[LTP] [PATCH v2 1/2] syscalls/pidfd_open01.c: Add check for close-on-exec flag

[Xiao Yang <yangx.jy@cn.fujitsu.com>]

On 2020/5/13 17:20, Petr Vorel wrote:
> Hi Yang,
>
>> For the patch set, I and Viresh have the following doubts so do you have any
>> suggestion about them?
>> 1) I keep TEST() in pidfd_open01/pidfd_open03 for now but I think it is
>>     surplus because pidfd/fd and TERRNO are enough to check return value
>>     and errno.
>>     I wonder if it is necessary to keep TEST()?
>
> yes, I've noticed your discussion at v1, sorry I wasn't able to follow.
> https://patchwork.ozlabs.org/project/ltp/patch/20200430085742.1663-1-yangx.jy@cn.fujitsu.com/
> Just to get context, We're talking about part of the changes between v1 and v2:
>
> +++ b/testcases/kernel/syscalls/pidfd_open/pidfd_open03.c
> @@ -27,9 +27,11 @@ static void run(void)
>                  exit(EXIT_SUCCESS);
>          }
>
> -       fd = pidfd_open(pid, 0);
> +       TEST(pidfd_open(pid, 0));
> +
> +       fd = TST_RET;
>          if (fd == -1)
> -               tst_brk(TFAIL | TERRNO, "pidfd_open() failed");
> +               tst_brk(TFAIL | TTERRNO, "pidfd_open() failed");
>
>          TST_CHECKPOINT_WAKE(0);
>
> I haven't found Cyril's request to use TEST(). To be honest, not sure if it was
> meant to make sure that errno needs to be reset before (which TEST()) does.
> If not, using pidfd_open() directly would be ok for me.
Hi Petr,

Thanks a lot for your quick reply.

Resetting errno may not necessary because errno will be set again when
fd == -1.

>
>
>> 2) tst_syscall() is enough to check the support of pidfd_open() and I
>>     don't want to define check function as fsopen_supported_by_kernel()
>>     does.
>>     Do you think so?
>
>> BTW:
>> I don't like the implementation of fsopen_supported_by_kernel():
>> a) syscall()/tst_syscall() is enough to check the support of
>> pidfd_open(2) and 'tst_kvercmp(5, 2, 0))<  0' will skip the check if
> +1 for tst_syscall()
>
>> a kernel on distribution is newer than v5.2 but drop the support of
>> pidfd_open(2) on purpose.
> "drop support of pidfd_open(2) on purpose": would anybody has a reason to do
> that?

As my pervious mail said, It is just a possible situation? for example:
Upstream kernel introduces btrfs filesystem long long ago but the
kernel of RHEL8 drops btrfs filesystem because of some reasons.

It is just a reason used to explain why I want to drop the kernel 
version check.

>
>> b) tst_syscall() has checked ENOSYS error so we can simple
>> fsopen_supported_by_kernel() by replacing syscall() with tst_syscalls().
>
> Well, one of the benefits of fsopen_supported_by_kernel() was to reduce a bit of
> duplicity. Even if the implementation is like TEST and SAFE_CLOSE(), it's
> a fewer lines (+ function name as a self docs).
>
> void fsopen_supported_by_kernel(void)
> {
> 	TEST(tst_syscall(__NR_fsopen, NULL, 0));
> 	if (TST_RET != -1)
> 		SAFE_CLOSE(TST_RET);
> }
>
> For your change for pidfd_open03.c:
>
> static void setup(void)
> {
> 	int pidfd = -1;
>
> 	// Check if pidfd_open(2) is not supported
> 	pidfd = tst_syscall(__NR_pidfd_open, getpid(), 0);
> 	if (pidfd != -1)
> 		SAFE_CLOSE(pidfd);
> }
>
>   static struct tst_test test = {
> -       .min_kver = "5.3",
> +       .setup = setup,
>
> How about to call the function pidfd_open_supported_by_kernel()?

OK

> Than you can remove the comment (which BTW should use C style /* */).

OK

> And IMHO you don't have to assign pidfd to -1.

In pidfd_open_supported_by_kernel(), do you want to drop 'pidfd = -1' 
directly or drop 'pidfd = -1' by using TEST()?

Best Regards,
Xiao Yang
>
> Kind regards,
> Petr
>
>
> .
>