN 
and EPOLLOUT on a per fd basis.

2) When I'm ready to write, I do a write and if it does not fully 
write and I get the EAGAIN flag, I switch the fd with epoll_ctl(fd,MOD,EPOLLOUT). 

However, I get strange behavior when I tried adding fd's with only the 
EPOLLIN interest mask. If I use epoll_wait with both the EPOLLIN and 
EPOLLOUT interest mask, but add fd's with only the EPOLLIN interest mask,
I still seem to get EPOLLOUT events on the fd.

Am I supposed to change the main loop with epoll_wait so that when one 
socket is reading that I switch the main loop to get EPOLLOUT events?  
That means that I'm not receiving on any fd while I'm sending, so this 
probably isn't right.

So, I'm a little confused.

Thanks in advance.

Paul

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