netdev - Re: [RFC] Zero-length write() does not generate a datagram on connected socket

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Date:	Wed, 26 Sep 2007 11:18:39 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	shemminger@...ux-foundation.org (Stephen Hemminger)
Cc:	netdev@...r.kernel.org
Subject: Re: [RFC] Zero-length write() does not generate a datagram on connected socket

Stephen Hemminger <shemminger@...ux-foundation.org> wrote:
> The bug http://bugzilla.kernel.org/show_bug.cgi?id=5731
> describes an issue where write() can't be used to generate a zero-length
> datagram (but send, and sendto do work).
> 
> I think the following is needed:
> 
> --- a/net/socket.c      2007-08-20 09:54:28.000000000 -0700
> +++ b/net/socket.c      2007-09-24 15:31:25.000000000 -0700
> @@ -777,8 +777,11 @@ static ssize_t sock_aio_write(struct kio
>        if (pos != 0)
>                return -ESPIPE;
> 
> -       if (iocb->ki_left == 0) /* Match SYS5 behaviour */
> -               return 0;
> +       if (unlikely(iocb->ki_left == 0)) {
> +               struct socket *sock = iocb->ki_filp->private_data;
> +               if (sock->type == SOCK_STREAM)
> +                       return 0;
> +       }

I'm not sure whether all STREAM protocols treat zero-length
sends as no-ops.  What about SCTP?

Put it another way, do we really need to keep the short-circuit
for SOCK_STREAM?

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
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