[PATCH] selftests: pidfd: Fix compiling errors and warning

[I Hsin Cheng]

When compiling selftests files under tools/testing/selftests/pidfd/ ,
some compiling errors and warnings will pop out as the following.

  CC       pidfd_fdinfo_test
pidfd_fdinfo_test.c: In function ‘child_fdinfo_nspid_test’:
pidfd_fdinfo_test.c:231:13: warning: implicit declaration of function \
‘mount’ [-Wimplicit-function-declaration]
  231 |         r = mount(NULL, "/", NULL, MS_REC | MS_PRIVATE, 0);
      |             ^~~~~
pidfd_fdinfo_test.c:231:36: error: ‘MS_REC’ undeclared \
(first use in this function)
  231 |         r = mount(NULL, "/", NULL, MS_REC | MS_PRIVATE, 0);
      |                                    ^~~~~~
pidfd_fdinfo_test.c:231:36: note: each undeclared identifier is \
reported only once for each function it appears in
pidfd_fdinfo_test.c:231:45: error: ‘MS_PRIVATE’ undeclared \
(first use in this function); did you mean ‘MAP_PRIVATE’?
  231 |         r = mount(NULL, "/", NULL, MS_REC | MS_PRIVATE, 0);
      |                                             ^~~~~~~~~~
      |                                             MAP_PRIVATE
pidfd_fdinfo_test.c:237:15: warning: implicit declaration of function \
‘umount2’; did you mean ‘SYS_umount2’? \
[-Wimplicit-function-declaration]
  237 |         (void)umount2("/proc", MNT_DETACH);
      |               ^~~~~~~
      |               SYS_umount2
pidfd_fdinfo_test.c:237:32: error: ‘MNT_DETACH’ undeclared \
(first use in this function)
  237 |         (void)umount2("/proc", MNT_DETACH);
      |                                ^~~~~~~~~~
make: *** [../lib.mk:222: \
~/linux/tools/testing/selftests/pidfd/pidfd_fdinfo_test] Error 1

Solve these errors and warnings by including header file <sys/mount.h>.

Signed-off-by: I Hsin Cheng <richard120...@gmail.com>
---
 tools/testing/selftests/pidfd/pidfd_fdinfo_test.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/testing/selftests/pidfd/pidfd_fdinfo_test.c 
b/tools/testing/selftests/pidfd/pidfd_fdinfo_test.c
index f062a986e..f718aac75 100644
--- a/tools/testing/selftests/pidfd/pidfd_fdinfo_test.c
+++ b/tools/testing/selftests/pidfd/pidfd_fdinfo_test.c
@@ -13,6 +13,7 @@
 #include <syscall.h>
 #include <sys/wait.h>
 #include <sys/mman.h>
+#include <sys/mount.h>
 
 #include "pidfd.h"
 #include "../kselftest.h"
-- 
2.43.0