Date: Fri, 27 Jan 2006 10:42:04 -0500 From: Kurt Miller <lists@intricatesoftware.com> To: Daniel Eischen <deischen@freebsd.org> Cc: freebsd-hackers@freebsd.org Subject: Re: read hang on datagram socket Message-ID: <200601271042.04315.lists@intricatesoftware.com> In-Reply-To: <Pine.GSO.4.43.0601270909190.10667-100000@sea.ntplx.net> References: <Pine.GSO.4.43.0601270909190.10667-100000@sea.ntplx.net>
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On Friday 27 January 2006 9:16 am, Daniel Eischen wrote:
> On Thu, 26 Jan 2006, Kurt Miller wrote:
>
> > On Thursday 26 January 2006 7:26 pm, Daniel Eischen wrote:
> > >
> > > The modified version does not hang on 5.2. Do you have multiple
> > > interfaces on your 5.4 box?
> >
> > No, the 5.4 box is virtually identical to the 6.0 box. I set them both
> > up at the same time from initial installs for the project.
> >
> > truk@freebsd5-4$ ifconfig
> > lnc0: flags=108843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
> > inet6 fe80::250:56ff:fe40:451a%lnc0 prefixlen 64 scopeid 0x1
> > inet 172.16.1.36 netmask 0xffffff00 broadcast 172.16.1.255
> > ether 00:50:56:40:45:1a
> > lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
> > inet 127.0.0.1 netmask 0xff000000
> > inet6 ::1 prefixlen 128
> > inet6 fe80::1%lo0 prefixlen 64 scopeid 0x2
>
> [ ... ]
>
> > > What happens when you try using non-zero IP addresses and ports?
> > >
> >
> > Setting the ports doesn't effect the problem, however setting the
> > addresses does. It really seems like binding to INADDR_ANY only binds
> > to loopback address 127.0.0.1 and not all the interfaces.
> >
> > If sock1 is bound to the hostAddress and sock2 connects to sock1 at
> > the hostAddress it works ok. If sock1 is bound to INADDR_ANY and sock2
> > connects to sock1 using INADDR_ANY it works. but any mixture of of
> > using INADDR_ANY with the hostAddress fails.
>
> According to Steven's Network Programming, when binding to
> INADDR_ANY, the operating system doesn't assign an address
> until the first write. This is unlike the port, where using
> port 0, an ephemeral port is assigned right away. I don't
> have the book handy right now, so I forgot if the INADDR_ANY
> behavior is only when you have multiple interfaces or not.
The book I'm using is not that clear about it (Advanced
Programming in the UNIX Environment). It does say that using
connect with a datagram socket will receive datagrams only
from the address specified, which seems related to the problem.
> > Unfortunately, I don't have control over the addresses, the java
> > programs do. This particular jck test binds the first socket with
> > INADDR_ANY (InetAddress.getByName("0.0.0.0")) and connects the second
> > socket to the first using the hostAddress (InetAddress.getLocalHost()).
>
> You can try sending a byte before getting the address for the
> port and see if that works. Do you have anything weird, like
> not having a default route (gateway)?
Yes, sending a byte before doing the connect(sock2, &sock1Addres
does work. However, calling connect/send/read after that fails too.
The problem appears to be related to sock1's selection of it source
address, or perhaps the connect call is ignoring the hostAddress and
using the loopback address. The netstat output leads me to believe
it is the latter. It is behaving like a mismatch between source
address of the message and the address enforced by the connect call.
I've confirmed that the sock1Addr struct is filled in correctly with
the hostAddress and port of sock1 and sock2Addr is filled in correctly
with the hostAddress and port of sock2.
I've got a pretty standard setup. All three machines are using DHCP
to get their addresses, default route and name servers. I've set
the dhcp server to give them the same IP addresses each time. Here's
the routing table for each:
truk@freebsd6-0$ netstat -r -f inet
Routing tables
Internet:
Destination Gateway Flags Refs Use Netif Expire
default 172.16.1.1 UGS 0 34 lnc0
localhost localhost UH 0 0 lo0
172.16.1/24 link#1 UC 0 0 lnc0
172.16.1.1 00:00:24:c2:47:b5 UHLW 2 0 lnc0 671
172.16.1.10 00:13:46:c9:0a:5c UHLW 1 0 lnc0 1103
172.16.1.72 00:12:f0:b5:f4:6c UHLW 1 118 lnc0 961
truk@freebsd5-4$ netstat -r -f inet
Routing tables
Internet:
Destination Gateway Flags Refs Use Netif Expire
default 172.16.1.1 UGS 0 112 lnc0
localhost localhost UH 1 19 lo0
172.16.1/24 link#1 UC 0 0 lnc0
172.16.1.1 00:00:24:c2:47:b5 UHLW 1 0 lnc0 40
172.16.1.10 00:13:46:c9:0a:5c UHLW 0 0 lnc0 1106
172.16.1.36 localhost UGHS 0 7 lo0
172.16.1.72 00:12:f0:b5:f4:6c UHLW 0 3151 lnc0 749
$ netstat -r -f inet #freebsd4-11
Routing tables
Internet:
Destination Gateway Flags Refs Use Netif Expire
default 172.16.1.1 UGSc 1 0 lnc0
localhost localhost UH 1 0 lo0
172.16.1/24 link#1 UC 2 0 lnc0
172.16.1.1 00:00:24:c2:47:b5 UHLW 2 0 lnc0 1200
172.16.1.30 localhost UGHS 0 0 lo0
172.16.1.72 00:12:f0:b5:f4:6c UHLW 1 112 lnc0 1195
Thanks for the ideas and suggestions.
-Kurt
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