[PATCH] net: tap: Drop the close of fds for child process

[Bin Meng]

Current codes using a brute-force traversal of all file descriptors
do not scale on a system where the maximum number of file descriptors
are set to a very large value (e.g.: in a Docker container of Manjaro
distribution it is set to 1073741816). QEMU just looks freezed during
start-up.

The close-on-exec flag was introduced since a faily old Linux kernel
(2.6.23). With recent newer kernels that QEMU supports, we don't need
to manually close the fds for child process as the proper O_CLOEXEC
flag should have been set properly on files that we don't want child
process to see.

Reported-by: Zhangjin Wu <falcon@tinylab.org>
Signed-off-by: Bin Meng <bmeng@tinylab.org>
---

 net/tap.c | 14 --------------
 1 file changed, 14 deletions(-)

diff --git a/net/tap.c b/net/tap.c
index 1bf085d422..49e1915484 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -446,13 +446,6 @@ 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);
-            }
-        }
         parg = args;
         *parg++ = (char *)setup_script;
         *parg++ = (char *)ifname;
@@ -536,17 +529,10 @@ 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);
-            }
-        }
-
         fd_buf = g_strdup_printf("%s%d", "--fd=", sv[1]);
 
         if (strrchr(helper, ' ') || strrchr(helper, '\t')) {
-- 
2.34.1