linux-kernel - [PATCH] selftests: clarify common error when running gup

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Date:   Mon,  2 May 2022 18:49:42 -0400
From:   Joel Savitz <jsavitz@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Joel Savitz <jsavitz@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>, Nico Pache <npache@...hat.com>,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org
Subject: [PATCH] selftests: clarify common error when running gup_test


The gup_test binary will fail showing only the output of perror("open") in
the case that /sys/kernel/debug/gup_test is not found. This will almost
always be due to CONFIG_GUP_TEST not being set, which enables
compilation of a kernel that provides this file.

Add a short error message to clarify this failure and point the user to
the solution.

Signed-off-by: Joel Savitz <jsavitz@...hat.com>
---
 tools/testing/selftests/vm/gup_test.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/vm/gup_test.c b/tools/testing/selftests/vm/gup_test.c
index cda837a14736..ac4e804d47f0 100644
--- a/tools/testing/selftests/vm/gup_test.c
+++ b/tools/testing/selftests/vm/gup_test.c
@@ -18,6 +18,8 @@
 #define FOLL_WRITE	0x01	/* check pte is writable */
 #define FOLL_TOUCH	0x02	/* mark page accessed */
 
+#define GUP_TEST_FILE "/sys/kernel/debug/gup_test"
+
 static unsigned long cmd = GUP_FAST_BENCHMARK;
 static int gup_fd, repeats = 1;
 static unsigned long size = 128 * MB;
@@ -204,9 +206,11 @@ int main(int argc, char **argv)
 	if (write)
 		gup.gup_flags |= FOLL_WRITE;
 
-	gup_fd = open("/sys/kernel/debug/gup_test", O_RDWR);
+	gup_fd = open(GUP_TEST_FILE, O_RDWR);
 	if (gup_fd == -1) {
 		perror("open");
+		fprintf(stderr, "Unable to open %s: check that CONFIG_GUP_TEST=y\n",
+				GUP_TEST_FILE);
 		exit(1);
 	}
 
-- 
2.27.0