From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vlad Yasevich Subject: Re: [RFC] Zero-length write() does not generate a datagram on connected socket Date: Wed, 26 Sep 2007 14:47:18 -0400 Message-ID: <46FAA936.6040205@hp.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Stephen Hemminger , netdev@vger.kernel.org To: Herbert Xu Return-path: Received: from atlrel7.hp.com ([156.153.255.213]:48626 "EHLO atlrel7.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754797AbXIZSrl (ORCPT ); Wed, 26 Sep 2007 14:47:41 -0400 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org Herbert Xu wrote: > Stephen Hemminger 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? 0 byte writes are not allowed in SCTP. A no-op is fine, otherwise SCTP would return an error. -vlad > > Put it another way, do we really need to keep the short-circuit > for SOCK_STREAM? > > Cheers,