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 09:54:28.000000000 -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.
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
