Description of problem: fence_xvmd cannot start if default route is set.


Version-Release number of selected component (if applicable):
cman-2.0.84-2.el5


How reproducible: always


Steps to Reproduce:
1. del or not set default route
2. start fence_xvmd by manual (with -f option not to be daemon)

Here is the log:

[root@cluster-1 ~]# rpm -qf /sbin/fence_xvmd
cman-2.0.84-2.el5
[root@cluster-1 ~]# fence_xvmd -LX -fddd
Debugging threshold is now 3
-- args @ 0xbfd70fbc --
  args->addr = 225.0.0.12
  args->domain = (null)
  args->key_file = /etc/cluster/fence_xvm.key
  args->op = 2
  args->hash = 2
  args->auth = 2
  args->port = 1229
  args->family = 2
  args->timeout = 30
  args->retr_time = 20
  args->flags = 259
  args->debug = 3
-- end args --
Reading in key file /etc/cluster/fence_xvm.key into 0xbfd6ffbc (4096 max size)
Actual key length = 4096 bytesMy Node ID = 1
Domain                   UUID                                 Owner State
------                   ----                                 ----- -----
Domain-0                 00000000-0000-0000-0000-000000000000 00001 00001
[root@cluster-1 ~]# ip route show
192.168.12.0/24 dev virbr0  proto kernel  scope link  src 192.168.12.1
192.168.122.0/24 dev eth0  proto kernel  scope link  src 192.168.122.11
169.254.0.0/16 dev eth0  scope link
default via 192.168.122.1 dev eth0
[root@cluster-1 ~]# ip route del default via 192.168.122.1 dev eth0
[root@cluster-1 ~]# ip route show
192.168.12.0/24 dev virbr0  proto kernel  scope link  src 192.168.12.1
192.168.122.0/24 dev eth0  proto kernel  scope link  src 192.168.122.11
169.254.0.0/16 dev eth0  scope link
[root@cluster-1 ~]# fence_xvmd -LX -fddd
Debugging threshold is now 3
-- args @ 0xbf93662c --
  args->addr = 225.0.0.12
  args->domain = (null)
  args->key_file = /etc/cluster/fence_xvm.key
  args->op = 2
  args->hash = 2
  args->auth = 2
  args->port = 1229
  args->family = 2
  args->timeout = 30
  args->retr_time = 20
  args->flags = 259
  args->debug = 3
-- end args --
Reading in key file /etc/cluster/fence_xvm.key into 0xbf93562c (4096 max size)
Actual key length = 4096 bytesFailed to bind multicast receive socket to 225.0.0.12: No such device
Check network configuration.
Could not set up multicast listen socket
[root@cluster-1 ~]# ip route add default via 192.168.122.1 dev eth0
[root@cluster-1 ~]# fence_xvmd -LX -fddd
Debugging threshold is now 3
-- args @ 0xbfb76dbc --
  args->addr = 225.0.0.12
  args->domain = (null)
  args->key_file = /etc/cluster/fence_xvm.key
  args->op = 2
  args->hash = 2
  args->auth = 2
  args->port = 1229
  args->family = 2
  args->timeout = 30
  args->retr_time = 20
  args->flags = 259
  args->debug = 3
-- end args --
Reading in key file /etc/cluster/fence_xvm.key into 0xbfb75dbc (4096 max size)
Actual key length = 4096 bytesMy Node ID = 1
Domain                   UUID                                 Owner State
------                   ----                                 ----- -----
Domain-0                 00000000-0000-0000-0000-000000000000 00001 00001
[root@cluster-1 ~]#



Actual results: it cannot start


Expected results: it starts w/o any problems.


Additional info:
This probelm is because that interface to listen is not selected explicitly in 
both ipv4 and ipv6 code, I think.

It's my understanding that listening interface is selected by linux kernel in
this case and it should be the one to default gw if appropriate route to 
the multicast network to join is not set. (do_ip_setsockopt, ip_mc_join_group
and other related functions in kernel/net/ipv4/ip_sockglue.c).

Also, this behavior checks with the BSD variants' behavior noted in the 
multicast section in the very famous book, Unix networking programming.


There is another problem behind this. 

There is no way to indicate fence_xvmd to select correct interface if host has 
multiple network interfaces. So, fence_xvmd might listen on wrong interface and 
cannot communicate with fence_xvm at all.


To fix these problems, fence_xvmd must have the way to select correct interface
to listen.

I'll post a patch solves these problems at once.