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From: Jogchem de Groot <bighawk@kryptology.org>
To: linux-kernel@vger.kernel.org
Subject: Re: poll() incompatability with POSIX.1-2001
Date: Mon, 14 Oct 2002 19:13:43 +0200
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Hello, 

This is a failure to connect! The socket is therefore not ready for
writing  or reading -ever. This behavior may not be correct, not
because of a failure to set the POLLOUT bit, but because the POLLIN
bit is set. Check if this is really true. I can't duplicate this
on 2.4.18 here because it's hard to get a deferred connect with my
setup.

It's really true:..

Here is some strace output:

Case where connect() succeeds:

connect(3, {sin_family=AF_INET, sin_port=htons(111), 
sin_addr=inet_addr("127.0.0.1")}}, 16) = -1 EINPROGRESS (Operation now in 
progress)
poll([{fd=3, events=POLLIN|POLLOUT, revents=POLLOUT}], 1, -1) = 1
getsockopt(3, SOL_SOCKET, SO_ERROR, [0], [4]) = 0

As you can see SO_ERROR returns '0', connection succeeded.

Case where connect() fails:

connect(3, {sin_family=AF_INET, sin_port=htons(110), 
sin_addr=inet_addr("127.0.0.1")}}, 16) = -1 EINPROGRESS (Operation now in 
progress)
poll([{fd=3, events=POLLIN|POLLOUT, revents=POLLIN|POLLERR|POLLHUP}], 1, -1) 
= 1
getsockopt(3, SOL_SOCKET, SO_ERROR, [111], [4]) = 0

As you can see SO_ERROR returns '111', connection failed.

   bighawk