Use POSIX fcntl(F_DUPFD_CLOEXEC) instead of Linux dup3()

As an added bonus, we don't need to open /dev/null for nothing.

configure.ac

@@ -557,7 +557,7 @@ AC_CHECK_FUNCS(fdatasync,,
 AC_FUNC_STRCOLL
 
 dnl Check for non-standard system calls
-AC_CHECK_FUNCS([accept4 dup3 pipe2 eventfd vmsplice sched_getaffinity])
+AC_CHECK_FUNCS([accept4 pipe2 eventfd vmsplice sched_getaffinity])
 
 AH_BOTTOM([#include <vlc_fixups.h>])
 

src/posix/filesystem.c

@@ -315,22 +315,15 @@ int vlc_dup (int oldfd)
 {
     int newfd;
 
-#ifdef HAVE_DUP3
-    /* Unfortunately, dup3() works like dup2(), not like plain dup(). So we
-     * need such contortion to find the new file descriptor while preserving
-     * thread safety of the file descriptor table. */
-    newfd = vlc_open ("/dev/null", O_RDONLY);
-    if (likely(newfd != -1))
-    {
-        if (likely(dup3 (oldfd, newfd, O_CLOEXEC) == newfd))
-            return newfd;
-        close (newfd);
-    }
+#ifdef F_DUPFD_CLOEXEC
+    newfd = fcntl (oldfd, F_DUPFD_CLOEXEC);
+    if (unlikely(newfd == -1 && errno == EINVAL))
 #endif
-
+    {
         newfd = dup (oldfd);
         if (likely(newfd != -1))
             fcntl (newfd, F_SETFD, FD_CLOEXEC);
+    }
     return newfd;
 }