selftests: cachestat: add tests for mmap, refactor and enhance mmap test for cachestat validation

Add a cohesive test case that verifies cachestat behavior with
memory-mapped files using mmap().  Also refactor the test logic to reduce
redundancy, improve error reporting, and clarify failure messages for both
shmem and mmap file types.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Suresh K C <[email protected]>
Reviewed-by: Joshua Hahn <[email protected]>
Tested-by: Nhat Pham <[email protected]>
Acked-by: Nhat Pham <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Shuah Khan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: SureshChandrappa

tools/testing/selftests/cachestat/test_cachestat.c

@@ -33,6 +33,11 @@ void print_cachestat(struct cachestat *cs)
 	cs->nr_evicted, cs->nr_recently_evicted);
 }
 
+enum file_type {
+	FILE_MMAP,
+	FILE_SHMEM
+};
+
 bool write_exactly(int fd, size_t filesize)
 {
 	int random_fd = open("/dev/urandom", O_RDONLY);
@@ -201,8 +206,19 @@ static int test_cachestat(const char *filename, bool write_random, bool create,
 out:
 	return ret;
 }
+const char* file_type_str(enum file_type type) {
+	switch (type) {
+		case FILE_SHMEM:
+			return "shmem";
+		case FILE_MMAP:
+			return "mmap";
+		default:
+			return "unknown";
+	}
+}
 
-bool test_cachestat_shmem(void)
+
+bool run_cachestat_test(enum file_type type)
 {
 	size_t PS = sysconf(_SC_PAGESIZE);
 	size_t filesize = PS * 512 * 2; /* 2 2MB huge pages */
@@ -212,27 +228,49 @@ bool test_cachestat_shmem(void)
 	char *filename = "tmpshmcstat";
 	struct cachestat cs;
 	bool ret = true;
+	int fd;
 	unsigned long num_pages = compute_len / PS;
-	int fd = shm_open(filename, O_CREAT | O_RDWR, 0600);
+	if (type == FILE_SHMEM)
+		fd = shm_open(filename, O_CREAT | O_RDWR, 0600);
+	else
+		fd = open(filename, O_RDWR | O_CREAT | O_TRUNC, 0666);
 
 	if (fd < 0) {
-		ksft_print_msg("Unable to create shmem file.\n");
+		ksft_print_msg("Unable to create %s file.\n",file_type_str(type));
 		ret = false;
 		goto out;
 	}
 
 	if (ftruncate(fd, filesize)) {
-		ksft_print_msg("Unable to truncate shmem file.\n");
+		ksft_print_msg("Unable to truncate %s file.\n",file_type_str(type));
 		ret = false;
 		goto close_fd;
 	}
-
-	if (!write_exactly(fd, filesize)) {
-		ksft_print_msg("Unable to write to shmem file.\n");
-		ret = false;
-		goto close_fd;
+	switch (type){
+		case FILE_SHMEM:
+			if (!write_exactly(fd, filesize)) {
+				ksft_print_msg("Unable to write to file.\n");
+				ret = false;
+				goto close_fd;
+			}
+			break;
+		case FILE_MMAP:
+			char *map = mmap(NULL, filesize, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+			if (map == MAP_FAILED) {
+				ksft_print_msg("mmap failed.\n");
+				ret = false;
+				goto close_fd;
+			}
+			for (int i = 0; i < filesize; i++) {
+				map[i] = 'A';
+			}
+			break;
+		default:
+			ksft_print_msg("Unsupported file type.\n");
+			ret = false;
+			goto close_fd;
+			break;
 	}
-
 	syscall_ret = syscall(__NR_cachestat, fd, &cs_range, &cs, 0);
 
 	if (syscall_ret) {
@@ -308,12 +346,18 @@ int main(void)
 		break;
 	}
 
-	if (test_cachestat_shmem())
+	if (run_cachestat_test(FILE_SHMEM))
 		ksft_test_result_pass("cachestat works with a shmem file\n");
 	else {
 		ksft_test_result_fail("cachestat fails with a shmem file\n");
 		ret = 1;
 	}
 
+	if (run_cachestat_test(FILE_MMAP))
+		ksft_test_result_pass("cachestat works with a mmap file\n");
+	else {
+		ksft_test_result_fail("cachestat fails with a mmap file\n");
+		ret = 1;
+	}
 	return ret;
 }