On 8/15/23 09:56, Andre Przywara wrote:

Libraries should be listed last on the compiler's command line, so that the linker can look for and find still unresolved symbols. The librt library, required for the shm_* functions, was announced using CFLAGS, which puts the library *before* the source files, and fails compilation on my system: ====================== gcc -isystem /src/linux-selftests/usr/include -Wall -lrt test_cachestat.c -o /src/linux-selftests/kselftest/cachestat/test_cachestat /usr/bin/ld: /tmp/cceQWO3u.o: in function `test_cachestat_shmem': test_cachestat.c:(.text+0x890): undefined reference to `shm_open' /usr/bin/ld: test_cachestat.c:(.text+0x99c): undefined reference to `shm_unlink' collect2: error: ld returned 1 exit status make[4]: *** [../lib.mk:181: /src/linux-selftests/kselftest/cachestat/test_cachestat] Error 1 ======================

Announce the library using the LDLIBS variable, which ensures the proper ordering on the command line.

Signed-off-by: Andre Przywara andre.przywara@arm.com

tools/testing/selftests/cachestat/Makefile | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/cachestat/Makefile b/tools/testing/selftests/cachestat/Makefile index fca73aaa7d141..778b54ebb0364 100644 --- a/tools/testing/selftests/cachestat/Makefile +++ b/tools/testing/selftests/cachestat/Makefile @@ -3,6 +3,6 @@ TEST_GEN_PROGS := test_cachestat CFLAGS += $(KHDR_INCLUDES) CFLAGS += -Wall -CFLAGS += -lrt +LDLIBS += -lrt include ../lib.mk

Thank you. Applied to linux-kselftest next for Linux 6.6-rc1

thanks, -- Shuah

On Tue, Aug 15, 2023 at 8:56 AM Andre Przywara andre.przywara@arm.com wrote:

At the moment the cachestat syscall number is hard coded into the test source code. Remove that and replace it with the proper __NR_cachestat macro. That ensures compatibility should other architectures pick a different number.

Signed-off-by: Andre Przywara andre.przywara@arm.com

tools/testing/selftests/cachestat/test_cachestat.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/cachestat/test_cachestat.c b/tools/testing/selftests/cachestat/test_cachestat.c index 54d09b820ed4b..a5a4ac8dcb76c 100644 --- a/tools/testing/selftests/cachestat/test_cachestat.c +++ b/tools/testing/selftests/cachestat/test_cachestat.c @@ -19,7 +19,6 @@ static const char * const dev_files[] = { "/dev/zero", "/dev/null", "/dev/urandom", "/proc/version", "/proc" }; -static const int cachestat_nr = 451;

void print_cachestat(struct cachestat *cs) { @@ -126,7 +125,7 @@ bool test_cachestat(const char *filename, bool write_random, bool create, } }

•   syscall_ret = syscall(cachestat_nr, fd, &cs_range, &cs, 0);
  

•   syscall_ret = syscall(__NR_cachestat, fd, &cs_range, &cs, 0);
  
    ksft_print_msg("Cachestat call returned %ld\n", syscall_ret);
  
  

@@ -152,7 +151,7 @@ bool test_cachestat(const char *filename, bool write_random, bool create, ksft_print_msg("fsync fails.\n"); ret = false; } else {

•                   syscall_ret = syscall(cachestat_nr, fd, &cs_range, &cs, 0);
  

•                   syscall_ret = syscall(__NR_cachestat, fd, &cs_range, &cs, 0);
  
                    ksft_print_msg("Cachestat call (after fsync) returned %ld\n",
                            syscall_ret);
  

@@ -213,7 +212,7 @@ bool test_cachestat_shmem(void) goto close_fd; }

•   syscall_ret = syscall(cachestat_nr, fd, &cs_range, &cs, 0);
  

•   syscall_ret = syscall(__NR_cachestat, fd, &cs_range, &cs, 0);
  
    if (syscall_ret) {
            ksft_print_msg("Cachestat returned non-zero.\n");
  

-- 2.25.1

Oops something I forgot to fix. Thanks, Andre! Reviewed-by: Nhat Pham nphamcs@gmail.com

On Tue, 15 Aug 2023 16:25:54 -0700 Nhat Pham nphamcs@gmail.com wrote:

Hi Nhat,

many thanks for having a look!

On Tue, Aug 15, 2023 at 8:56 AM Andre Przywara andre.przywara@arm.com wrote:

...

As cachestat is a new syscall, it won't be available on older kernels, for instance those running on a build machine. In this case, a run reports all tests as "not ok" at the moment.

Interesting - I was under the assumption that if you backported the selftests for cachestat, you would also backport the syscall's implementation and wiring.

Well, just running the tests on the kernel you just built is only one use case. I build the tests from latest git HEAD, then copy them to a target system with some kernel running. Or I just build the tests and run them for regression testing on my build system with a distro kernel, which is Ubuntu's 5.15 flavour, in my case. The documentation explicitly mentions that selftests should work on older kernels (copying the normal userland compatibility requirements), check the second paragraph of Documentation/dev-tools/kselftest.rst.

