[PATCH v2 1/2] selftests: cachestat: add tests for mmap

[Suresh K C <suresh.k.chandrappa@gmail.com>]

From: Suresh K C <suresh.k.chandrappa@gmail.com>

Add a test case to verify cachestat behavior with memory-mapped files
using mmap(). This ensures that pages accessed via mmap are correctly
accounted for in the page cache.

Tested on x86_64 with default kernel config

Signed-off-by: Suresh K C <suresh.k.chandrappa@gmail.com>
---
 .../selftests/cachestat/test_cachestat.c      | 39 ++++++++++++++++---
 1 file changed, 33 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/cachestat/test_cachestat.c b/tools/testing/selftests/cachestat/test_cachestat.c
index 632ab44737ec..b6452978dae0 100644
--- a/tools/testing/selftests/cachestat/test_cachestat.c
+++ b/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);
@@ -202,7 +207,7 @@ static int test_cachestat(const char *filename, bool write_random, bool create,
 	return ret;
 }
 
-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 +217,43 @@ 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 file.\n");
 		ret = false;
 		goto out;
 	}
 
 	if (ftruncate(fd, filesize)) {
-		ksft_print_msg("Unable to truncate shmem file.\n");
+		ksft_print_msg("Unable to truncate file.\n");
 		ret = false;
 		goto close_fd;
 	}
 
 	if (!write_exactly(fd, filesize)) {
-		ksft_print_msg("Unable to write to shmem file.\n");
+		ksft_print_msg("Unable to write to file.\n");
 		ret = false;
 		goto close_fd;
 	}
 
+	if (type == 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';
+		}
+		map[filesize - 1] = 'X';
+	}
 	syscall_ret = syscall(__NR_cachestat, fd, &cs_range, &cs, 0);
 
 	if (syscall_ret) {
@@ -308,12 +329,18 @@ 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;
 }
-- 
2.43.0