linux-kernel - Re: Honoring SO_RCVLOWAT in proto

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Message-ID: <20081020035819.GG2811@fc6222126.aspadmin.net>
Date:	Sun, 19 Oct 2008 22:58:19 -0500
From:	swivel@...lls.gnugeneration.com
To:	David Miller <davem@...emloft.net>
Cc:	alan@...rguk.ukuu.org.uk, linux-kernel@...r.kernel.org
Subject: Re: Honoring SO_RCVLOWAT in proto_ops.poll methods

On Mon, Oct 13, 2008 at 02:58:16AM -0700, David Miller wrote:
> From: swivel@...lls.gnugeneration.com
> Date: Mon, 13 Oct 2008 03:32:14 -0500
> 
> > I'm using the pseudo-blocking recv() behavior achieved with SO_RCVTIMEO.
> > Thus my app expects recv() to block until SO_RCVLOWAT is met or SO_RCVTIMEO
> > expired.
> 
> But if you poll() properly, you'll never call recv() unless the amount
> of bytes you want are there.
> 
> And since I fixed poll()'s handling of SO_RCVLOWAT it should mostly
> work.

The app already has a kludge in place to work around the current kernel
with broken poll() and recv() with regards to SO_RCVLOWAT.

It's less than ideal but 'mostly works', so I'm already at that point...
Doesn't really make sense to me to rewrite the kludge to depend on a
very modern kernel without even having it be able to use recv()
properly.

I just hope we can have recv() block with MSG_PEEK when SO_RCVLOWAT is
>1 in the near future.  My goal was next time I get around to doing a
dist-upgrade the new kernel would have both poll and recv fixed and I
could disable the kludge.

>From what I can see the recv() MSG_PEEK fix is trivial anyways, why not
fix it?

Thanks,
Vito Caputo
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