From 85237d203bc9dfe549218c72686a611cff6368b4 Mon Sep 17 00:00:00 2001
From: maxim <maxim@FreeBSD.org>
Date: Mon, 24 Jan 2005 13:27:24 +0000
Subject: [PATCH] o Try hard to guess a buffer size for a fast growing routing
 table. An approach taken from killall/killall.c.

PR:		bin/76075
Submitted by:	Dmitrij Tejblum
MFC after:	3 weeks
---
 usr.sbin/arp/arp.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/usr.sbin/arp/arp.c b/usr.sbin/arp/arp.c
index 9c794aeae493..32c0bc258501 100644
--- a/usr.sbin/arp/arp.c
+++ b/usr.sbin/arp/arp.c
@@ -456,12 +456,12 @@ search(u_long addr, action_fn *action)
 {
 	int mib[6];
 	size_t needed;
-	char *lim, *buf, *next;
+	char *lim, *buf, *newbuf, *next;
 	struct rt_msghdr *rtm;
 	struct sockaddr_inarp *sin2;
 	struct sockaddr_dl *sdl;
 	char ifname[IF_NAMESIZE];
-	int found_entry = 0;
+	int st, found_entry = 0;
 
 	mib[0] = CTL_NET;
 	mib[1] = PF_ROUTE;
@@ -473,9 +473,19 @@ search(u_long addr, action_fn *action)
 		err(1, "route-sysctl-estimate");
 	if (needed == 0)	/* empty table */
 		return 0;
-	if ((buf = malloc(needed)) == NULL)
-		err(1, "malloc");
-	if (sysctl(mib, 6, buf, &needed, NULL, 0) < 0)
+	buf = NULL;
+	do {
+		needed += needed / 2;
+		newbuf = realloc(buf, needed);
+		if (newbuf == NULL) {
+			if (buf != NULL)
+				free(buf);
+			errx(1, "could not reallocate memory");
+		}
+		buf = newbuf;
+		st = sysctl(mib, 6, buf, &needed, NULL, 0);
+	} while (st == -1 && errno == ENOMEM);
+	if (st == -1)
 		err(1, "actual retrieval of routing table");
 	lim = buf + needed;
 	for (next = buf; next < lim; next += rtm->rtm_msglen) {