fcntl: use to simplify other modules Let fcntl do the work, instead of copying code into other modules. * modules/cloexec (Depends-on): Add fcntl. * modules/fchdir (Depends-on): Likewise. * modules/fd-safer-flag (Depends-on): Likewise. * modules/unistd-safer (Depends-on): Likewise. * modules/dup3 (configure.ac): Set module indicator. * m4/fchdir.m4 (gl_FUNC_FCHDIR): Replace fcntl if fchdir is missing. * lib/fchdir.c (_gl_register_dup): Fix comment. * lib/cloexec.c (dup_cloexec): Simplify, by relying on fcntl. * lib/dup-safer.c (dup_safer): Likewise. * lib/dup-safer-flag.c (dup_safer_flag): Likewise. * lib/dup3.c (dup3): Likewise. * tests/test-fchdir.c (main): Enhance test. Fixes a dup_cloexec bug reported by Ondřej Vašík. Signed-off-by: Eric Blake <ebb9@byu.net>

--- a/tests/test-fchdir.c
+++ b/tests/test-fchdir.c
@@ -89,6 +89,15 @@
           ASSERT (dup_cloexec (fd) == new_fd);
           ASSERT (dup2 (new_fd, fd) == fd);
           ASSERT (close (new_fd) == 0);
+          ASSERT (fcntl (fd, F_DUPFD_CLOEXEC, new_fd) == new_fd);
+          ASSERT (close (fd) == 0);
+          ASSERT (fcntl (new_fd, F_DUPFD, fd) == fd);
+          ASSERT (close (new_fd) == 0);
+#if GNULIB_DUP3
+          ASSERT (dup3 (fd, new_fd, 0) == new_fd);
+          ASSERT (dup3 (new_fd, fd, 0) == fd);
+          ASSERT (close (new_fd) == 0);
+#endif
         }
     }