lguest: clean up warnings in demonstration launcher.

These days the headers we use are in glibc.  If those are too old, you can
add the -I lines to get the kernel headers.

In file included from ../../include/linux/if_tun.h:19,
                 from lguest.c:33:
../../include/linux/types.h:13:2: warning: #warning "Attempt to use kernel headers from user space, see http://kernelnewbies.org/KernelHeaders"
lguest.c: In function ‘setup_tun_net’:
lguest.c:1456: warning: dereferencing pointer ‘sin’ does break strict-aliasing rules
lguest.c:1457: warning: dereferencing pointer ‘sin’ does break strict-aliasing rules
lguest.c:1450: note: initialized from here
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Documentation/lguest/Makefile

 # This creates the demonstration utility "lguest" which runs a Linux guest.
-CFLAGS:=-m32 -Wall -Wmissing-declarations -Wmissing-prototypes -O3 -I../../include -I../../arch/x86/include -U_FORTIFY_SOURCE
+# Missing headers?  Add "-I../../include -I../../arch/x86/include"
+CFLAGS:=-m32 -Wall -Wmissing-declarations -Wmissing-prototypes -O3 -U_FORTIFY_SOURCE
 
 all: lguest
 

Documentation/lguest/lguest.c

@@ -39,14 +39,14 @@
 #include <limits.h>
 #include <stddef.h>
 #include <signal.h>
-#include "linux/lguest_launcher.h"
-#include "linux/virtio_config.h"
-#include "linux/virtio_net.h"
-#include "linux/virtio_blk.h"
-#include "linux/virtio_console.h"
-#include "linux/virtio_rng.h"
-#include "linux/virtio_ring.h"
-#include "asm/bootparam.h"
+#include <linux/virtio_config.h>
+#include <linux/virtio_net.h>
+#include <linux/virtio_blk.h>
+#include <linux/virtio_console.h>
+#include <linux/virtio_rng.h>
+#include <linux/virtio_ring.h>
+#include <asm/bootparam.h>
+#include "../../include/linux/lguest_launcher.h"
 /*L:110
  * We can ignore the 42 include files we need for this program, but I do want
  * to draw attention to the use of kernel-style types.
@@ -1447,14 +1447,15 @@ static void add_to_bridge(int fd, const char *if_name, const char *br_name)
 static void configure_device(int fd, const char *tapif, u32 ipaddr)
 {
 	struct ifreq ifr;
-	struct sockaddr_in *sin = (struct sockaddr_in *)&ifr.ifr_addr;
+	struct sockaddr_in sin;
 
 	memset(&ifr, 0, sizeof(ifr));
 	strcpy(ifr.ifr_name, tapif);
 
 	/* Don't read these incantations.  Just cut & paste them like I did! */
-	sin->sin_family = AF_INET;
-	sin->sin_addr.s_addr = htonl(ipaddr);
+	sin.sin_family = AF_INET;
+	sin.sin_addr.s_addr = htonl(ipaddr);
+	memcpy(&ifr.ifr_addr, &sin, sizeof(sin));
 	if (ioctl(fd, SIOCSIFADDR, &ifr) != 0)
 		err(1, "Setting %s interface address", tapif);
 	ifr.ifr_flags = IFF_UP;