[PATCH] Reordering how tap is initialized

[Stephane Bakhos <nuitari-kvm@xxxxxxxxxxx>]

This is my first patch, so I apoligize for breaking any convention.

This patch modifies the order used in net.c for tap initialization.
It runs the script before the device is opened. This permits the creation 
of the tap device via a script instead of having to do it in advance.

It also waits for the tap to be closed before running the down script, as 
this permits the destruction of the tap device afterwards.

It applies to git and kvm-88

diff --git a/net.c b/net.c
index 1e845cf..afbb0f2 100644
--- a/net.c
+++ b/net.c
@@ -1295,7 +1295,7 @@ typedef struct TAPState {
     unsigned int using_vnet_hdr : 1;
 } TAPState;
 
-static int launch_script(const char *setup_script, const char *ifname, int fd);
+static int launch_script(const char *setup_script, const char *ifname);
 
 static int tap_can_send(void *opaque);
 static void tap_send(void *opaque);
@@ -1557,12 +1557,13 @@ static void tap_cleanup(VLANClientState *vc)
 
     qemu_purge_queued_packets(vc);
 
-    if (s->down_script[0])
-        launch_script(s->down_script, s->down_script_arg, s->fd);
-
     tap_read_poll(s, 0);
     tap_write_poll(s, 0);
     close(s->fd);
+
+    if (s->down_script[0])
+        launch_script(s->down_script, s->down_script_arg);
+
     qemu_free(s);
 }
 
@@ -1794,7 +1795,7 @@ static int tap_open(char *ifname, int ifname_size, int *vnet_hdr)
 }
 #endif
 
-static int launch_script(const char *setup_script, const char *ifname, int fd)
+static int launch_script(const char *setup_script, const char *ifname)
 {
     sigset_t oldmask, mask;
     int pid, status;
@@ -1813,8 +1814,7 @@ static int launch_script(const char *setup_script, const char *ifname, int fd)
         for (i = 0; i < open_max; i++) {
             if (i != STDIN_FILENO &&
                 i != STDOUT_FILENO &&
-                i != STDERR_FILENO &&
-                i != fd) {
+                i != STDERR_FILENO) {
                 close(i);
             }
         }
@@ -1852,16 +1852,18 @@ static TAPState *net_tap_init(VLANState *vlan, const char *model,
     else
         ifname[0] = '\0';
     vnet_hdr = 0;
-    TFR(fd = tap_open(ifname, sizeof(ifname), &vnet_hdr));
-    if (fd < 0)
-        return NULL;
 
     if (!setup_script || !strcmp(setup_script, "no"))
         setup_script = "";
     if (setup_script[0] != '\0' &&
-        launch_script(setup_script, ifname, fd)) {
+        launch_script(setup_script, ifname)) {
         return NULL;
     }
+
+    TFR(fd = tap_open(ifname, sizeof(ifname), &vnet_hdr));
+    if (fd < 0)
+        return NULL;
+
     s = net_tap_fd_init(vlan, model, name, fd, vnet_hdr);
     snprintf(s->vc->info_str, sizeof(s->vc->info_str),
              "ifname=%s,script=%s,downscript=%s",