But yeah, I guess if you build with !CONFIG_CACHESTAT_SYSCALL, these tests would fail.

...

Test for the cachestat syscall availability first, before doing further tests, and bail out early with a TAP SKIP comment.

This also uses the opportunity to add the proper TAP headers, and add one check for the syscall error handling (illegal file descriptor).

Thanks for the addition!

...

Signed-off-by: Andre Przywara andre.przywara@arm.com

.../selftests/cachestat/test_cachestat.c | 22 ++++++++++++++++++- 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/cachestat/test_cachestat.c b/tools/testing/selftests/cachestat/test_cachestat.c index a5a4ac8dcb76c..77620e7ecf562 100644 --- a/tools/testing/selftests/cachestat/test_cachestat.c +++ b/tools/testing/selftests/cachestat/test_cachestat.c @@ -15,6 +15,8 @@

#include "../kselftest.h"

+#define NR_TESTS 8

static const char * const dev_files[] = { "/dev/zero", "/dev/null", "/dev/urandom", "/proc/version", "/proc" @@ -235,7 +237,25 @@ bool test_cachestat_shmem(void)

int main(void) {

•   int ret = 0;
  

•   int ret;
  

•   ksft_print_header();
  

•   ret = syscall(__NR_cachestat, -1, NULL, NULL, 0);
  

•   if (ret == -1 && errno == ENOSYS) {  
  

nit: if (ret && errno == ENOSYS) sounds cleaner, but up to you.

Do you ever return a positive value other than 0? I think technically errno is only valid when the return value is -1, so in the error case, which I wanted to test here explicitly. Some syscall selftests (I checked landlock the other day) do very elaborate testing of the error path, trying to carefully cover all corner cases: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tool...

So this test was inspired by that, but I didn't want to go that far here ;-)

...

•           printf("1..0 # Skipped: cachestat syscall not available\n");  
  

nit: perhaps ksft_print_msg()?

Ah, yes, of course!

...

•           return KSFT_SKIP;
  

•   }
  

•   ksft_set_plan(NR_TESTS);
  

•   if (ret == -1 && errno == EBADF) {
  

•           ksft_test_result_pass("bad file descriptor recognized\n");
  

•           ret = 0;
  

•   } else {
  

•           ksft_test_result_fail("bad file descriptor ignored\n");
  

•           ret = 1;
  

•   }  
  

Nice!

...

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

-- 2.25.1

Nitpicking aside: Acked-by: Nhat Pham nphamcs@gmail.com

Thanks, I will send a v2 later, using ksft_print_msg(). But first I will try if I can detect a tmpfs instance without boiling the ocean.

Cheers, Andre

On Wed, 16 Aug 2023 11:11:49 -0600 Shuah Khan skhan@linuxfoundation.org wrote:

Hi,

On 8/15/23 09:56, Andre Przywara wrote:

...

As cachestat is a new syscall, it won't be available on older kernels, for instance those running on a build machine. In this case, a run reports all tests as "not ok" at the moment.

Test for the cachestat syscall availability first, before doing further tests, and bail out early with a TAP SKIP comment.

This also uses the opportunity to add the proper TAP headers, and add one check for the syscall error handling (illegal file descriptor).

Signed-off-by: Andre Przywara andre.przywara@arm.com

.../selftests/cachestat/test_cachestat.c | 22 ++++++++++++++++++- 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/cachestat/test_cachestat.c b/tools/testing/selftests/cachestat/test_cachestat.c index a5a4ac8dcb76c..77620e7ecf562 100644 --- a/tools/testing/selftests/cachestat/test_cachestat.c +++ b/tools/testing/selftests/cachestat/test_cachestat.c @@ -15,6 +15,8 @@ #include "../kselftest.h" +#define NR_TESTS 8

• static const char * const dev_files[] = { "/dev/zero", "/dev/null", "/dev/urandom", "/proc/version", "/proc"

@@ -235,7 +237,25 @@ bool test_cachestat_shmem(void) int main(void) {

• int ret = 0;

• int ret;
• ksft_print_header();
• ret = syscall(__NR_cachestat, -1, NULL, NULL, 0);
• if (ret == -1 && errno == ENOSYS) {

• printf("1..0 # Skipped: cachestat syscall not available\n");
  

• return KSFT_SKIP;  
  

What happens when other errors besides ENOSYS? The test shouldn't continue.

-1 is an illegal file descriptor, and this is checked below (still using the same ret and errno), but reported using the normal framework. This check above is done early, before we even announce the plan, so that we can skip *all* of the tests, since they don't make any sense when the syscall is not available at all.

Does that make sense?

Cheers, Andre

...

• }
• ksft_set_plan(NR_TESTS);
• if (ret == -1 && errno == EBADF) {

• ksft_test_result_pass("bad file descriptor recognized\n");
  

• ret = 0;
  

• } else {

• ksft_test_result_fail("bad file descriptor ignored\n");
  

• ret = 1;
  

• }

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

thanks, -- Shuah