[LTP] [PATCH v4] syscalls/prctl02: add more error tests

[Yang Xu]

on 2019/11/12 18:10, Cyril Hrubis wrote:

> Hi!
>>> 1) Add fallback definitions to lapi
>>> 2) Ensure these tests does not fail on older kernels
>>>
>>>      We do expect EINVAL in these cases anyways, which is what we would
>>>      get if the prctl() option is unknown to the kernel anyways, so here
>>>      we can just get rid of these ifdefs and things should work fine.
>> For me, a fallback definitions into the lapi header is only for fixing undefined error on old kernel.
>>
>> IMO, we only test options that kernel supports.
>> If we test an unsupported option, our case reports EINVAL that will give user a false impression(kernel
>> supports it, but argument or environment is bad). I think we should check they whether supported before run
>> (ifdef is a way).
> However using ifdefs to assert kernel features never worked at all. The
> kernel headers usally lag behind the installed kernel in distribution
> and it's even more wrong when you are testing latest kernel on any given
> distro.
>
> If you want to check for kernel support the best thing is to use the
> tst_kvercmp() that checks the kernel version and even that does not work
> 100% reliably.

Yes. most distros backport upstream kernel patch and tst_kvercmp maybe useless.

>> ps: If we test EPERM error(cap is not in PI or PP) of PR_CAP_AMBIENT on old kernel,  they will report EINVAL.
>> So, I think ifdef is needed.
> No, ifdefs are never solution here. It will still fail if you compiled
> the test on newer distro and booted it up with older kernel.

Now, I agree with you. If new distro and booted it with older kernel, the ifdef is useless. I think we should use correct argument
as xiao said to check whether kernel supports these options.

>


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