[PATCH] tests: chdir.test

[Jay Joshi]

Thanks.
One more query: I'm not able to see any usage of "link" syscall in
tests subdir. Although, covecov is highlighting "link" syscall in
green, which I presume indicates test for that syscall is covered.
What am I missing here?

On Sat, Mar 12, 2016 at 9:20 PM, Dmitry V. Levin <ldv at altlinux.org> wrote:
> On Sat, Mar 12, 2016 at 01:37:20PM +0530, Jay Joshi wrote:
>> On Sat, Mar 12, 2016 at 7:53 AM, Dmitry V. Levin wrote:
>> > On Fri, Mar 11, 2016 at 11:22:23PM +0530, Jay Joshi wrote:
>> > >
>> > > This is my first attempt to add test for syscall (here, chdir). Any
>> > > suggestion, comment, criticism is welcomed.
>> >
>> > chdir is already well covered, see
>> > $ git grep chdir tests
>> >
>> > You must have missed my recommendation to check current coverage report
>> > at https://codecov.io/github/strace/strace before adding new tests.
>> >
>> > I think you'd rather take something that's not tested at all.
>>
>> Thanks. I couldn't understand coverage structure properly. Is coverage
>> calculated manually, semi-automatically or automatically?
>
> It's fully automatic, see travis-ci.sh script.
>
>> > > +#if defined __NR_chdir
>> >
>> > Why do you think that libc wrapper for chdir syscall is not suitable?
>>
>> Syscall should only be used when glibc wrapper function for that
>> syscall is not available. Please correct me if I'm wrong.
>
> Either not available or implemented using different system call(s).
>
>> If so, what
>> is the advantage of using syscall function for, say "chmod"? Please
>> help me understand where to use what.
>
> Some recently added architectures (see e.g. linux/32/syscallent.h and
> linux/64/syscallent.h) provide no "chmod" syscall; on these architectures,
> "chmod" libc wrapper uses "fchmodat" syscall.
>
> This is certainly not the case for "chdir"; there seems to be no other way
> to implement "chdir" besides calling "chdir" syscall.
>
>> > > +  if (errno == ENOSYS) {
>> > > +    printf("chdir(\"%s\") = -1 ENOSYS (%m)\n", sample_dir);
>> >
>> > chdir failing with ENOSYS?  Really?
>>
>> Not sure. Where can I find whether system would have surely
>> implemented a particular system call? In other words, would never
>> throw ENOSYS.
>
> Besides syscalls marked with NF flag
> (see git grep -Fw NF linux/*/syscallent*.h), there is no single place that
> would give you an answer for this question, which is just a special case
> for a more general question how a particular system call works on
> different architectures and kernel versions.
>
> manual page usually answers the question whether the function implemented
> by syscall is mandatory and when the system call was introduced in the
> kernel.
>
> linux/*/syscallent*.h answers the question whether the syscall is hooked
> up in all architectures.
>
> General understanding of linux kernel helps to find out alternative
> syscalls or prove their absense.
>
>
> --
> ldv
>
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