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

This patch adds a new test case to validate cachestat behavior with
memory-mapped files using mmap(). The test ensures that pages are
properly cached when accessed via mmap and verifies the expected
number of cached pages.

Additionally, a test case for /proc/cpuinfo has been added to observe
how cachestat handles virtual files under /proc. This helps improve
coverage of edge cases involving pseudo-filesystems

Signed-off-by: Suresh K C <suresh.k.chandrappa@gmail.com>
---
 .../selftests/cachestat/test_cachestat.c      | 69 ++++++++++++++++++-
 1 file changed, 67 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/cachestat/test_cachestat.c b/tools/testing/selftests/cachestat/test_cachestat.c
index 632ab44737ec..81e7f6dd2279 100644
--- a/tools/testing/selftests/cachestat/test_cachestat.c
+++ b/tools/testing/selftests/cachestat/test_cachestat.c
@@ -22,7 +22,7 @@

 static const char * const dev_files[] = {
        "/dev/zero", "/dev/null", "/dev/urandom",
-       "/proc/version", "/proc"
+       "/proc/version","/proc/cpuinfo","/proc"
 };

 void print_cachestat(struct cachestat *cs)
@@ -202,6 +202,65 @@ static int test_cachestat(const char *filename, bool write_random, bool create,
        return ret;
 }

+bool test_cachestat_mmap(void){
+
+       size_t PS = sysconf(_SC_PAGESIZE);
+       size_t filesize = PS * 512 * 2;;
+       int syscall_ret;
+       size_t compute_len = PS * 512;
+       struct cachestat_range cs_range = { PS, compute_len };
+       char *filename = "tmpshmcstat";
+       unsigned long num_pages = compute_len / PS;
+       struct cachestat cs;
+       bool ret = true;
+       int fd = open(filename, O_RDWR | O_CREAT | O_TRUNC, 0666);
+       if (fd < 0) {
+               ksft_print_msg("Unable to create mmap file.\n");
+               ret = false;
+               goto out;
+       }
+       if (ftruncate(fd, filesize)) {
+               ksft_print_msg("Unable to truncate mmap file.\n");
+               ret = false;
+               goto close_fd;
+       }
+       if (!write_exactly(fd, filesize)) {
+               ksft_print_msg("Unable to write to mmap file.\n");
+               ret = false;
+               goto close_fd;
+       }
+       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) {
+               ksft_print_msg("Cachestat returned non-zero.\n");
+               ret = false;
+       } else {
+               print_cachestat(&cs);
+               if (cs.nr_cache + cs.nr_evicted != num_pages) {
+                       ksft_print_msg("Total number of cached and evicted pages is off.\n");
+                       ret = false;
+               }
+       }
+
+close_fd:
+       close(fd);
+       unlink(filename);
+out:
+       return ret;
+}
+
 bool test_cachestat_shmem(void)
 {
        size_t PS = sysconf(_SC_PAGESIZE);
@@ -274,7 +333,7 @@ int main(void)
                ret = 1;
        }

-       for (int i = 0; i < 5; i++) {
+       for (int i = 0; i < 6; i++) {
                const char *dev_filename = dev_files[i];

                if (test_cachestat(dev_filename, false, false, false,
@@ -315,5 +374,11 @@ int main(void)
                ret = 1;
        }

+       if (test_cachestat_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