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
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)
{
netsnmp_callback_transport(int to)
{
int enable_nbio;
. . .
. . .
rc =
pipe(mydata->pipefds);
ioctl(mydata->pipefds[0], FIONBIO, &enable_nbio);
. . .
ioctl(mydata->pipefds[0], FIONBIO, &enable_nbio);
. . .
. . .
}
Any information on this will be really helpful.
Thanks,
Suresh.
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