Change from using poll(2) to kqueue/kevent when waiting for a DNS

response to return.  This will stop processes waiting on DNS requests
from being woken up when a select collision occurs.  This was tested
on mx1.FreeBSD.org (outgoing mail for the FreeBSD.org mailing
lists.)

Reviewed by:	jlemon, peter

1 files changed, 30 insertions, 32 deletions

diff --git a/lib/libc/net/res_send.c b/lib/libc/net/res_send.c
index 5eb42cf..e720fc7 100644
--- a/lib/libc/net/res_send.c
+++ b/lib/libc/net/res_send.c
@@ -79,6 +79,7 @@ static char rcsid[] = "$FreeBSD$";
  */
 
 #include <sys/types.h>
+#include <sys/event.h>
 #include <sys/param.h>
 #include <sys/time.h>
 #include <sys/socket.h>
@@ -95,7 +96,6 @@ static char rcsid[] = "$FreeBSD$";
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
-#include <poll.h>
 
 #include "res_config.h"
 
@@ -356,6 +356,7 @@ res_send(buf, buflen, ans, anssiz)
 	HEADER *hp = (HEADER *) buf;
 	HEADER *anhp = (HEADER *) ans;
 	int gotsomewhere, connreset, terrno, try, v_circuit, resplen, ns, n;
+	int kq;
 	u_int badns;	/* XXX NSMAX can't exceed #/bits in this variable */
 
 	if ((_res.options & RES_INIT) == 0 && res_init() == -1) {
@@ -374,6 +375,11 @@ res_send(buf, buflen, ans, anssiz)
 	terrno = ETIMEDOUT;
 	badns = 0;
 
+	if ((kq = kqueue()) < 0) {
+		Perror(stderr, "kqueue", errno);
+		return (-1);
+	}
+
 	/*
 	 * Send request, RETRY times, or until successful
 	 */
@@ -414,6 +420,7 @@ res_send(buf, buflen, ans, anssiz)
 					res_close();
 					goto next_ns;
 				case res_done:
+					close(kq);
 					return (resplen);
 				case res_modified:
 					/* give the hook another try */
@@ -423,6 +430,7 @@ res_send(buf, buflen, ans, anssiz)
 				case res_error:
 					/*FALLTHROUGH*/
 				default:
+					close(kq);
 					return (-1);
 				}
 			} while (!done);
@@ -587,9 +595,8 @@ read_len:
 			/*
 			 * Use datagrams.
 			 */
-			struct pollfd pfd;
-			int msec;
-			struct timeval timeout, itv;
+			struct kevent kv;
+			struct timespec timeout;
 			struct sockaddr_storage from;
 			int fromlen;
 
@@ -693,42 +700,30 @@ read_len:
 			 * Wait for reply
 			 */
 
-			msec = (_res.retrans << try) * 1000;
+			timeout.tv_sec = (_res.retrans << try);
 			if (try > 0)
-				msec /= _res.nscount;
-			if (msec <= 0)
-				msec = 1000;
-			gettimeofday(&timeout, NULL);
-			itv.tv_sec = msec / 1000;
-			itv.tv_usec = (msec % 1000) * 1000;
-			timeradd(&timeout, &itv, &timeout);
-
+				timeout.tv_sec /= _res.nscount;
+			if ((long) timeout.tv_sec <= 0)
+				timeout.tv_sec = 1;
+			timeout.tv_nsec = 0;
     wait:
 			if (s < 0) {
 				Perror(stderr, "s out-of-bounds", EMFILE);
 				res_close();
 				goto next_ns;
 			}
-			pfd.fd = s;
-			pfd.events = POLLIN;
-			n = poll(&pfd, 1, msec);
+			
+			kv.ident = s;
+			kv.flags = EV_ADD | EV_ONESHOT;
+			kv.filter = EVFILT_READ;
+				
+			n = kevent(kq, &kv, 1, &kv, 1, &timeout);
 			if (n < 0) {
-				if (errno == EINTR) {
-					struct timeval ctv;
-
-					gettimeofday(&ctv, NULL);
-					if (timercmp(&ctv, &timeout, <)) {
-						timersub(&timeout,
-						    &ctv, &ctv);
-						msec = ctv.tv_sec * 1000;
-						msec += ctv.tv_usec / 1000;
-						goto wait;
-					}
-				} else {
-					Perror(stderr, "poll", errno);
-					res_close();
-					goto next_ns;
-				}
+				if (errno == EINTR)
+					goto wait;
+				Perror(stderr, "kevent", errno);
+				res_close();
+				goto next_ns;
 			}
 
 			if (n == 0) {
@@ -873,16 +868,19 @@ read_len:
 				case res_error:
 					/*FALLTHROUGH*/
 				default:
+					close(kq);
 					return (-1);
 				}
 			} while (!done);
 
 		}
+		close(kq);
 		return (resplen);
     next_ns: ;
 	   } /*foreach ns*/
 	} /*foreach retry*/
 	res_close();
+	close(kq);
 	if (!v_circuit) {
 		if (!gotsomewhere)
 			errno = ECONNREFUSED;	/* no nameservers found */