[RFC] Zero-length write() does not generate a datagram on connected socket
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 09:54:28.0 -0700 +++ b/net/socket.c 2007-09-24 15:31:25.0 -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; + } x = alloc_sock_iocb(iocb, &siocb); if (!x) - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [RFC] Zero-length write() does not generate a datagram on connected socket
Stephen Hemminger <[EMAIL PROTECTED]> 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 09:54:28.0 -0700 > +++ b/net/socket.c 2007-09-24 15:31:25.0 -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~} <[EMAIL PROTECTED]> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [RFC] Zero-length write() does not generate a datagram on connected socket
On Wed, 26 Sep 2007 11:18:39 +0800 Herbert Xu <[EMAIL PROTECTED]> wrote: > Stephen Hemminger <[EMAIL PROTECTED]> 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 09:54:28.0 -0700 > > +++ b/net/socket.c 2007-09-24 15:31:25.0 -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, Stream is defined as sequence of bytes. So short circuit makes sense If the application wants message boundaries it needs to use SOCK_SEQPACKET. I was paranoid about possible breakage in TCP or SCTP. But since send(s, buf, 0, 0) already filters through, I guess it doesn't matter. -- Stephen Hemminger <[EMAIL PROTECTED]> - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [RFC] Zero-length write() does not generate a datagram on connected socket
Herbert Xu wrote: Stephen Hemminger <[EMAIL PROTECTED]> 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 09:54:28.0 -0700 +++ b/net/socket.c 2007-09-24 15:31:25.0 -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? I asked Vlad that very question, since SCTP can preserve message boundaries. He tells me that a zero-length message is not part of SCTP. rick jones - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [RFC] Zero-length write() does not generate a datagram on connected socket
Herbert Xu wrote: > Stephen Hemminger <[EMAIL PROTECTED]> 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 09:54:28.0 -0700 >> +++ b/net/socket.c 2007-09-24 15:31:25.0 -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, - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [RFC] Zero-length write() does not generate a datagram on connected socket
From: Stephen Hemminger <[EMAIL PROTECTED]> Date: Mon, 24 Sep 2007 15:34:35 -0700 > 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.c2007-08-20 09:54:28.0 -0700 > +++ b/net/socket.c2007-09-24 15:31:25.0 -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; > + } > > x = alloc_sock_iocb(iocb, &siocb); > if (!x) We should simply remove the check completely. There is no need to add special code for different types of protocols and sockets. As is hinted in the bugzilla, the exact same thing can happen with a suitably constructed sendto() or sendmsg() call. write() on a socket is a sendmsg() with a NULL msg_control and a single entry iovec, plain and simple. It's how BSD and many other systems behave, and I double checked Steven's Volume 2 just to make sure. So I'm going to check in the following to fix this bugzilla. There is a similarly ugly test for len==0 in sys_read() on sockets. If someone would do some research on the validity of that thing I'd really appreciate it :-) diff --git a/net/socket.c b/net/socket.c index 7d44453..b09eb90 100644 --- a/net/socket.c +++ b/net/socket.c @@ -777,9 +777,6 @@ static ssize_t sock_aio_write(struct kiocb *iocb, const struct iovec *iov, if (pos != 0) return -ESPIPE; - if (iocb->ki_left == 0) /* Match SYS5 behaviour */ - return 0; - x = alloc_sock_iocb(iocb, &siocb); if (!x) return -ENOMEM; - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [RFC] Zero-length write() does not generate a datagram on connected socket
On Thu, 27 Sep 2007 13:53:34 -0700 (PDT) David Miller <[EMAIL PROTECTED]> wrote: > From: Stephen Hemminger <[EMAIL PROTECTED]> > Date: Mon, 24 Sep 2007 15:34:35 -0700 > > > 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 09:54:28.0 -0700 > > +++ b/net/socket.c 2007-09-24 15:31:25.0 -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; > > + } > > > > x = alloc_sock_iocb(iocb, &siocb); > > if (!x) > > We should simply remove the check completely. > > There is no need to add special code for different types of protocols > and sockets. > > As is hinted in the bugzilla, the exact same thing can happen with a > suitably constructed sendto() or sendmsg() call. write() on a socket > is a sendmsg() with a NULL msg_control and a single entry iovec, plain > and simple. > > It's how BSD and many other systems behave, and I double checked > Steven's Volume 2 just to make sure. > > So I'm going to check in the following to fix this bugzilla. There is > a similarly ugly test for len==0 in sys_read() on sockets. If someone > would do some research on the validity of that thing I'd really > appreciate it :-) Read of zero length should be a no-op for SOCK_STREAM but for SOCK_DATAGRAM or SOCK_SEQPACKET it might be useful as a remote wait for event. -- Stephen Hemminger <[EMAIL PROTECTED]> - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [RFC] Zero-length write() does not generate a datagram on connected socket
On 9/28/07, Stephen Hemminger <[EMAIL PROTECTED]> wrote: > On Thu, 27 Sep 2007 13:53:34 -0700 (PDT) > David Miller <[EMAIL PROTECTED]> wrote: > > > From: Stephen Hemminger <[EMAIL PROTECTED]> > > Date: Mon, 24 Sep 2007 15:34:35 -0700 > > > > > 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 09:54:28.0 -0700 > > > +++ b/net/socket.c 2007-09-24 15:31:25.0 -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; > > > + } > > > > > > x = alloc_sock_iocb(iocb, &siocb); > > > if (!x) > > > > We should simply remove the check completely. > > > > There is no need to add special code for different types of protocols > > and sockets. > > > > As is hinted in the bugzilla, the exact same thing can happen with a > > suitably constructed sendto() or sendmsg() call. write() on a socket > > is a sendmsg() with a NULL msg_control and a single entry iovec, plain > > and simple. > > > > It's how BSD and many other systems behave, and I double checked > > Steven's Volume 2 just to make sure. > > > > So I'm going to check in the following to fix this bugzilla. There is > > a similarly ugly test for len==0 in sys_read() on sockets. If someone > > would do some research on the validity of that thing I'd really > > appreciate it :-) > > Read of zero length should be a no-op for SOCK_STREAM but > for SOCK_DATAGRAM or SOCK_SEQPACKET it might be useful as a > remote wait for event. Hmm -- I hadn't checked the behavior for zero-length read() on other systems. i will try to do that soonish (probably only Minday or so). Cheers, Michael - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html