Bug 453600

Description of problem:
The SNMPD plugin for clustersuite uses the
ClusterMonitoring::ClusterMonitor::get_cluster() method to retrieve the cluster
information.

This in turn calls ClientSocket::recv() -> read_restart().

The read_restart function is designed to fill a buffer with all data currently
buffered on the socket and to return when the underlying read() returns with EAGAIN.

This will only work if the socket has O_NONBLOCK set. Using this method on a
blocking socket will cause the thread calling get_cluster() to block
indefinitely waiting for additional data to arrive on the socket.

Version-Release number of selected component (if applicable):
0.10.0-5.el5 contains the defect but it is masked by bug 441947; rebuilding the
package to avoid the dlopen problem or using a later package (e.g. 0.12.0-7.el5)
allows the bug to be triggered.

How reproducible:
100%

Steps to Reproduce:
1. Configure a cluster with snmpd enabled on the nodes
2. Enable cluster-snmp
3. Try to access a REDHAT-CLUSTER-MIB MIB, e.g. REDHAT-CLUSTER-MIB::rhcMIBVersion.0
  
Actual results:
$ cat /etc/snmp/snmpd.conf
dlmod RedHatCluster     /usr/lib/cluster-snmp/libClusterMonitorSnmp.so
rocommunity public 127.0.0.1
$ snmpwalk -v2c -c public localhost
[tons of output, works fine but doesn't show REDHAT-CLUSTER-MIB::RedHatCluster]
$ snmpwalk -v2c -c public localhost REDHAT-CLUSTER-MIB::RedHatCluster
REDHAT-CLUSTER-MIB::rhcMIBVersion.0 = INTEGER: 1
Timeout: No Response from localhost
$ snmpwalk -v2c -c public localhost
Timeout: No Response from localhost

After this snmpd can only be interrupted by SIGKILL.

Expected results:
MIB output correctly, no hang of snmpd.

Additional info:
Analysis & proposed patch from Adrien Kunysz