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 09:54:28.000000000 -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; > > + } > > > > 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
