net/tap: rework scripts handling

Simplify handling scripts: parse all these "no" and '\0' once, and
then keep simpler logic for net_tap_open() and net_init_tap_one(): NULL
means no script to run, otherwise run script.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: Maksim Davydov <davydov-max@yandex-team.ru>
Signed-off-by: Jason Wang <jasowang@redhat.com>

net/tap.c

diff --git a/net/tap.c b/net/tap.c
index 8182f39..c7d8e1a 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -91,6 +91,21 @@
 static void tap_send(void *opaque);
 static void tap_writable(void *opaque);
 
+static char *tap_parse_script(const char *script_arg, const char *default_path)
+{
+    g_autofree char *res = g_strdup(script_arg);
+
+    if (!res) {
+        res = get_relocated_path(default_path);
+    }
+
+    if (res[0] == '\0' || strcmp(res, "no") == 0) {
+        return NULL;
+    }
+
+    return g_steal_pointer(&res);
+}
+
 static void tap_update_fd_handler(TAPState *s)
 {
     qemu_set_fd_handler(s->fd,
@@ -676,9 +691,7 @@
         return -1;
     }
 
-    if (setup_script &&
-        setup_script[0] != '\0' &&
-        strcmp(setup_script, "no") != 0) {
+    if (setup_script) {
         launch_script(setup_script, ifname, fd, &err);
         if (err) {
             error_propagate(errp, err);
@@ -714,9 +727,9 @@
         qemu_set_info_str(&s->nc, "helper=%s", tap->helper);
     } else {
         qemu_set_info_str(&s->nc, "ifname=%s,script=%s,downscript=%s", ifname,
-                          script, downscript);
+                          script ?: "no", downscript ?: "no");
 
-        if (strcmp(downscript, "no") != 0) {
+        if (downscript) {
             snprintf(s->down_script, sizeof(s->down_script), "%s", downscript);
             snprintf(s->down_script_arg, sizeof(s->down_script_arg),
                      "%s", ifname);
@@ -970,23 +983,16 @@
             return -1;
         }
     } else {
-        const char *script = tap->script;
-        const char *downscript = tap->downscript;
-        g_autofree char *default_script = NULL;
-        g_autofree char *default_downscript = NULL;
+        g_autofree char *script =
+            tap_parse_script(tap->script, DEFAULT_NETWORK_SCRIPT);
+        g_autofree char *downscript =
+            tap_parse_script(tap->downscript, DEFAULT_NETWORK_DOWN_SCRIPT);
+
         if (tap->vhostfds) {
             error_setg(errp, "vhostfds= is invalid if fds= wasn't specified");
             return -1;
         }
 
-        if (!script) {
-            script = default_script = get_relocated_path(DEFAULT_NETWORK_SCRIPT);
-        }
-        if (!downscript) {
-            downscript = default_downscript =
-                                 get_relocated_path(DEFAULT_NETWORK_DOWN_SCRIPT);
-        }
-
         if (tap->ifname) {
             pstrcpy(ifname, sizeof ifname, tap->ifname);
         } else {
@@ -994,7 +1000,7 @@
         }
 
         for (i = 0; i < queues; i++) {
-            fd = net_tap_init(tap, &vnet_hdr, i >= 1 ? "no" : script,
+            fd = net_tap_init(tap, &vnet_hdr, i >= 1 ? NULL : script,
                               ifname, sizeof ifname, queues > 1, errp);
             if (fd == -1) {
                 return -1;
@@ -1009,8 +1015,8 @@
             }
 
             net_init_tap_one(tap, peer, "tap", name, ifname,
-                             i >= 1 ? "no" : script,
-                             i >= 1 ? "no" : downscript,
+                             i >= 1 ? NULL : script,
+                             i >= 1 ? NULL : downscript,
                              vhostfdname, vnet_hdr, fd, &err);
             if (err) {
                 error_propagate(errp, err);