Re: [PATCH 3/3] selftests/cachestat: add an overlayfs test case

[Pavel Tikhomirov <ptikhomirov@virtuozzo.com>]

On 6/23/26 18:13, Nhat Pham wrote:
> On Tue, Jun 23, 2026 at 4:15 AM Pavel Tikhomirov
> <ptikhomirov@virtuozzo.com> wrote:
>>
>> Mount an overlayfs, create and write a file in the merged directory, and
>> run cachestat() on it, reusing the existing test_cachestat() helper.
>>
>> Also bump NR_TESTS to the actual number of tests run: it was 9 while
>> ten tests were already executed, and this adds an eleventh.
>>
>> Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
>> ---
>>  .../selftests/cachestat/test_cachestat.c      | 75 ++++++++++++++++++-
> 
> Hmm this looks strange...?

That's just how git-format-patch formats it for long path and big
change ("++...++") it hides part of the path.

> 
>>  1 file changed, 74 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/testing/selftests/cachestat/test_cachestat.c b/tools/testing/selftests/cachestat/test_cachestat.c
>> index 542cd09cb4434..1662d9817c50b 100644
>> --- a/tools/testing/selftests/cachestat/test_cachestat.c
>> +++ b/tools/testing/selftests/cachestat/test_cachestat.c
>> @@ -4,21 +4,25 @@
>>
>>  #include <stdio.h>
>>  #include <stdbool.h>
>> +#include <stdlib.h>
>>  #include <linux/kernel.h>
>>  #include <linux/magic.h>
>>  #include <linux/mman.h>
>>  #include <sys/mman.h>
>> +#include <sys/mount.h>
>>  #include <sys/shm.h>
>> +#include <sys/stat.h>
>>  #include <sys/syscall.h>
>>  #include <sys/vfs.h>
>>  #include <unistd.h>
>>  #include <string.h>
>>  #include <fcntl.h>
>>  #include <errno.h>
>> +#include <limits.h>
>>
>>  #include "kselftest.h"
>>
>> -#define NR_TESTS       9
>> +#define NR_TESTS       11
>>
>>  static const char * const dev_files[] = {
>>         "/dev/zero", "/dev/null", "/dev/urandom",
>> @@ -294,6 +298,62 @@ bool run_cachestat_test(enum file_type type)
>>         return ret;
>>  }
>>
>> +/*
>> + * Set up an overlayfs mount and run cachestat on a freshly created file in the
>> + * merged directory. Overlayfs forwards data I/O to the underlying (upper)
>> + * inode, so the page cache lives there and not in the overlay inode's mapping.
>> + * This is a regression test for cachestat returning all zeroes on overlayfs.
>> + */
>> +static int run_cachestat_overlayfs_test(void)
>> +{
>> +       char tmpl[] = "/tmp/cachestat_ovl.XXXXXX";
>> +       char lower[PATH_MAX], upper[PATH_MAX], work[PATH_MAX];
>> +       char merged[PATH_MAX], opts[4 * PATH_MAX], file[PATH_MAX];
>> +       char *base;
>> +       int ret;
>> +
>> +       base = mkdtemp(tmpl);
>> +       if (!base) {
>> +               ksft_print_msg("Unable to create overlayfs base dir: %s\n",
>> +                              strerror(errno));
>> +               return KSFT_FAIL;
>> +       }
>> +
>> +       snprintf(lower, sizeof(lower), "%s/lower", base);
>> +       snprintf(upper, sizeof(upper), "%s/upper", base);
>> +       snprintf(work, sizeof(work), "%s/work", base);
>> +       snprintf(merged, sizeof(merged), "%s/merged", base);
>> +
>> +       if (mkdir(lower, 0755) || mkdir(upper, 0755) ||
>> +           mkdir(work, 0755) || mkdir(merged, 0755)) {
>> +               ksft_print_msg("Unable to create overlayfs dirs: %s\n",
>> +                              strerror(errno));
>> +               ret = KSFT_FAIL;
>> +               goto cleanup;
>> +       }
>> +
>> +       snprintf(opts, sizeof(opts), "lowerdir=%s,upperdir=%s,workdir=%s",
>> +                lower, upper, work);
>> +
>> +       if (mount("overlay", merged, "overlay", 0, opts)) {
>> +               ksft_print_msg("Unable to mount overlayfs (need root?): %s\n",
>> +                              strerror(errno));
>> +               ret = KSFT_SKIP;
>> +               goto cleanup;
>> +       }
>> +
>> +       snprintf(file, sizeof(file), "%s/merged/cachestat", base);
>> +       ret = test_cachestat(file, true, true, false, 4, O_CREAT | O_RDWR, 0600);
>> +
>> +       umount(merged);
>> +cleanup:
>> +       /* Best-effort recursive cleanup of the temporary tree. */
>> +       snprintf(opts, sizeof(opts), "rm -rf %s", base);
>> +       if (system(opts))
>> +               ksft_print_msg("Unable to clean up %s\n", base);
> 
> nit: no helper for these? :)

This is similar to e.g. ./tools/testing/selftests/bpf/prog_tests/test_local_storage.c's
cleanup, I didn't find a common selftest helper for temporary directory removal.

> 
>> +       return ret;
>> +}
>> +
>>  int main(void)
>>  {
>>         int ret;
>> @@ -361,5 +421,18 @@ int main(void)
>>                 ksft_test_result_fail("cachestat fails with a mmap file\n");
>>                 ret = 1;
>>         }
>> +
>> +       switch (run_cachestat_overlayfs_test()) {
>> +       case KSFT_FAIL:
>> +               ksft_test_result_fail("cachestat fails with an overlayfs file\n");
>> +               ret = 1;
>> +               break;
>> +       case KSFT_PASS:
>> +               ksft_test_result_pass("cachestat works with an overlayfs file\n");
>> +               break;
>> +       case KSFT_SKIP:
>> +               ksft_test_result_skip("overlayfs not available\n");
>> +               break;
>> +       }
>>         return ret;
>>  }
>> --
>> 2.54.0
>>

-- 
Best regards, Pavel Tikhomirov
Senior Software Developer, Virtuozzo.