xs_read problem leads segmentation fault

xs_read problem leads segmentation fault

[Gihan Munasinghe]

Hi

I am having a problem with xs_read..
In my program I want to create a VM and get the vnc port out of it.. and 
this is a multi threaded programs.. but I have made sure that there will 
be only one create at a time

This is the function that reads the vnc port off the xenstore
------------------------------------------------------------------------------------------------------------------------------
/**
 * Returns the VNC port for a given dom ID
 * 0 in case of a failure
 */
unsigned int get_vnc_port(unsigned int dom_id){
            unsigned int port = 0;
                unsigned int len=0;
        struct xs_handle* xsn;
        xsn = connect_to_xenstore();
        if(xsn){
                char s[40];
                snprintf(s, 39, "/local/domain/%u/console/vnc-port", 
dom_id);
                s[39] = 0;
                LOG_INFO_MSG("Trying to read %s off XEN Store",s);
                char *vnc_port = (char *)xs_read(xs,0,&s[0],&len);
                LOG_INFO_MSG("Value read %p off XEN Store LEN 
%u",vnc_port,len);
                close_conn_xenstore(xsn);
                if(vnc_port && len>0){
                        LOG_INFO_MSG("VNC port from xs %s ",vnc_port);
                        port = atoi(vnc_port);
                        free(vnc_port);
                        LOG_INFO_MSG("VNC port for dom %u is %u 
",dom_id,port);
                }else{
                        LOG_ERROR_MSG("Could Not get the VNC port for 
dom %u",dom_id);
                }

        }else{
                LOG_ERROR_MSG("Could Not Connect to xenstore");
        }
        return port;
}
---------------------------------------------------------------------------------------------

This code works most of the time but at some point it gives segmentation 
fault
The Logging Info
  LOG_INFO_MSG("Value read %p off XEN Store LEN %u",vnc_port,len);
log out the following before the segmentation fault happens (seems like 
some sort of a garbage memory )
Mar  5 14:16:50 Agent: [25238]: Value read 0xffffffffac0008f0 off XEN 
Store LEN 4

When this work The info log looks as follows
Mar  5 14:16:43 Agent: [25238]: Value read 0x63e5a0 off XEN Store LEN 4

Does any one have ant insight to why this is happening.. or a way of 
avoiding this..

Thanks

-- 
Gihan Munasinghe
Development Team Leader
XCalibre Communications Ltd.
www.flexiscale.com