net/tap: Factorize fd closing after forking

The same code is used twice to actually close all open file descriptors
after forking. Factorize it in a single place.

Signed-off-by: Clément Léger <cleger@rivosinc.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20240802145423.3232974-4-cleger@rivosinc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

net/tap.c

@@ -385,6 +385,17 @@ static TAPState *net_tap_fd_init(NetClientState *peer,
     return s;
 }
 
+static void close_all_fds_after_fork(int excluded_fd)
+{
+    int open_max = sysconf(_SC_OPEN_MAX), i;
+
+    for (i = 3; i < open_max; i++) {
+        if (i != excluded_fd) {
+            close(i);
+        }
+    }
+}
+
 static void launch_script(const char *setup_script, const char *ifname,
                           int fd, Error **errp)
 {
@@ -400,13 +411,7 @@ static void launch_script(const char *setup_script, const char *ifname,
         return;
     }
     if (pid == 0) {
-        int open_max = sysconf(_SC_OPEN_MAX), i;
-
-        for (i = 3; i < open_max; i++) {
-            if (i != fd) {
-                close(i);
-            }
-        }
+        close_all_fds_after_fork(fd);
         parg = args;
         *parg++ = (char *)setup_script;
         *parg++ = (char *)ifname;
@@ -490,17 +495,11 @@ static int net_bridge_run_helper(const char *helper, const char *bridge,
         return -1;
     }
     if (pid == 0) {
-        int open_max = sysconf(_SC_OPEN_MAX), i;
         char *fd_buf = NULL;
         char *br_buf = NULL;
         char *helper_cmd = NULL;
 
-        for (i = 3; i < open_max; i++) {
-            if (i != sv[1]) {
-                close(i);
-            }
-        }
-
+        close_all_fds_after_fork(sv[1]);
         fd_buf = g_strdup_printf("%s%d", "--fd=", sv[1]);
 
         if (strrchr(helper, ' ') || strrchr(helper, '\t')) {