snmp: use poll() to wait for AgentX socket to be ready

Instead of sleeping for an arbitrary amount of time, query if the socket
is ready using poll() which should be portable enough (POSIX.1-2001) to
work everywhere.

diff --git a/src/daemon/agent_priv.c b/src/daemon/agent_priv.c
index 88e8e95813c58392671a7c60d88e125b7ba4c1df..8efcb5e37cc4947fea6ce42ed73891827c215aee 100644 (file)
--- a/src/daemon/agent_priv.c
+++ b/src/daemon/agent_priv.c
@@ -24,6 +24,7 @@
 
 #include <unistd.h>
 #include <errno.h>
+#include <poll.h>
 
 #ifdef ENABLE_PRIVSEP
 #include <net-snmp/net-snmp-config.h>
@@ -59,6 +60,7 @@ agent_priv_unix_recv(netsnmp_transport *t, void *buf, int size,
                goto recv_error;
        while (rc < 0) {
                rc = recv(t->sock, buf, size, 0);
+               /* TODO: handle the (unlikely) case where we get EAGAIN or EWOULDBLOCK */
                if (rc < 0 && errno != EINTR) {
                        log_warn("snmp", "unable to receive from fd %d",
                            t->sock);
@@ -76,31 +78,46 @@ recv_error:
        return -1;
 }
 
+#define AGENT_WRITE_TIMEOUT 2000
 static int
 agent_priv_unix_send(netsnmp_transport *t, void *buf, int size,
     void **opaque, int *olength)
 {
-       int rc = -1, retry = 4;
-       useconds_t usecs = 250000;
+       int rc = -1;
+       struct pollfd sagentx = {
+               .fd = t->sock,
+               .events = POLLOUT | POLLERR | POLLHUP
+       };
 
        if (t != NULL && t->sock >= 0) {
                while (rc < 0) {
-                       rc = send(t->sock, buf, size, 0);
-                       if (rc < 0) {
-                               if (errno == EAGAIN || errno == EWOULDBLOCK) {
-                                       if (--retry <= 0)
-                                               break;
-
-                                       log_info("snmp", "%s: retrying after "
-                                               "%d secs...\n", __FUNCTION__,
-                                               usecs);
-                                       usleep(usecs);
-                                       continue;
-                               } else if (errno != EINTR) {
-                                       log_info("snmp", "%s: failed with %s\n",
-                                               __FUNCTION__, strerror(errno));
+                       rc = poll(&sagentx, 1, AGENT_WRITE_TIMEOUT);
+                       if (rc == 0) {
+                               log_warnx("snmp",
+                                   "timeout while communicating with the master agent");
+                               rc = -1;
+                               break;
+                       }
+                       if (rc > 0) {
+                               /* We can either write or have an error somewhere */
+                               rc = send(t->sock, buf, size, 0);
+                               if (rc < 0) {
+                                       if (errno == EAGAIN ||
+                                           errno == EWOULDBLOCK ||
+                                           errno == EINTR)
+                                               /* Let's retry */
+                                               continue;
+                                       log_warn("snmp",
+                                           "error while sending to master agent");
+                                       break;
+                               }
+                       } else {
+                               if (errno != EINTR) {
+                                       log_warn("snmp",
+                                           "error while attempting to send to master agent");
                                        break;
                                }
+                               continue;
                        }
                }
        }