[Qemu-devel] [PATCH] Add -tun option for preconfigured interface

[Jean-Christian de Rivaz <jc@eclis.ch>]

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I like that the root on the host OS can assign TUN interface to users 
and that the root configure it. So the user only use the new -tun 
<devname> option to use the preconfigured TUN interface without the need 
to execute a trick and unsecure script.

Here is the added desciption:
----------------------------------------------------------------------
-tun devname	
     Try to use devname while opening a tap/tun host network interface 
and use it. If it work, the network init script is not executed for this 
interface. If it don't work, the interface will use the name assigned by 
the operating system and the network init script is executed.

      This option permit the use of preconfigured interface. For 
example, as root you can assign a tun interface to a user and configure 
it like this:

            tunctl -u bob -t tun2
            ifconfig tun2 192.168.2.1

      Then bob can use this interface with the option "-tun tun2". Note 
that option permit the use of a DHCP server on the host to configure the 
guest interface.
----------------------------------------------------------------------

I have also patched the qemu-doc.html but cvs diff don't work with it.

I have tryed to be compatible with the -tun-fd option, but this is 
untested. Also the tun_open() function for BSD system will probably not 
handle this case as expected.
-- 
Jean-Christian de Rivaz

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Index: qemu-doc.texi
===================================================================
RCS file: /cvsroot/qemu/qemu/qemu-doc.texi,v
retrieving revision 1.55
diff -u -r1.55 qemu-doc.texi
--- qemu-doc.texi	10 Feb 2005 21:46:47 -0000	1.55
+++ qemu-doc.texi	13 Feb 2005 01:59:04 -0000
@@ -212,6 +212,22 @@
 aa:bb:cc:dd:ee:ff in hexa). The mac address is incremented for each
 new network interface.
 
+@item -tun devname
+Try to use @var{devname} while opening a tap/tun host network interface and use
+it. If it work, the network init script is not executed for this
+interface. If it don't work, the interface will use the name assigned
+by the operating system and the network init script is executed.
+
+This option permit the use of preconfigured interface. For example, as
+root you can assign a tun interface to a user and configure it like this:
+@example
+tunctl -u bob -t tun2
+ifconfig tun2 192.168.2.1
+@end example
+Then bob can use this interface with the option "-tun tun2". Note that
+option permit the use of a DHCP server on the host to configure the
+guest interface.
+
 @item -tun-fd fd
 Assumes @var{fd} talks to a tap/tun host network interface and use
 it. Read @url{http://bellard.org/qemu/tetrinet.html} to have an
Index: vl.c
===================================================================
RCS file: /cvsroot/qemu/qemu/vl.c,v
retrieving revision 1.120
diff -u -r1.120 vl.c
--- vl.c	10 Feb 2005 22:00:06 -0000	1.120
+++ vl.c	13 Feb 2005 01:59:05 -0000
@@ -1600,7 +1600,7 @@
     }
     memset(&ifr, 0, sizeof(ifr));
     ifr.ifr_flags = IFF_TAP | IFF_NO_PI;
-    pstrcpy(ifr.ifr_name, IFNAMSIZ, "tun%d");
+    pstrcpy(ifr.ifr_name, IFNAMSIZ, (ifname && *ifname) ? ifname : "tun%d");
     ret = ioctl(fd, TUNSETIFF, (void *) &ifr);
     if (ret != 0) {
         fprintf(stderr, "warning: could not configure /dev/net/tun: no virtual network emulation\n");
@@ -1626,7 +1626,7 @@
     qemu_add_fd_read_handler(nd->fd, fd_can_read, fd_read, opaque);
 }
 
-static int net_tun_init(NetDriverState *nd)
+static int net_tun_init(NetDriverState *nd, int script)
 {
     int pid, status;
     char *args[3];
@@ -1637,7 +1637,7 @@
         return -1;
 
