[PATCH v3] linux: return UNSUPPORTED from tst-mount if entering mount namespace fails

[Michael Hudson-Doyle]

Before this the test fails if run in a chroot by a non-root user:

warning: could not become root outside namespace (Operation not permitted)
../sysdeps/unix/sysv/linux/tst-mount.c:36: numeric comparison failure
   left: 1 (0x1); from: errno
  right: 19 (0x13); from: ENODEV
error: ../sysdeps/unix/sysv/linux/tst-mount.c:39: not true: fd != -1
error: ../sysdeps/unix/sysv/linux/tst-mount.c:46: not true: r != -1
error: ../sysdeps/unix/sysv/linux/tst-mount.c:48: not true: r != -1
../sysdeps/unix/sysv/linux/tst-mount.c:52: numeric comparison failure
   left: 1 (0x1); from: errno
  right: 9 (0x9); from: EBADF
error: ../sysdeps/unix/sysv/linux/tst-mount.c:55: not true: mfd != -1
../sysdeps/unix/sysv/linux/tst-mount.c:58: numeric comparison failure
   left: 1 (0x1); from: errno
  right: 2 (0x2); from: ENOENT
error: ../sysdeps/unix/sysv/linux/tst-mount.c:61: not true: r != -1
../sysdeps/unix/sysv/linux/tst-mount.c:65: numeric comparison failure
   left: 1 (0x1); from: errno
  right: 2 (0x2); from: ENOENT
error: ../sysdeps/unix/sysv/linux/tst-mount.c:68: not true: pfd != -1
error: ../sysdeps/unix/sysv/linux/tst-mount.c:75: not true: fd_tree != -1
../sysdeps/unix/sysv/linux/tst-mount.c:88: numeric comparison failure
   left: 1 (0x1); from: errno
  right: 38 (0x26); from: ENOSYS
error: 12 test failures

Checking that the test can enter a new mount namespace is more correct
than just checking the return value of support_become_root() as the test
code changes the mount namespace it runs in so running it as root on a
system that does not support mount namespaces should still skip.

Also change the test to remove the unnecessary fork.
---
v3: check support_enter_mount_namespace() return value, remove fork
v2: check support_can_chroot() rather than support_become_root return
value
---
 sysdeps/unix/sysv/linux/tst-mount.c | 25 ++++++-------------------
 1 file changed, 6 insertions(+), 19 deletions(-)

diff --git a/sysdeps/unix/sysv/linux/tst-mount.c b/sysdeps/unix/sysv/linux/tst-mount.c
index 502d7e3433..b6333a60e6 100644
--- a/sysdeps/unix/sysv/linux/tst-mount.c
+++ b/sysdeps/unix/sysv/linux/tst-mount.c
@@ -20,15 +20,18 @@
 #include <support/check.h>
 #include <support/xunistd.h>
 #include <support/namespace.h>
-#include <sys/wait.h>
 #include <sys/mount.h>
 
 _Static_assert (sizeof (struct mount_attr) == MOUNT_ATTR_SIZE_VER0,
 		"sizeof (struct mount_attr) != MOUNT_ATTR_SIZE_VER0");
 
-static void
-subprocess (void)
+static int
+do_test (void)
 {
+  support_become_root ();
+  if (!support_enter_mount_namespace ())
+    FAIL_UNSUPPORTED ("cannot enter mount namespace, skipping test");
+
   int r = fsopen ("it_should_be_not_a_valid_mount", 0);
   TEST_VERIFY_EXIT (r == -1);
   if (errno == ENOSYS)
@@ -100,20 +103,4 @@ subprocess (void)
   _exit (0);
 }
 
-static int
-do_test (void)
-{
-  support_become_root ();
-
-  pid_t pid = xfork ();
-  if (pid == 0)
-    subprocess ();
-
-  int status;
-  xwaitpid (pid, &status, 0);
-  TEST_VERIFY (WIFEXITED (status));
-
-  return 0;
-}
-
 #include <support/test-driver.c>
-- 
2.34.1