[LTP] [PATCH] migrate_pages02: check file exist before opening it

[Li Wang]

This test reports a warning on some special kernel (with NUMA BALANCE
disabling). The main reason is that prefix '?' makes tst_sys_conf_save
only silent ignores non-exist paths. But seems we still open it in other
places (e.g. in setup function).

  tst_sys_conf.c:58: TINFO: Path not found: '/proc/sys/kernel/numa_balancing'
  tst_test.c:1365: TINFO: Timeout per run is 0h 05m 00s
  migrate_pages02.c:279: TWARN: Failed to open FILE '/proc/sys/kernel/numa_balancing'
  migrate_pages02.c:317: TINFO: Using nodes: 0 1

Signed-off-by: Li Wang <liwang@redhat.com>
---

Notes:
    Looks like we have many tests use the prefix '?' for knob save/restore,
    but none of them check if the paths are valid when opening at other places,
    by now, I just get informed that migrate_pages02 threw a warning.
    
    I'm thinking maybe we can keep the return value of tst_sys_conf_save
    as a check condition before opening the file, but this is not fit for
    test with many paths saving:
    e.g.
        add_key05.c-	"?/proc/sys/kernel/keys/gc_delay",
        add_key05.c-	"?/proc/sys/kernel/keys/maxkeys",

 testcases/kernel/syscalls/migrate_pages/migrate_pages02.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/testcases/kernel/syscalls/migrate_pages/migrate_pages02.c b/testcases/kernel/syscalls/migrate_pages/migrate_pages02.c
index 485a1c5aa..309e707bc 100644
--- a/testcases/kernel/syscalls/migrate_pages/migrate_pages02.c
+++ b/testcases/kernel/syscalls/migrate_pages/migrate_pages02.c
@@ -37,6 +37,8 @@
  */
 #define NODE_MIN_FREEMEM (32*1024*1024)
 
+#define NUMA_BALANCING "/proc/sys/kernel/numa_balancing"
+
 #ifdef HAVE_NUMA_V2
 
 static const char nobody_uid[] = "nobody";
@@ -276,7 +278,8 @@ static void setup(void)
 	else if (tst_kvercmp(2, 6, 18) < 0)
 		tst_brk(TCONF, "2.6.18 or greater kernel required");
 
-	FILE_PRINTF("/proc/sys/kernel/numa_balancing", "0");
+	if (access(NUMA_BALANCING, F_OK) == 0)
+		FILE_PRINTF(NUMA_BALANCING, "0");
 	/*
 	 * find 2 nodes, which can hold NODE_MIN_FREEMEM bytes
 	 * The reason is that:
@@ -328,7 +331,7 @@ static struct tst_test test = {
 	.test_all = run,
 	.setup = setup,
 	.save_restore = (const char * const[]) {
-		"?/proc/sys/kernel/numa_balancing",
+		"?NUMA_BALANCING",
 		NULL,
 	},
 };
-- 
2.31.1