     /* try to launch network init script */
-    pid = fork();
+    pid = script ? fork() : -1;
     if (pid >= 0) {
         if (pid == 0) {
             parg = args;
@@ -2731,6 +2731,7 @@
            "-nics n         simulate 'n' network cards [default=1]\n"
            "-macaddr addr   set the mac address of the first interface\n"
            "-n script       set tap/tun network init script [default=%s]\n"
+           "-tun devname    try to use devname while opening tap/tun interface\n"
            "-tun-fd fd      use this fd as already opened tap/tun interface\n"
 #ifdef CONFIG_SLIRP
            "-user-net       use user mode network stack [default if no tap/tun script]\n"
@@ -2819,6 +2820,7 @@
     QEMU_OPTION_nics,
     QEMU_OPTION_macaddr,
     QEMU_OPTION_n,
+    QEMU_OPTION_tun,
     QEMU_OPTION_tun_fd,
     QEMU_OPTION_user_net,
     QEMU_OPTION_tftp,
@@ -2880,6 +2882,7 @@
     { "nics", HAS_ARG, QEMU_OPTION_nics},
     { "macaddr", HAS_ARG, QEMU_OPTION_macaddr},
     { "n", HAS_ARG, QEMU_OPTION_n },
+    { "tun", HAS_ARG, QEMU_OPTION_tun },
     { "tun-fd", HAS_ARG, QEMU_OPTION_tun_fd },
 #ifdef CONFIG_SLIRP
     { "user-net", 0, QEMU_OPTION_user_net },
@@ -2990,7 +2993,7 @@
     int cyls, heads, secs, translation;
     int start_emulation = 1;
     uint8_t macaddr[6];
-    int net_if_type, nb_tun_fds, tun_fds[MAX_NICS];
+    int net_if_type, nb_tun, nb_tun_fds, cnt_tun_fds, tun_fds[MAX_NICS];
     int optind;
     const char *r, *optarg;
     CharDriverState *monitor_hd;
@@ -3037,7 +3040,12 @@
         parallel_devices[i][0] = '\0';
     parallel_device_index = 0;
     
+    for(i = 0; i < MAX_NICS; i++) {
+	nd_table[i].ifname[0] = '\0';
+    }
+    nb_tun = 0;
     nb_tun_fds = 0;
+    cnt_tun_fds = 0;
     net_if_type = -1;
     nb_nics = 1;
     /* default mac address of the first network interface */
@@ -3141,18 +3149,25 @@
             case QEMU_OPTION_append:
                 kernel_cmdline = optarg;
                 break;
+	    case QEMU_OPTION_tun:
+		net_if_type = NET_IF_TUN;
+		if (nb_tun+nb_tun_fds < MAX_NICS) {
+		    pstrcpy(nd_table[nb_tun++].ifname, IFNAMSIZ, optarg);
+		}
+		break;
 	    case QEMU_OPTION_tun_fd:
                 {
                     const char *p;
                     int fd;
                     net_if_type = NET_IF_TUN;
-                    if (nb_tun_fds < MAX_NICS) {
+                    if (nb_tun+nb_tun_fds < MAX_NICS) {
                         fd = strtol(optarg, (char **)&p, 0);
                         if (*p != '\0') {
                             fprintf(stderr, "qemu: invalid fd for network interface %d\n", nb_tun_fds);
                             exit(1);
                         }
                         tun_fds[nb_tun_fds++] = fd;
+			nb_tun++;
                     }
                 }
 		break;
@@ -3426,12 +3441,20 @@
 #endif
 #if !defined(_WIN32)
         case NET_IF_TUN:
-            if (i < nb_tun_fds) {
-                net_fd_init(nd, tun_fds[i]);
-            } else {
-                if (net_tun_init(nd) < 0)
-                    net_dummy_init(nd);
-            }
+	    if (nd->ifname && *(nd->ifname)) {
+		if (net_tun_init(nd, 0) < 0) {
+		    nd->ifname[0] = '\0';
+		    if (net_tun_init(nd, 1) < 0)
+		      net_dummy_init(nd);
+		}
+	    } else {
+		if (cnt_tun_fds < nb_tun_fds) {
+		    net_fd_init(nd, tun_fds[cnt_tun_fds++]);
+		} else {
+		    if (net_tun_init(nd, 1) < 0)
+		      net_dummy_init(nd);
+		}
+	    }
             break;
 #endif
         case NET_IF_DUMMY: