[Qemu-devel] [PATCH] Make ping work for -net user

[Qemu-devel] [PATCH] Make ping work for -net user

[jbrown105]

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This is a very simple proof-of-concept patch that fakes ICMP well enough
for ping to work.

Basically, when the slirp code gets a ping request for an ip outside of
the
slirp network, it runs /bin/ping and reports the results back to the
guest
accordingly.

Right now it uses vfork() and then exec() to run ping on the host, as
for
some reason fork() causes qemu to freeze. I'm still trying to figure out
why.

As a consequence I don't close ping's output or error stream so you see
output
from it on the terminal window that qemu is running on.

Tested on a linux host and a linux guest.
-- 
  
  jbrown105@speedymail.org

-- 
http://www.fastmail.fm - Does exactly what it says on the tin


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diff -ur qemu/slirp/ip_icmp.c qemu.new/slirp/ip_icmp.c
--- qemu/slirp/ip_icmp.c	2006-05-03 15:58:17.000000000 -0400
+++ qemu/slirp/ip_icmp.c	2007-08-15 23:23:50.000000000 -0400
@@ -77,7 +77,9 @@
   register struct icmp *icp;
   register struct ip *ip=mtod(m, struct ip *);
   int icmplen=ip->ip_len;
-  /* int code; */
+  int cpid;
+  char * string_dst_ip;
+  int code;
 	
   DEBUG_CALL("icmp_input");
   DEBUG_ARG("m = %lx", (long )m);
@@ -117,48 +119,43 @@
     if (ip->ip_dst.s_addr == alias_addr.s_addr) {
       icmp_reflect(m);
     } else {
-      struct socket *so;
-      struct sockaddr_in addr;
-      if ((so = socreate()) == NULL) goto freeit;
-      if(udp_attach(so) == -1) {
-	DEBUG_MISC((dfd,"icmp_input udp_attach errno = %d-%s\n", 
-		    errno,strerror(errno)));
-	sofree(so);
-	m_free(m);
-	goto end_error;
+      string_dst_ip = inet_ntoa(ip->ip_dst);
+      cpid = vfork();
+      if (cpid == 0)
+      {
+      	execl("/bin/ping", "ping", "-c", "1", string_dst_ip, NULL);
+	_exit(2);
       }
-      so->so_m = m;
-      so->so_faddr = ip->ip_dst;
-      so->so_fport = htons(7);
-      so->so_laddr = ip->ip_src;
-      so->so_lport = htons(9);
-      so->so_iptos = ip->ip_tos;
-      so->so_type = IPPROTO_ICMP;
-      so->so_state = SS_ISFCONNECTED;
-      
-      /* Send the packet */
-      addr.sin_family = AF_INET;
-      if ((so->so_faddr.s_addr & htonl(0xffffff00)) == special_addr.s_addr) {
-	/* It's an alias */
-	switch(ntohl(so->so_faddr.s_addr) & 0xff) {
-	case CTL_DNS:
-	  addr.sin_addr = dns_addr;
-	  break;
-	case CTL_ALIAS:
-	default:
-	  addr.sin_addr = loopback_addr;
-	  break;
-	}
-      } else {
-	addr.sin_addr = so->so_faddr;
+      else if (cpid == -1)
+      {
+	icmp_error(m, ICMP_UNREACH,ICMP_UNREACH_NET, 0,"exec failed"); 
       }
-      addr.sin_port = so->so_fport;
-      if(sendto(so->s, icmp_ping_msg, strlen(icmp_ping_msg), 0,
-		(struct sockaddr *)&addr, sizeof(addr)) == -1) {
-	DEBUG_MISC((dfd,"icmp_input udp sendto tx errno = %d-%s\n",
-		    errno,strerror(errno)));
-	icmp_error(m, ICMP_UNREACH,ICMP_UNREACH_NET, 0,strerror(errno)); 
-	udp_detach(so);
+      else
+      {
+	int x;
+	while ((x = waitpid(cpid, &code, WNOHANG)) != cpid)
+	{
+		if (x != 0)
+		{
+		break;
+		}
+	}
+
+	int i1, i2;
+	i1 = WIFEXITED(code);
+	if (i1)
+	  i2 = WEXITSTATUS(code);
+	else
+	  i2 = 1;
+
+	if (i1 && (i2 == 0))
+	{
+           icmp_reflect(m);
+	}
+	else
+	{
+	   icmp_error(m, ICMP_UNREACH,ICMP_UNREACH_NET, 0,"ping failed"); 
+	}
       }
     } /* if ip->ip_dst.s_addr == alias_addr.s_addr */
     break;
diff -ur qemu/slirp/ip_icmp.h qemu.new/slirp/ip_icmp.h
--- qemu/slirp/ip_icmp.h	2005-06-05 13:11:42.000000000 -0400
+++ qemu.new/slirp/ip_icmp.h	2007-08-15 21:42:17.000000000 -0400
@@ -161,4 +161,7 @@
 void icmp_error _P((struct mbuf *, u_char, u_char, int, char *));
 void icmp_reflect _P((struct mbuf *));
 
+#include <sys/wait.h>
+#include <unistd.h>
+
 #endif

Re: [Qemu-devel] [PATCH] Make ping work for -net user

[Luke -Jr]

On Thursday 16 August 2007, jbrown105@speedymail.org wrote:
> This is a very simple proof-of-concept patch that fakes ICMP well enough
> for ping to work.

Speaking of which... does ping work if qemu runs as root?
As to the patch, it looks like it only works if you're testing whether you 
actually can ping or not. It wouldn't work with, for example, icmptx.