[Xen-devel] xs_read problem leads segmentation fault

[Gihan Munasinghe <GMunasinghe@xxxxxxxxxxxxxx>]

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


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