/*  * This file is part of the UCB release of Plan 9. It is subject to the license * terms in the LICENSE file found in the top-level directory of this * distribution and at http://akaros.cs.berkeley.edu/files/Plan9License. No * part of the UCB release of Plan 9, including this file, may be copied, * modified, propagated, or distributed except according to the terms contained * in the LICENSE file. */ #include <u.h>#include <libc.h>#include <ip.h>#include "../icmp.h" static voidcatch(void *a, char *msg){	USED(a);	if(strstr(msg, "alarm"))		noted(NCONT);	else		noted(NDFLT);} #define MSG "dhcp probe" /* *  make sure noone is using the address *  TODO: ipv6 ping */inticmpecho(uchar *a){	int fd, i, n, len, rv;	ushort sseq, x;	char buf[512];	Icmphdr *ip; 	rv = 0;	if (!isv4(a))		return 0;	sprint(buf, "%I", a);	fd = dial(netmkaddr(buf, "icmp", "1"), 0, 0, 0);	if(fd < 0){		return 0;	} 	sseq = getpid()*time(0); 	ip = (Icmphdr *)(buf + IPV4HDR_LEN);	notify(catch);	for(i = 0; i < 3; i++){		ip->type = EchoRequest;		ip->code = 0;		strcpy((char*)ip->data, MSG);		ip->seq[0] = sseq;		ip->seq[1] = sseq>>8;		len = IPV4HDR_LEN + ICMP_HDRSIZE + sizeof(MSG); 		/* send a request */		if(write(fd, buf, len) < len)			break; 		/* wait 1/10th second for a reply and try again */		alarm(100);		n = read(fd, buf, sizeof(buf));		alarm(0);		if(n <= 0)			continue; 		/* an answer to our echo request? */		x = (ip->seq[1]<<8) | ip->seq[0];		if(n >= len && ip->type == EchoReply && x == sseq &&		    strcmp((char*)ip->data, MSG) == 0){			rv = 1;			break;		}	}	close(fd);	return rv;}