tools/testing/selftests/vm/gup_test.c: clarify error statement

Print three possible reasons /sys/kernel/debug/gup_test cannot be opened
to help users of this test diagnose failures.

Link: https://lkml.kernel.org/r/20220405214809.3351223-1-sidhartha.kumar@oracle.comSigned-off-by: NSidhartha Kumar <sidhartha.kumar@oracle.com>
Reviewed-by: NShuah Khan <skhan@linuxfoundation.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/vm/gup_test.c

 #include <fcntl.h>
+#include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
+#include <dirent.h>
 #include <sys/ioctl.h>
 #include <sys/mman.h>
 #include <sys/stat.h>
@@ -9,6 +11,7 @@
 #include <pthread.h>
 #include <assert.h>
 #include "../../../../mm/gup_test.h"
+#include "../kselftest.h"
 
 #include "util.h"
 
@@ -206,8 +209,23 @@ int main(int argc, char **argv)
 
 	gup_fd = open("/sys/kernel/debug/gup_test", O_RDWR);
 	if (gup_fd == -1) {
-		perror("open");
-		exit(1);
+		switch (errno) {
+		case EACCES:
+			if (getuid())
+				printf("Please run this test as root\n");
+			break;
+		case ENOENT:
+			if (opendir("/sys/kernel/debug") == NULL) {
+				printf("mount debugfs at /sys/kernel/debug\n");
+				break;
+			}
+			printf("check if CONFIG_GUP_TEST is enabled in kernel config\n");
+			break;
+		default:
+			perror("failed to open /sys/kernel/debug/gup_test");
+			break;
+		}
+		exit(KSFT_SKIP);
 	}
 
 	p = mmap(NULL, size, PROT_READ | PROT_WRITE, flags, filed, 0);

tools/testing/selftests/vm/run_vmtests.sh

@@ -162,22 +162,32 @@ echo "------------------------------------------------------"
 echo "running: gup_test -u # get_user_pages_fast() benchmark"
 echo "------------------------------------------------------"
 ./gup_test -u
-if [ $? -ne 0 ]; then
+ret_val=$?
+
+if [ $ret_val -eq 0 ]; then
+	echo "[PASS]"
+elif [ $ret_val -eq $ksft_skip ]; then
+	 echo "[SKIP]"
+	 exitcode=$ksft_skip
+else
 	echo "[FAIL]"
 	exitcode=1
-else
-	echo "[PASS]"
 fi
 
 echo "------------------------------------------------------"
 echo "running: gup_test -a # pin_user_pages_fast() benchmark"
 echo "------------------------------------------------------"
 ./gup_test -a
-if [ $? -ne 0 ]; then
+ret_val=$?
+
+if [ $ret_val -eq 0 ]; then
+	echo "[PASS]"
+elif [ $ret_val -eq $ksft_skip ]; then
+	 echo "[SKIP]"
+	 exitcode=$ksft_skip
+else
 	echo "[FAIL]"
 	exitcode=1
-else
-	echo "[PASS]"
 fi
 
 echo "------------------------------------------------------------"
@@ -185,11 +195,16 @@ echo "# Dump pages 0, 19, and 4096, using pin_user_pages:"
 echo "running: gup_test -ct -F 0x1 0 19 0x1000 # dump_page() test"
 echo "------------------------------------------------------------"
 ./gup_test -ct -F 0x1 0 19 0x1000
-if [ $? -ne 0 ]; then
+ret_val=$?
+
+if [ $ret_val -eq 0 ]; then
+	echo "[PASS]"
+elif [ $ret_val -eq $ksft_skip ]; then
+	 echo "[SKIP]"
+	 exitcode=$ksft_skip
+else
 	echo "[FAIL]"
 	exitcode=1
-else
-	echo "[PASS]"
 fi
 
 echo "-------------------"