From ec4b56789488a76d0dd57bb7e08846e23aba2b3e Mon Sep 17 00:00:00 2001
From: Erik van der Kouwe <erik@minix3.org>
Date: Thu, 3 Sep 2009 20:35:22 +0000
Subject: [PATCH] Avoid alarm to prevent the setitimer interval from being
 reset

---
 lib/ip/res_send.c | 59 ++++++++++++++++++++++-------------------------
 1 file changed, 28 insertions(+), 31 deletions(-)

diff --git a/lib/ip/res_send.c b/lib/ip/res_send.c
index 1c6dbe4c1..88090f3f1 100755
--- a/lib/ip/res_send.c
+++ b/lib/ip/res_send.c
@@ -56,6 +56,7 @@ static char sccsid[] = "@(#)res_send.c	6.27 (Berkeley) 2/24/91";
 
 #include <sys/types.h>
 #include <sys/ioctl.h>
+#include <sys/select.h>
 #include <sys/stat.h>
 #include <assert.h>
 #include <errno.h>
@@ -87,7 +88,6 @@ static int udp_sendto _ARGS(( int fd, const char *buf, unsigned buflen,
 				ipaddr_t addr, Udpport_t port ));
 static int udp_receive _ARGS(( int fd, char *buf, unsigned buflen,
 				time_t timeout ));
-static void alarm_handler _ARGS(( int sig ));
 
 #endif /* !_MINIX */
 
@@ -843,13 +843,6 @@ udpport_t port;
 	return r;
 }
 
-static void alarm_handler(sig)
-int sig;
-{
-	signal(SIGALRM, alarm_handler);
-	alarm(1);
-}
-
 static int udp_receive(fd, buf, buflen, timeout)
 int fd;
 char *buf;
@@ -859,45 +852,49 @@ time_t timeout;
 	char *newbuf;
 	udp_io_hdr_t *udp_io_hdr;
 	int r, terrno;
-	void (*u_handler) _ARGS(( int sig ));
-	time_t u_timeout;
-
-	newbuf= malloc(sizeof(*udp_io_hdr) + buflen);
+	fd_set readfds;
+	struct timeval timeval;
+	
+	/* allocate buffer for packet */
+	newbuf = malloc(sizeof(*udp_io_hdr) + buflen);
 	if (newbuf == NULL)
 	{
-		errno= ENOMEM;
+		errno = ENOMEM;
 		return -1;
 	}
+	
+	/* only read if there is something to be read within timeout seconds */
+	FD_ZERO(&readfds);
+	FD_SET(fd, &readfds);
+	timeval.tv_sec = timeout;
+	timeval.tv_usec = 0;
+	r = select(fd + 1, &readfds, NULL, NULL, &timeval);
+	if (r >= 0 && !FD_ISSET(fd, &readfds))
+	{
+		errno = EINTR;
+		r = -1;
+	}
 
-	u_handler= signal(SIGALRM, alarm_handler);
-	u_timeout= alarm(timeout);
-
-	r= read(fd, newbuf, sizeof(*udp_io_hdr) + buflen);
-	terrno= errno;
+	if (r >= 0)
+		r = read(fd, newbuf, sizeof(*udp_io_hdr) + buflen);
 
+	/* clean up in case of failure */
+	terrno = errno;
 	if (r < 0 || r <= sizeof(*udp_io_hdr))
 	{
 		if (r > 0)
-			r= 0;
-		free(newbuf);
-
-
-		alarm(0);
-		signal(SIGALRM, u_handler);
-		alarm(u_timeout);
+			r = 0;
 
-		errno= terrno;
+		free(newbuf);
+		errno = terrno;
 		return r;
 	}
 
+	/* copy packet body to caller-provided buffer */
 	memcpy(buf, newbuf + sizeof(*udp_io_hdr), r - sizeof(*udp_io_hdr));
 	free(newbuf);
 
-	alarm(0);
-	signal(SIGALRM, u_handler);
-	alarm(u_timeout);
-
-	return r-sizeof(*udp_io_hdr);
+	return r - sizeof(*udp_io_hdr);
 }
 
 #endif
-- 
2.44.0