DomainKey-Signature: a=rsa-sha1; c=nofws;
        s=beta; d=gmail.com;
        h=received:message-id:date:from:reply-to:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:references;
        b=aWUuTZ4wjzZhhxyn70dnRZQLbcr7Gwi91+OaUXRCflfV6OAGQyXTt1stg+fvLm9CC380o82RbVfe0TTnxPm+vZnpM9zLjuzLqznQeMsfTfjPpKUnO58M43KNHjwAgmrCWSAbrnbRUbngQKFqloK22MRr38ZON1fncms/3hnSfLc
Message-ID: <5d6b657504101712336468303c@mail.gmail.com>
Date: Sun, 17 Oct 2004 21:33:27 +0200
From: Buddy Lucas <buddy.lucas@gmail.com>
Reply-To: Buddy Lucas <buddy.lucas@gmail.com>
To: Martijn Sipkema <martijn@entmoot.nl>
Subject: Re: UDP recvmsg blocks after select(), 2.6 bug?
Cc: Lars Marowsky-Bree <lmb@suse.de>, David Schwartz <davids@webmaster.com>,
       "Linux-Kernel@Vger. Kernel. Org" <linux-kernel@vger.kernel.org>
In-Reply-To: <002b01c4b483$b2bef130$161b14ac@boromir>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
References: <20041016062512.GA17971@mark.mielke.cc>
	 <MDEHLPKNGKAHNMBLJOLKMEONPAAA.davids@webmaster.com>
	 <20041017133537.GL7468@marowsky-bree.de>
	 <5d6b657504101707175aab0fcb@mail.gmail.com>
	 <20041017150509.GC10280@mark.mielke.cc>
	 <5d6b65750410170840c80c314@mail.gmail.com>
	 <000801c4b46f$b62034b0$161b14ac@boromir>
	 <5d6b65750410171033d9d83ab@mail.gmail.com>
	 <002b01c4b483$b2bef130$161b14ac@boromir>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1530
Lines: 40

On Sun, 17 Oct 2004 20:58:39 +0100, Martijn Sipkema <martijn@entmoot.nl> wrote:
> >
> > But then I am one of those who thinks it's sane to check for
> > EWOULDBLOCK on a nonblocking socket after blocking in select().
> 
> A POSIX comliant implementation would never do this.

Here's your own quote, from a couple of hundred mails ago:

> According to POSIX:

> A descriptor shall be considered ready for reading when a call to an
>  input function with O_NONBLOCK clear would not block, whether or not
>  the function would transfer data successfully.

You concluded from this that, if select() says a descriptor is
readable, the subsequent recvmsg() must not block. The point is, from
your quote I cannot deduct anything but: a recvmsg() on a descriptor
that is readable must not block -- which makes perfect sense.

But unless POSIX also says something about the conservability of
"readability" of descriptors, specifically in between select() and
recvmsg(), your conclusion is just wrong.

> > Let's just document this and move on to something more important.
> 
> It actually _is_ important. Just implement select() and recvmsg() as
> described in the standard.

I am very glad Linux makes sane decisions while trying to adhere to
the standards as much as possible.


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