[PATCH v6 6/6] selftests: prctl: Add test for long thread names

["André Almeida" <andrealmeid@igalia.com>]

Add tests for the new interface to set and get long thread names. The
kernel should accept the LONG_NAME and returning it accordingly. For the
old PR_GET_NAME interface, the kernel should truncate the name up to 16
chars. /proc/<task>/comm should return the same string ad PR_GET_NAME.

While here, fix the check_is_name_correct() logic. It currently returns 1
for success, or a negative number for error. EXPECT_TRUE() evaluates any
non-zero value as true, so the error will be evaluated as a success. Make
the logic more robust and straightforward by returning the results of
strcmp() and expecting zero as success.

Signed-off-by: André Almeida <andrealmeid@igalia.com>
---
Changes in v5:
 - fix check_is_name_correct() return logic
---
 tools/testing/selftests/prctl/set-process-name.c | 53 +++++++++++++++++++++---
 1 file changed, 48 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/prctl/set-process-name.c b/tools/testing/selftests/prctl/set-process-name.c
index 3f7b146d36df..27a0dbbce4db 100644
--- a/tools/testing/selftests/prctl/set-process-name.c
+++ b/tools/testing/selftests/prctl/set-process-name.c
@@ -9,9 +9,17 @@
 
 #include "kselftest_harness.h"
 
+#ifndef PR_SET_EXT_NAME
+# define PR_SET_EXT_NAME 17
+# define PR_GET_EXT_NAME 18
+#endif
+
 #define CHANGE_NAME "changename"
+#define LONG_NAME	"change_to_very_long_extended_name"
+#define LONG_NAME_CAP	"change_to_very_"
 #define EMPTY_NAME ""
 #define TASK_COMM_LEN 16
+#define TASK_COMM_EXT_LEN 64
 #define MAX_PATH_LEN 50
 
 int set_name(char *name)
@@ -25,6 +33,20 @@ int set_name(char *name)
 	return res;
 }
 
+int set_ext_name(char *name)
+{
+	int res;
+
+	res = prctl(PR_SET_EXT_NAME, name, NULL, NULL, NULL);
+
+	if (res < 0)
+		return -errno;
+	return res;
+}
+
+/*
+ * Return 0 if strings match
+ */
 int check_is_name_correct(char *check_name)
 {
 	char name[TASK_COMM_LEN];
@@ -35,7 +57,23 @@ int check_is_name_correct(char *check_name)
 	if (res < 0)
 		return -errno;
 
-	return !strcmp(name, check_name);
+	return strcmp(name, check_name);
+}
+
+/*
+ * Return 0 if strings match
+ */
+int check_is_ext_name_correct(char *check_name)
+{
+	char name[TASK_COMM_EXT_LEN];
+	int res;
+
+	res = prctl(PR_GET_EXT_NAME, name, NULL, NULL, NULL);
+
+	if (res < 0)
+		return -errno;
+
+	return strcmp(name, check_name);
 }
 
 int check_null_pointer(char *check_name)
@@ -56,8 +94,8 @@ int check_name(void)
 	pid = getpid();
 	FILE *fptr = NULL;
 	char path[MAX_PATH_LEN] = {};
-	char name[TASK_COMM_LEN] = {};
-	char output[TASK_COMM_LEN] = {};
+	char name[TASK_COMM_EXT_LEN] = {};
+	char output[TASK_COMM_EXT_LEN] = {};
 	int j;
 
 	j = snprintf(path, MAX_PATH_LEN, "/proc/self/task/%d/comm", pid);
@@ -80,10 +118,15 @@ int check_name(void)
 TEST(rename_process) {
 
 	EXPECT_GE(set_name(CHANGE_NAME), 0);
-	EXPECT_TRUE(check_is_name_correct(CHANGE_NAME));
+	EXPECT_FALSE(check_is_name_correct(CHANGE_NAME));
+
+	EXPECT_GE(set_ext_name(LONG_NAME), 0);
+	EXPECT_FALSE(check_is_ext_name_correct(LONG_NAME));
+	EXPECT_FALSE(check_is_name_correct(LONG_NAME_CAP));
+	EXPECT_TRUE(check_name());
 
 	EXPECT_GE(set_name(EMPTY_NAME), 0);
-	EXPECT_TRUE(check_is_name_correct(EMPTY_NAME));
+	EXPECT_FALSE(check_is_name_correct(EMPTY_NAME));
 
 	EXPECT_GE(set_name(CHANGE_NAME), 0);
 	EXPECT_LT(check_null_pointer(CHANGE_NAME), 0);

-- 
2.55.0