RE: Can we make pipefds[0] in netsnmp_callback_transport() asnon-blocking fds.?

All,
 
We found the problem of read() on fd getting blocked when select()
returns with a read-fd set. We were calling snmp_read() twice in our
code flow and hence read() was getting blocked. This problem is now
solved without any change in the net-snmp code.
 
Regards,
Suresh.
 
 

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
Pamidipati Suresh-G20238
Sent: Tuesday, October 03, 2006 11:49 PM
To: [email protected]
Subject: Can we make pipefds[0] in netsnmp_callback_transport()
asnon-blocking fds.?


Hi All,
 
We are using Net-snmp-5.2.2 as Agentx subagent and master agent.
 
In Subagent, we are observing that "select()" returns with a read-fd
set, but a subsequent "read()" call on that fd is getting blocked. The
fd-pair being used here, is created using the "pipe()" call. 
 
We observed that read() call is blocked at line no 194 in
netsnmp_callback_recv() function of snmpCallbackDomain.c file. Following
is the code snippet.
 
    188     DEBUGMSGTL(("transport_callback", "hook_recv enter\n"));
    189
    190     while (rc < 0) {
    191 #ifdef WIN32
    192         rc = recv(mystuff->pipefds[0], newbuf, 1, 0);
    193 #else
    194         rc = read(mystuff->pipefds[0], newbuf, 1);
    195 #endif
    196         if (rc < 0 && errno != EINTR) {
    197             break;
    198         }
    199     }
    200

We have seen this problem in Montavista linux CGE - 4.0. 
 
After going through the Net-snmp code, we found that pipefds created
using pipe() call are not set as non-blocking fds. 
Please let us know if we change the pipefds[0] as non-blocking fds as
follows, will there be any impact in the functionality of Subagent and
Master agent.
 
netsnmp_transport *
netsnmp_callback_transport(int to)
{
int enable_nbio;
. . . 
. . .
    rc = pipe(mydata->pipefds);
    ioctl(mydata->pipefds[0], FIONBIO, &enable_nbio);
.  . . 
. . . 
}
 
Any information on this will be really helpful. 
 
Thanks,
Suresh.

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